Naked Science Forum

Non Life Sciences => Technology => Topic started by: teragram on 23/09/2019 22:59:43

Title: Is this a stunning breakthrough in petrol engine thermal efficiency?
Post by: teragram on 23/09/2019 22:59:43
I refer to a magazine advert for the BMW 3 Series Plug-in Hybrid, in particular the quoted fuel consumption figures:-
Mpg(ltr/100Km) (weighted combined): 176.6 (1.6) to 201.8 (1.4). CO2 emissions (weighted) 36gm/Km.
Electric energy consumption (weighted combined) 15.4 - 14.8 KWh/100Km.
To make it easy I assume that 1ltr of petrol contains 10 KWh of energy

I don't know how these figures are arrived at, but on the face of it, 1.6 ltr/100Km = 16 KWh/100Km. If the "Electrical energy consumption" is 15.4 KWh/100Km, does this mean that the overall thermal efficiency is 15.4/16 = 96%?
What am I missing?
Title: Re: Is this a stunning breakthrough in petrol engine thermal efficiency?
Post by: Petrochemicals on 23/09/2019 23:51:48
I refer to a magazine advert for the BMW 3 Series Plug-in Hybrid, in particular the quoted fuel consumption figures:-
Mpg(ltr/100Km) (weighted combined): 176.6 (1.6) to 201.8 (1.4). CO2 emissions (weighted) 36gm/Km.
Electric energy consumption (weighted combined) 15.4 - 14.8 KWh/100Km.
To make it easy I assume that 1ltr of petrol contains 10 KWh of energy

I don't know how these figures are arrived at, but on the face of it, 1.6 ltr/100Km = 16 KWh/100Km. If the "Electrical energy consumption" is 15.4 KWh/100Km, does this mean that the overall thermal efficiency is 15.4/16 = 96%?
What am I missing?

My reading is 176 litres ler 100 km or 2 gallon per mile, this is more than the 10mpg of the pegani zonda, perhaps its charging the battery at the same time ?
Title: Re: Is this a stunning breakthrough in petrol engine thermal efficiency?
Post by: alancalverd on 24/09/2019 00:50:36
If you start with a full 12.5 kWh battery (standard fit for a BMW3) and 1 liter of gas, you would expect to cover about 2.5 times the distance on battery power alone (over 90% efficient) as on the gasoline, say 40 miles total. At 4.5 liter/gallon you could argue (incorrectly, but we are talking "advertising maths", not the real stuff) that this is equivalent to almost 180 mpg. 

Actual road test figures yield around 65 mpg with a brand new battery, because if you started with a full battery and one liter of gas you would only cover 40 miles before the machine stopped. You would then have to recharge the battery with engine power, which is way less than 50% efficient at converting gasoline to electricity and is just a waste of time - you might as well use the engine to drive the wheels directly.

Looking at actual figures for hybrid taxis (I use a lot of taxis) they get around 60 mpg because they recharge the battery from the mains whenever possible and generally only do short runs. Gasoline mileage on a long run without mains recharging rarely exceeds 50 mpg for a Prius, no better than a 2 liter diesel. The energetic value of a "self-charging hybrid" is in regenerative braking and short-term acceleration, hence the attraction for taxis and city driving. In a sustained cruise you are just lugging the extra weight of a dead battery. 

Fact is that you can't get something for nothing, but the tax on electricity is a lot lower than on gasoline.
Title: Re: Is this a stunning breakthrough in petrol engine thermal efficiency?
Post by: teragram on 26/09/2019 23:03:51
Looking at actual figures for hybrid taxis (I use a lot of taxis) they get around 60 mpg because they recharge the battery from the mains whenever possible and generally only do short runs. Gasoline mileage on a long run without mains recharging rarely exceeds 50 mpg for a Prius, no better than a 2 liter diesel.

My apologies, I omitted the stated battery range which is 34 - 37miles.
As you say, people charge mostly from mains electricity. If you always were able to do that, you could claim the petrol consumption per 100Km to be zero.
Smoke and mirrors trickery?
Sad in my opinion that this sort of misrepresentation is allowed in advertising.

Title: Re: Is this a stunning breakthrough in petrol engine thermal efficiency, but it
Post by: alancalverd on 27/09/2019 10:22:19
...and politics.

"Free" electricity comes at a huge cost of fossil fuel required to build, maintain and dismantle the windmills and maintain uneconomic standby plant for when the wind isn't blowing, but it's paid for by those of us who used the fuel more directly. The overall efficiency of the best thermal* power stations is no better than a small diesel engine, but the tax on their fuel is lower. Likewise the energy payback on solar panels is questionable by the time you have added a reasonable amount of storage and accounted for the limited life of batteries, but it doesn't matter in politics because all the toxic waste and coal-fired power that goes into making the kit, only poisons Chinese workers, and makes a huge profit for Chinese capitalists (who don't exist under communism, of course, but somebody somewhere is pocketing the cash and shaking hands with British ministers).

The electric car is just another bonus for the rich, subsidised by the poor. Can't wait to get mine, but it will be a hybrid with a very small battery for acceleration and braking only, powered by a gas turbine or cooking oil diesel.

*I note that the cost of Britain's next nuclear power station has just increased again. Somebody has discovered that Somerset is boggy - a fact only known to bronze-age farmers and Roman soldiers, apparently. 
Title: Re: Is this a stunning breakthrough in petrol engine thermal efficiency?
Post by: teragram on 30/09/2019 16:22:47
...and politics. "Free" electricity comes at a huge cost of fossil fuel required to build, maintain and dismantle the windmills and maintain uneconomic standby plant for when the wind isn't blowing, but it's paid for by those of us who used the fuel more directly. The overall efficiency of the best thermal* power stations is no better than a small diesel engine, but the tax on their fuel is lower. Likewise the energy payback on solar panels is questionable by the time you have added a reasonable amount of storage and accounted for the limited life of batteries, but it doesn't matter in politics because all the toxic waste and coal-fired power that goes into making the kit, only poisons Chinese workers, and makes a huge profit for Chinese capitalists (who don't exist under communism, of course, but somebody somewhere is pocketing the cash and shaking hands with British ministers).The electric car is just another bonus for the rich, subsidised by the poor. Can't wait to get mine, but it will be a hybrid with a very small battery for acceleration and braking only, powered by a gas turbine or cooking oil diesel. *I note that the cost of Britain's next nuclear power station has just increased again. Somebody has discovered that Somerset is boggy - a fact only known to bronze-age farmers and Roman soldiers, apparently. 


""Free" electricity comes at a huge cost of fossil fuel required to build, maintain and dismantle the windmills and maintain uneconomic standby plant for when the wind isn't blowing, but it's paid for by those of us who used the fuel more directly."

I think we're going a bit off theme here. I don't think I implied that electricity for hybrid cars is free, merely that it's cost is not included in the consumption stats., resulting in impossible claims being allowed in advertisements.
As regards who pays for renewable  infra-structure:-

Quote from Vox.com May 2019:-
"The International Monetary Fund periodically assesses global subsidies for fossil fuels as part of its work on climate, and it found in a recent working paper that the fossil fuel industry got a whopping $5.2 trillion in subsidies in 2017. This amounts to 6.4 percent of the global gross domestic product."

From <https://www.vox.com/2019/5/17/18624740/fossil-fuel-subsidies-climate-imf>

Report in The Guardian, Jan 2019:-
"The UK leads the European Union in giving subsidies to fossil fuels, according to a report from the European commission. It found €12bn (£10.5bn) a year in support for fossil fuels in the UK, significantly more than the €8.3bn spent on renewable energy.
The commission report warned that the total subsidies for coal, oil and gas across the EU remained at the same level as 2008. This is despite both the EU and G20 having long pledged to phase out the subsidies, which hamper the rapid transition to clean energy needed to fight climate change."

House of Commons Library:_
"Taxing aviation fuel Standard Note: SN00523 Last updated: 2 October 2012 Author: Antony Seely Section Business & Transport Section 
At present, although road fuel is charged excise duty, which represents a substantial proportion of the pump price paid by motorists, aviation kerosene (AVTUR) which is used in jet engines is exempt from this tax.
Many commentators have argued that this is an indefensible anomaly, given that aviation accounts for a growing share of greenhouse gas emissions.  However, there are several obstacles to taxing aviation fuel.  First, it is probable that unilateral moves by the UK to impose duty on this category of fuel would be counterproductive, and contrary to EU law."

So another "advantage" then for the UK is that it will be able to add tax to jet fuel when we complete the process of our (self-destruction) exit from the EU. 

What is the efficiency of a small gas turbine? I seem to remember that development of the 1970's Rover gas turbine car was stopped partly because of heavy fuel consumption. Also, would the amount of waste cooking oil produced be sufficient to run all the diesel vehicles currently on the roads?
True that we have exported much of our pollution to China, largely because UK governments have continued Mrs Thatcher's policy of winding down industry in general.

Title: Re: Is this a stunning breakthrough in petrol engine thermal efficiency?
Post by: alancalverd on 30/09/2019 18:39:16
AVTUR is tax-exempt everywhere by agreement of the ICAO. The EU is not the principal consumer of aviation fuel. There is a reasonable presumption that any flight from A to B will prompt a return flight from B to A. It is always desirable to arrive with minimum fuel (plus your mandatory reserve). If fuel was noticeably cheaper at B, you would overfill for the return flight to save money. But extra fuel on the ground = extra fuel consumption  en route (to lug all that fuel off the deck)  and reduces your payload capacity, so by common sense, everyone agrees to minimise the cost differential between countries.

Interestingly, although AVGAS is horrendously taxed in the UK, I can reclaim the VAT on any that I export. So it's worth filling the tank of the old Cessna (5 hours endurance) for a flight to France (1 hour each way) or Ireland. Great fun doing the paperwork for an occasional trip, but imagine the aggravation if airlines insisted on routing London-Dublin-Belfast ten times a day to save money instead of flying direct. 

If the UK taxes AVTUR, the airports will go broke. Everyone will fly to Paris or Amsterdam as a hub, use small planes to link to the UK and not buy fuel here.

Gas turbines are very efficient at constant speed, which is why they are used for ships and aircraft, and for generating electricity. The Rover gas turbine racing car needed a huge mechanical reduction gear ratio to the road wheels with a resulting heavy, inefficient gearbox. It was amazingly quiet and accelerated well, but only managed about 8 mpg due to the variable speed demand of road transport and the extra weight of the gear system and ancillary plumbing needed for a variable speed turbine.

If you can buffer a turbine-generator system with a battery, you can use modern electronic control instead of a gearbox to drive the traction motors. This is likely to power the next generation of training and general purpose aircraft where you are doing a lot of short trips, for which piston engines are currently more fuel-efficient than jets. The intermediate solution is actually aviation diesel engines running on tax-free AVTUR and driving propellors.

Road transport (and transport in general) is so important for the health and welfare of all, that taxing fuel has negligible impact on consumption - it just increases the cost of everything.
Title: Re: Is this a stunning breakthrough in petrol engine thermal efficiency?
Post by: Bored chemist on 30/09/2019 20:13:57
by common sense, everyone agrees to minimise the cost differential between countries.
It's true that the differential is driven to near zero.
But if every country in the world  taxed it at the same rate their governments would make lots of money.
This would, of course, make flying more expensive.
In turn, that would reduce demand and thus reduce the consumption of aviation fuel together with the associated production of CO2.
Title: Re: Is this a stunning breakthrough in petrol engine thermal efficiency?
Post by: teragram on 30/09/2019 23:40:55
If you can
AVTUR is tax-exempt everywhere by agreement of the ICAO. The EU is not the principal consumer of aviation fuel. There is a reasonable presumption that any flight from A to B will prompt a return flight from B to A. It is always desirable to arrive with minimum fuel (plus your mandatory reserve). If fuel was noticeably cheaper at B, you would overfill for the return flight to save money. But extra fuel on the ground = extra fuel consumption  en route (to lug all that fuel off the deck)  and reduces your payload capacity, so by common sense, everyone agrees to minimise the cost differential between countries.

Interestingly, although AVGAS is horrendously taxed in the UK, I can reclaim the VAT on any that I export. So it's worth filling the tank of the old Cessna (5 hours endurance) for a flight to France (1 hour each way) or Ireland. Great fun doing the paperwork for an occasional trip, but imagine the aggravation if airlines insisted on routing London-Dublin-Belfast ten times a day to save money instead of flying direct. 

If the UK taxes AVTUR, the airports will go broke. Everyone will fly to Paris or Amsterdam as a hub, use small planes to link to the UK and not buy fuel here.

Gas turbines are very efficient at constant speed, which is why they are used for ships and aircraft, and for generating electricity. The Rover gas turbine racing car needed a huge mechanical reduction gear ratio to the road wheels with a resulting heavy, inefficient gearbox. It was amazingly quiet and accelerated well, but only managed about 8 mpg due to the variable speed demand of road transport and the extra weight of the gear system and ancillary plumbing needed for a variable speed turbine.

If you can buffer a turbine-generator system with a battery, you can use modern electronic control instead of a gearbox to drive the traction motors. This is likely to power the next generation of training and general purpose aircraft where you are doing a lot of short trips, for which piston engines are currently more fuel-efficient than jets. The intermediate solution is actually aviation diesel engines running on tax-free AVTUR and driving propellors.

Road transport (and transport in general) is so important for the health and welfare of all, that taxing fuel has negligible impact on consumption - it just increases the cost of everything.


Most informative, but all this tax exemption represents a large subsidy for fossil fuel, whether locally or international, which was my point.
For the record, it seems that Rover started development of a gas turbine car at the end of World War 2, having been involved during the war in research on Frank Whittles ideas. I was not though referring to the Rover BRM racing car. Whatever machine is used, if it runs by burning stuff it is very difficult to wean it off fossil fuel.
Title: Re: Is this a stunning breakthrough in petrol engine thermal efficiency?
Post by: teragram on 30/09/2019 23:47:27
This would, of course, make flying more expensive.In turn, that would reduce demand and thus reduce the consumption of aviation fuel together with the associated production of CO2.


Which would be a huge environmental advantage.


Title: Re: Is this a stunning breakthrough in petrol engine thermal efficiency?
Post by: alancalverd on 01/10/2019 00:04:55
If you make flying more expensive, you increase the cost of air freight, which destroys the economy of emerging agricultural nations like Kenya and Peru and hurts the poorest in the consuming nations (like the UK).

It's somewhat bizarre logic to equate not taxing something as subsidising it. The reason electricity is affordable is because there is no tax on the fossil fuel that makes it, but there is a levy to subsidise unreliable sources. And VAT on domestic electricity, because the European Union has decided that, like tampons, it is an unnecessary luxury.

The reason Rolls Royce make jet engines is because Rover, who were granted the original licence to Whittle's patent, made a complete pig's ear of the project.
Title: Re: Is this a stunning breakthrough in petrol engine thermal efficiency?
Post by: teragram on 02/10/2019 22:26:00
If you make flying more expensive, you increase the cost of air freight, which destroys the economy of emerging agricultural nations like Kenya and Peru and hurts the poorest in the consuming nations (like the UK). It's somewhat bizarre logic to equate not taxing something as subsidising it. The reason electricity is affordable is because there is no tax on the fossil fuel that makes it, but there is a levy to subsidise unreliable sources. And VAT on domestic electricity, because the European Union has decided that, like tampons, it is an unnecessary luxury.

Air fuel tax exemption must of course be ended in all countries. You could make aircraft fuel for freight tax exempt, thus protecting the economy of emerging nations, whilst removing tax exemption for passenger flights, again, internationally. This may spur more enthusiastic attempts to reduce aircraft CO2 production.
The logic that equates tax exemption with subsidy is surely that:-
Subsidies come from government funds, largely collected by taxation. Tax exemption is a subsidy by virtue of the fact that the tax money that would provide the "virtual" subsidy is not collected in the first place.

"...but there is a levy to subsidise unreliable sources."
 And very expensive ones. I remember during the last Cameron government that an "extra £1 billion was to be given to North Sea production projects for that year.

My apologies to (un)interested observers:-
The original theme has branched even further because I attempted in Reply #5 to clarify the commonly held belief that sustainable energy is the sole sink for taxpayer support for energy infrastructure.
Title: Re: Is this a stunning breakthrough in petrol engine thermal efficiency?
Post by: alancalverd on 03/10/2019 08:17:37
So I must thank the government for subsidising air. I smell communism!

Aviation fuel tax is a small minefield. A significant amount of occasional high-value freight is carried on passenger flights. Around the UK, island scheduled and air taxi services carry mail, food, tourists, patients, human and veterinary pharmaceuticals, business travellers and officials. Are you suggesting that tax should be charged on each flight according to the load manifest?  Or would you rather be transferred to a mainland hospital by sailboat?



Title: Re: Is this a stunning breakthrough in petrol engine thermal efficiency?
Post by: syhprum on 03/10/2019 12:57:13
Why is private medical treatment not subject to VAT ? if I send my car for service to have its life extended I am charged VAT but if I send my body to a private hospital have its life extended I am costing the pension funds money but pay no VAT. 
Title: Re: Is this a stunning breakthrough in petrol engine thermal efficiency?
Post by: alancalverd on 03/10/2019 13:57:53
Because not all public health services are free of charge. If you start charging VAT on private prescriptions or cosmetic fillings you end up employing accountants and lawyers instead of pharmacists and dentists. Far simpler just to decide that some sectors are VAT-free.

I'm actually in favour of VAT. It's a small admin burden on my business but improves cash flow and, unlike all the other taxes I pay, it's unavoidable as it is based on actual turnover, not declared profit, and collected at the point of final transaction, not where the business is registered. If we abolished all other taxes and charged 40% VAT on every transaction, we could get rid of a whole raft of tax inspectors, accountants and lawyers, and encourage enterprise (no capital gains tax on investment, no corporation tax on profit, no need for PAYE and NI deductions for employees….)
Title: Re: Is this a stunning breakthrough in petrol engine thermal efficiency?
Post by: teragram on 03/10/2019 21:22:44
Aviation fuel tax is a small minefield. A significant amount of occasional high-value freight is carried on passenger flights. Around the UK, island scheduled and air taxi services carry mail, food, tourists, patients, human and veterinary pharmaceuticals, business travellers and officials. Are you suggesting that tax should be charged on each flight according to the load manifest?  Or would you rather be transferred to a mainland hospital by sailboat?

So a partial solution would be to raise tax on air passenger tickets only. A substantial reduction in pollution could perhaps be achieved by encouraging fewer people to fly to other countries for stag and hen parties, weddings, visiting Disneyworld, major sporting events etc. After all it is very necessary to address the problem of aircraft emissions.


Title: Re: Is this a stunning breakthrough in petrol engine thermal efficiency?
Post by: alancalverd on 04/10/2019 00:16:40
There is already an air passenger tax on flights from the UK. The remarkable fact is that if you deduct the tax, airlines can still make a profit on their lowest fares. This is due to the fuel efficiency of air transport. The actual operating cost from London to Edinburgh, once you have deducted tax and landing and handling fees, is about £10 per passenger - the price of 8 gallons of fuel, but including maintenance, depreciation, and crew wages. You might drive that distance on 8 gallons of diesel, but the Treasury mileage rate (which allows for depreciation and maintenance) works out at about £160, so even with four people in the car, the plane is more fuel-efficient, safer, and 10 times quicker. Plus, of course, it doesn't need a road and disperses its effluent high above the clouds, with negligible particulates.

Elsewhere in this forum I compared the carbon footprint of building and operating the HS2 railway (no actual track laid yet, after 6 years and some £20,000,000,000 of your money) with shifting the same number of passengers by air (start tomorrow for £20,000,000). No prizes for guessing which was cheaper and better for the environment.
Title: Re: Is this a stunning breakthrough in petrol engine thermal efficiency?
Post by: teragram on 05/10/2019 21:10:38
There is already an air passenger tax on flights from the UK. The remarkable fact is that if you deduct the tax, airlines can still make a profit on their lowest fares. This is due to the fuel efficiency of air transport. The actual operating cost from London to Edinburgh, once you have deducted tax and landing and handling fees, is about £10 per passenger - the price of 8 gallons of fuel, but including maintenance, depreciation, and crew wages. You might drive that distance on 8 gallons of diesel, but the Treasury mileage rate (which allows for depreciation and maintenance) works out at about £160, so even with four people in the car, the plane is more fuel-efficient, safer, and 10 times quicker. Plus, of course, it doesn't need a road and disperses its effluent high above the clouds, with negligible particulates.

Fuel efficiency doesn't necessarily equate with Treasury mileage rate? So should we say that the aircraft is more tax-efficient, not more fuel efficient? And is the 8 gallons of fuel for £10 a special rate for air passenger travel? I currently pay over £40 for that much fuel.
Does it only cost £10 to transport a passenger 325 miles? The cheapest fare I found (not used to this) was £44

The fact is that air travel is so cheap that millions of people are able to fly frequently anywhere in the world  in large numbers, and for often frivolous reasons, across distances that would rarely be considered if land travel only was available.
I understand that aircraft consume fuel at the rate (depending on type) of 2.5 to 12 tonnes per hour. As regards specifying consumption in passenger miles per gallon, the point is that the environment doesn't care how many people have produced all that pollution, only that it has been produced.

"...disperses it's effluent high above the clouds..."
Where it has an effect apparently 2 to 4 times as bad as those dispersed at ground level.

Title: Re: Is this a stunning breakthrough in petrol engine thermal efficiency?
Post by: alancalverd on 06/10/2019 15:58:08
Does it only cost £10 to transport a passenger 325 miles? The cheapest fare I found (not used to this) was £44
Yes. The airline has to pay passenger tax, navigation charges, and airport handling charges, and make a profit. As I stated, £10 is the actual cost of fuel, crew wages and aircraft maintenance and depreciation.

Quote
The fact is that air travel is so cheap that millions of people are able to fly frequently anywhere in the world  in large numbers, and for often frivolous reasons, across distances that would rarely be considered if land travel only was available.
You are required to state "purpose of travel" on immigration documents. Are you suggesting that there should be an extra tax for frivolous travel? Would anyone admit to it?  I'd happily charge £10 per mile for any passenger who spoke above 50 decibels or claimed to be a nervous/confident/frequent/novice flyer.
Quote
I understand that aircraft consume fuel at the rate (depending on type) of 2.5 to 12 tonnes per hour.
Unlikely. Mine only weighs a ton fully loaded, and will fly for about 6 hours (700 miles)  on a full tank (0.1 ton).
Quote
As regards specifying consumption in passenger miles per gallon, the point is that the environment doesn't care how many people have produced all that pollution, only that it has been produced.
All living things pollute their environment. It's a question of choice.
Title: Re: Is this a stunning breakthrough in petrol engine thermal efficiency?
Post by: teragram on 07/10/2019 22:12:25
Unlikely. Mine only weighs a ton fully loaded, and will fly for about 6 hours (700 miles)  on a full tank (0.1 ton).

So 700 miles on 100 Kg = 7 miles per Kg? So scale up to a 100 tonne aircraft and passengers and that might become 0.07 mile per Kg, and at 500 mph in one hour would be 7100Kg?

It seems that a Boeing 747 (which model I don't know) consumes about one gallon of fuel per second at cruising altitude. I assume US gallons, so 3.8litrs * 3600 seconds = 13680 litres per hour, or if fuel density is 0.8Kg per litre, 0.8 * 13680 = 10944Kgs or almost eleven tonnes. I know that more modern aircraft are more efficient, but I think the 747 is still the most common amongst large aircraft.

Title: Re: Is this a stunning breakthrough in petrol engine thermal efficiency?
Post by: teragram on 07/10/2019 22:14:48
You are required to state "purpose of travel" on immigration documents. Are you suggesting that there should be an extra tax for frivolous travel? Would anyone admit to it?  I'd happily charge £10 per mile for any passenger who spoke above 50 decibels or claimed to be a nervous/confident/frequent/novice flyer.

I think you know that by "frivolous" I mean in this context, as I have said, travelling great distances for stag and hen parties, weddings, sporting events, entertainment events, tourist attractions such as Disney World, etc. How many people travel to Olympic Games, football, rugby, cricket, athletics events, and what is the cost in tonnes of CO2? And couldn't they watch them on TV?
Title: Re: Is this a stunning breakthrough in petrol engine thermal efficiency?
Post by: teragram on 07/10/2019 22:23:27
All living things pollute their environment. It's a question of choice.

But other species have not reached sufficient numbers to overwhelm the environment.
And we have the choice, to try and reduce our impact and leave conditions in not to bad a state for those that come after us.
Title: Re: Is this a stunning breakthrough in petrol engine thermal efficiency?
Post by: alancalverd on 08/10/2019 06:59:55
So 700 miles on 100 Kg = 7 miles per Kg? So scale up to a 100 tonne aircraft and passengers and that might become 0.07 mile per Kg, and at 500 mph in one hour would be 7100Kg?
Shifting stuff consumes fuel. A 747 drinks about 8 gallons/mile when carrying 400 passengers and their baggage, i.e 50 passenger-miles per gallon. That's about the average for petrol cars, which rarely carry more than two occupants, whereas airliners are usually 80 -  90% loaded.

Modern airliners are more efficient- remember the 747 is 50 years old! - although interestingly the Airbus 380 isn't: its attraction is in the reduced administrative overheads of shifting more passengers (up to 850) in a single airway and ground handling slot.
Title: Re: Is this a stunning breakthrough in petrol engine thermal efficiency?
Post by: teragram on 20/10/2019 15:14:57
Shifting stuff consumes fuel. A 747 drinks about 8 gallons/mile when carrying 400 passengers and their baggage, i.e 50 passenger-miles per gallon. That's about the average for petrol cars, which rarely carry more than two occupants, whereas airliners are usually 80 -  90% loaded. Modern airliners are more efficient- remember the 747 is 50 years old! - although interestingly the Airbus 380 isn't: its attraction is in the reduced administrative overheads of shifting more passengers (up to 850) in a single airway and ground handling slot.

So we should only move stuff by air if that stuff NEEDS to be moved, ie to disaster areas, war zones, medical supplies etc.
But my point is that stating fuel consumption in terms of passenger miles per gal/litr only shifts focus from the large amounts of fuel used per flight. It is I think an accountancy measure rather than a scientific measure. And the equivalent amount of fuel would never be used for travel if air travel weren't so cheaply available. The numbers of  people travelling thousands of miles in cars would never remotely approach the numbers of airline passengers.

Title: Re: Is this a stunning breakthrough in petrol engine thermal efficiency?
Post by: alancalverd on 20/10/2019 17:03:39
But my point is that stating fuel consumption in terms of passenger miles per gal/litr only shifts focus from the large amounts of fuel used per flight. It is I think an accountancy measure rather than a scientific measure

Rubbish! The whole point of transport is to move people or stuff from A to B, and you measure the efficiency of any modality by the quantity of fuel needed to shift one unit of payload (passenger or ton of freight) one mile. The fuel required to move an empty train or ship is enormous and the efficiency thereof is zero.

Nothing NEEDS to be moved, and commuting to an office is surely the greatest waste of time and fuel ever invented. We move stuff (including ourselves) because we want it somewhere else - though I don't know of anyone who would rather be in an office than at home.
Title: Re: Is this a stunning breakthrough in petrol engine thermal efficiency?
Post by: teragram on 24/10/2019 21:17:14
Rubbish! The whole point of transport is to move people or stuff from A to B, and you measure the efficiency of any modality by the quantity of fuel needed to shift one unit of payload (passenger or ton of freight) one mile. The fuel required to move an empty train or ship is enormous and the efficiency thereof is zero. Nothing NEEDS to be moved, and commuting to an office is surely the greatest waste of time and fuel ever invented. We move stuff (including ourselves) because we want it somewhere else - though I don't know of anyone who would rather be in an office than at home.

So if nothing NEEDS to be moved,...…...
This is my point, who really NEEDS to fly many hundreds of miles on stag or hen parties, weddings, international sports events, music festivals or even holidays? All these passenger miles are unnecessarily contributing hugely to atmospheric pollution. And instead of discouraging people from flying we reward them by giving even cheaper flights under air miles schemes. The aim should be to drastically reduce the number of long distance journeys, and given that there are thought to be on average of 93,000 airline flights daily around the world, a good starting point would be the air travel industries.
Unloaded vehicles have 0% efficiency, so what would (the theoretical) 100% be in terms of passengers or tonnes of freight?  Bearing in mind that what we need is very substantial reductions in the fuel used per flight, regardless of per passenger.

Let's not forget that glaciers are shrinking, and polar ice is melting at rates that were not previously predicted by meteorological scientists.


Title: Re: Is this a stunning breakthrough in petrol engine thermal efficiency?
Post by: alancalverd on 24/10/2019 23:44:19
 
Bearing in mind that what we need is very substantial reductions in the fuel used per flight, regardless of per passenger.
Utter drivel. Airliners do not fly for the fun of it, but to make a profit. This depends on filling the seats, because there is no other source of income. So the selling point of an airplane is the number of passenger miles you can get for a gallon of fuel, because fuel is a cost.

I didn't state efficiency as a percentage and you are  misleading yourself by doing so. Transport efficiency is a dimensional quantity, passenger or freight ton miles per gallon. That is a scientific measure of what you get out divided by what you put in, which is the definition of efficiency. If you want to consider thermal efficiency (a dimensionless ratio, and thus expressible as a percentage), jet engines approach 60%, way above the thermal efficiency of any form of surface transport apart from large marine diesels. You could save a bit of fuel by using sea transport, but as an example London-Cape Town takes 30 days by sea or 12 hours by air, so you'd have to carry 30 days' worth of food and water and a bed, at least, thus multiplying the deadweight needed to move one person from A to B. Sea freight is cheap, sea travel is expensive.

But I see the moral aspect of your argument. Families have no right to disperse themselves across the globe. If you are born in a cold, wet country, you should spend your holidays there. International cricket should be banned - televised computer games consume less energy. The Kenyan economy must revert to the stone age because transporting food from where it can be grown to where it can be eaten is a Bad Thing, and British people have no right to eat green vegetables in winter, or drink coffee at any time.  Life is not supposed to be enjoyable or even comfortable. Come to think of it, since people exhale 10% of all anthrpogenic carbon dioxide, and are indirectly responsible for the other 90%, human life should be exterminated. Plenty of other species will agree, though some human-specific bacteria would be severely discommoded.
Title: Re: Is this a stunning breakthrough in petrol engine thermal efficiency?
Post by: teragram on 30/10/2019 23:51:27
"Utter drivel. Airliners do not fly for the fun of it..."
But much of their payload does.

"The efficiency of jet engines approaches 60%"
But I understand that roughly half their power output is needed to overcome gravity.

"You could save a bit of fuel by using sea transport,.."
The energy consumption for air freight is 1.6 KWh/net tonne-Km, that for sea freight is 0.1 KWh/net tonne-Km. (published in 2009)

" Sea freight is cheap, sea travel is expensive."

At last, a glimmer of light!!...
Considering that "expense" is directly related to CO2 production. Remember my main point about discouraging long distance travel.

I realise though that air freighted food transport reduces CO2 by displacing the need for heated greenhouses in, the UK for example.

"British people have no right to drink coffee.."
I don't remember my history teachers telling me that Sir Walter Raleigh had to arrange air transport for his newly discovered coffee. (Sorry, I couldn't resist that)

 "Life is not supposed to be enjoyable or even comfortable"
Frequent long distance travel is not necessary for an enjoyable life, I can attest to that.
I think that we are very selfish to risk, by continuing our present lifestyle, condemning future generations to (far) less enjoyable or comfortable lives.

With respect, your comments on the possible future of the Kenyan economy and availability of green vegetables in the UK etc. mimic the protestations of climate change deniers over the last 30 years
Why single out the Kenyan economy? What about all the other poorer countries whose economies will be devastated by climate change? I've just watched a BBC news item about the drought in South Africa, particularly in an area where temperatures are rising by 2degrees more than the global average, and no rain has fallen for 5 years.

I don't think I implied that I wish to ban mechanised travel, or even air freight. Only that we should try much harder to improve the prospects for those who live after us.

Air travel is still rising, and predicted to keep rising for the coming decades. There seem to be no suggestions for achieving significant reductions in emissions, so we should be trying to reduce the number of passenger miles travelled. Perhaps you can understand my concern.
Title: Re: Is this a stunning breakthrough in petrol engine thermal efficiency?
Post by: alancalverd on 31/10/2019 08:19:05
Perhaps you can understand my concern.
Absolutely. Climate is changing (it always has), the human population will become unsustainable, and human aspiration will lead to all sorts of conflict.

Quote
I think that we are very selfish to risk, by continuing our present lifestyle, condemning future generations to (far) less enjoyable or comfortable lives.
Here's the rub. Our comfortable lives depend to a great extent on burning fossil fuel. There is insufficient renewable capacity to extend those comforts to everyone, but everyone wants them.

Ask yourself, what is the one variable over which we have complete understanding and control at no cost to anyone's immediate comfort, and which can increase per capita comfort in future?
Title: Re: Is this a stunning breakthrough in petrol engine thermal efficiency?
Post by: alancalverd on 31/10/2019 08:45:37
"You could save a bit of fuel by using sea transport,.."The energy consumption for air freight is 1.6 KWh/net tonne-Km, that for sea freight is 0.1 KWh/net tonne-Km. (published in 2009)" Sea freight is cheap, sea travel is expensive."

You seem to have missed the distinction between freight and travel.

Unlike a box of fruit, a sea passenger needs food, drink and a bed. For a 30 day trip from London to Capetown in any sort of comfort you would consume about 300 megajoules of food, about 300 liters of fresh water, and occupy a cabin consisting of about 2 tonnes of deadweight plus all the walkways and communal facilities (including lifeboats and airconditioning) that distinguish a passenger from cargo. If the passengers are not to be bored to death and start rioting you will probably need to add a piano, at least.

The only deadweight required for a 12 hour flight is a seat and a sandwich (2 kJ). Go to sleep, wake up and go to work.

Admittedly, lots of travel is unnecessary. So are lots of men.
Title: Re: Is this a stunning breakthrough in petrol engine thermal efficiency?
Post by: syhprum on 31/10/2019 15:48:30
As I tell my religious American friends god did not create mankind in his image for his glorification but as a food source for bacteria and viruses which is what he really loves.
Title: Re: Is this a stunning breakthrough in petrol engine thermal efficiency?
Post by: Colin2B on 31/10/2019 16:21:15
As I tell my religious American friends ....
So, how many of these friends do you have left??   ;D
Title: Re: Is this a stunning breakthrough in petrol engine thermal efficiency?
Post by: syhprum on 31/10/2019 19:00:27
They just tell me they will ask jesus to show me the light
Title: Re: Is this a stunning breakthrough in petrol engine thermal efficiency?
Post by: teragram on 09/11/2019 21:13:14
Climate is changing (it always has),

But the only relevant changes are those that have occurred since our species came into existence.

Our comfortable lives depend to a great extent on burning fossil fuel. There is insufficient renewable capacity to extend those comforts to everyone, but everyone wants them.

Therefore we should make every effort to not use fossil fuel wastefully. After all it takes something like 300 million years to make a litre of oil.



You seem to have missed the distinction between freight and travel.

I am aware of the distinction between freight and travel. I have been at pain to point out that huge amounts of fossil fuel are being consumed unnecessarily to move people great distances. I agree that travelling by sea is also wasteful of energy (unless passengers hitch a ride on a freighter that's going their way, quite common I think years ago). This has been my main point I think, since this discussion moved from advertising ethics. Maybe a partial solution would be palletised passengers. Come to think of it, that might go a long way to reduce the number of  passenger miles travelled!

Title: Re: Is this a stunning breakthrough in petrol engine thermal efficiency?
Post by: alancalverd on 09/11/2019 23:34:41
You could take the view that all travel is unnecessary, and it would be difficult to dispute that stance. Until 1802, nobody had ever travelled faster than a horse, and before the 20th century almost nobody had ever moved more than a day's walk from his place of birth. The brief spurt of human travel since the 1940s has certainly been a lot of fun but thanks to electronic communication, it's quicker and cheaper to phone or watch a webcam than to actually go there. But some of us enjoy it. By all means stay at home, but what right do you have to decide whether someone else's journey is legitimate? 

Sea passengers travelling on freighters still need all the deadweight of a bed, food, water, etc. And since very little sea freight moved before the 19th century, it could be argued that even that transport is unnecessary.

Most of what most people take for granted or aspire to, depends on burning fossil fuel. If you want to reduce its consumption, you have to change everyone's aspirations and expectations.  Walk to your candle-lit hospital when you are ill. Starve and/or freeze in winter, and spend your summer tending your hand-dug organic crops. It will solve the political problem of queues of lorries at Dover, since there won't be any lorries.

Meanwhile, for what it's worth, the prize for the first aeroplane to carry two people 100 miles in 1 hour on 1 gallon of fuel was won about 6 years ago. I'm saving up for one, just in case I really have to be somewhere else sometime.
Title: Re: Is this a stunning breakthrough in petrol engine thermal efficiency?
Post by: teragram on 13/11/2019 23:58:04
...but what right do you have to decide whether someone else's journey is legitimate? 
None at all. (Syhprum's friends might say "Judge not, lest ye be judged"). Nor do  I have the right to condemn future generations to floods, drought and starvation, by squandering valuable finite resources for my own recreational purposes.

Sea passengers travelling on freighters still need all the deadweight of a bed, food, water, etc.

But a few passengers travelling on a freighter, which is laden with thousands of tonnes of goods being transported at the most economical cost constitute a small part of the total weight.
And that weight does not have to be supported against gravity by burning fuel.

Walk to your candle-lit hospital when you are ill. Starve and/or freeze in winter, and spend your summer tending your hand-dug organic crops. It will solve the political problem of queues of lorries at Dover, since there won't be any lorries.

I don't think that ANY of my comments have suggested that fossil fuel use should have never been used, or should be banned now or in the future. I have tried to point out (ineffectively it seems) that profligacy in their use is leading to an early exhaustion of the resources at best, and a disastrous effect on the climate at worst.
To put it more simply, I do not suggest that people should not travel long distances, merely that they should do so (in some cases much) less frequently.

Meanwhile, for what it's worth, the prize for the first aeroplane to carry two people 100 miles in 1 hour on 1 gallon of fuel was won about 6 years ago. I'm saving up for one, just in case I really have to be somewhere else sometime.

Impressive, sounds like a genuine attempt to improve. Will it scale up to hundreds of passengers? How much more exciting though are projects such as NASA's X57 Electric Aeroplane.


Title: Re: Is this a stunning breakthrough in petrol engine thermal efficiency?
Post by: alancalverd on 14/11/2019 08:23:46
I do not suggest that people should not travel long distances, merely that they should do so (in some cases much) less frequently.
OK. Who, when?

About half of the passengers on any flight are travelling on business or other "legitimate" reasons. Passenger and luggage weight accounts for only about 20% of the takeoff weight of an aircraft, so if we ban holidaymakers and family reunions we save 10% of MTOW and about 2% of fuel, but probably bankrupt the airline.

Less than 7% of crude oil ends up as aviation fuel, so banning frivolous flying will save at best 0.14% of 30% of fossil fuel consumption (coal still accounts for about 60% and gas 10%).   

There are a few electric aircraft flying. Electrically propelled airships are interesting but of very limited application: if you've ever experienced a Force 9 on a boat, as you want your business travellers to endure, imagine the fun you can have in a weightless flexible ship moving in 3 dimensions! Electric airplanes fall into three categories: battery powered trainers (that rely on Russian gas to make the electricity to charge the battery) with about 1 hour endurance, solar-powered self-launching gliders and self-sustaining high altitude drones, and diesel- or turbine-powered hybrids. Unless battery technology advances by an order of magnitude, only the hybrid looks like taking off in a big way.
Title: Re: Is this a stunning breakthrough in petrol engine thermal efficiency?
Post by: teragram on 15/11/2019 19:55:18
... so banning frivolous flying...

When did I say we should BAN holidaymakers etc.? I repeat we have to REDUCE airline traffic.
And of course all other sources of ghg production, but road vehicle manufacturers seem to be more enthusiastic at moving forward (excuse the pun).
As for the 50% of passengers flying for business purposes, you yourself have frequently pointed out that people can conduct much of their work by electronic links.   
A new International Council on Clean Transportation (ICCT) report finds that aviation emissions are increasing 70% faster than UN projections that already point to a tripling of CO2 by 2050. In other words, the climate challenge for aviation is worse than expected.

imagine the fun you can have in a weightless flexible ship moving in 3 dimensions!

I thought that in the 1st half of the last century airships were the height of luxury in travel. I wondered though whether the lack of need for fuel to fight gravity would be offset by the large air drag caused by the size of the structure.

...battery powered trainers (that rely on Russian gas to make the electricity to charge the battery)...

Battery charging need not rely on Russian (or any other) gas, or coal, or nuclear power.

Title: Re: Is this a stunning breakthrough in petrol engine thermal efficiency?
Post by: alancalverd on 16/11/2019 08:19:41
A new International Council on Clean Transportation (ICCT) report finds that aviation emissions are increasing 70% faster than UN projections that already point to a tripling of CO2 by 2050. In other words, the climate challenge for aviation is worse than expected.
But still negligible compared with industrial and domestic heating, agriculture, human respiration, road transport....It currently accounts for about 2% of anthropogenic CO2. All your statistic shows is that the UN prediction was wrong.

"Fighting gravity" is an interesting point. An efficient glider needs about 5 horsepower (3.6 kW) to stay airborne with 2 crew at 60 mph. Roughly half of that power is dissipated as drag, so less than 1 kW per person is needed to fight gravity. Drag increases with the square of speed, so anything above 1 kW is ascribed to actually moving from A to B. Modern airliners are almost as efficient as gliders but clearly carry a lot more deadweight (toilets, galleys, luggage, unspent fuel...) so maybe expend about 5 - 10 kW per passenger fighting gravity and about 600 kW per passenger moving through the air. This is an interesting ratio: if you broke up the journey into short legs, so the takeoff fuel load was less at each stage, you wouldn't actually save much fuel, but in the light of this week's direct flight from London to Sydney it is worth considering whether air-to-air refuelling of airliners might be more efficient than intermediate stops: with half the initial fuel load you could probably carry twice as many passengers.
Title: Re: Is this a stunning breakthrough in petrol engine thermal efficiency?
Post by: syhprum on 16/11/2019 22:37:40
 "air-to-air refuelling of airliners" would make for a bit of excitement on an otherwise boring trip but I wonder about the economics.
Title: Re: Is this a stunning breakthrough in petrol engine thermal efficiency?
Post by: alancalverd on 17/11/2019 01:55:59
I'm still thinking about  this. The problem is that you have to lift all the fuel for a journey at takeoff. For a 747 the full fuel load is around 400,000 lb. If you only took half of this, and refuelled halfway to your destination, you could carry an additional 200,000 lb of payload - almost doubling your profit!

The additional cost would be that of flying a tanker for maybe an hour. But unlike a normal refuelling stop, you wouldn't have to disembark passengers and faff about with security etc, so the handling fees and time on the ground for the tanker would be much less than for a passenger liner. The tanker wouldn't need to be based at a customs airport at all - it could fly from a company site or a military base. Unlike combat refuelling you can take your time and choose your rendezvous "somewhere quiet".  It's a potential earner for countries that are overflown by long routes,  without the need to increase their passenger handling capacity.
Title: Re: Is this a stunning breakthrough in petrol engine thermal efficiency?
Post by: syhprum on 17/11/2019 21:06:07
Maybe flying into London from Japan you could refuel over Iran if you could solve the political problems
Title: Re: Is this a stunning breakthrough in petrol engine thermal efficiency?
Post by: alancalverd on 17/11/2019 23:24:01
It's not such a crazy idea!

The fun with military refuelling is that you are usually trying to fly a small,  fast plane (fighter) in the wake of a big slow one (KC135 - ish) - all very unstable. But flying a 747 in the wake of a tanker would be a lot easier - much more inertia and a better performance match at 500 mph.

London-Tokyo is normally by polar route. No political problem.  The tanker base would be an interesting posting somewhere in the Arctic Circle.

This actually shows the advantage of air travel over rail! There is a serious Russian proposal for a direct rail link between London and Tokyo, but the only feasible route is about 8000 miles - 2 days by the fastest possible train, maybe 4 days by something that can cope reliably with all the weather and track conditions, and a vast carbon footprint in steel and concrete, not to mention the disruption of other transport and migration routes. By contrast, the 6000 mile 12 hour polar flight already goes several times a day with no infrastructure or surface disruption at all. Refuelling somewhere over Russia would halve the fuel consumption per passenger.
Title: Re: Is this a stunning breakthrough in petrol engine thermal efficiency?
Post by: syhprum on 18/11/2019 13:15:27
`Although this would seem to offer economic advantages we must look to the example of the A380 which proved to be a failure be cause it was to big to fill up.
How would the extra load carrying capacity be used I can only think for freight if there was a need which would surely slow down the turn round time for the aircraft with loss of revenue.
As for aircraft taking a polar route from Japan to the UK let me recount my experience flying in from Korea we were scheduled to make a refuelling stop at Frankfurt taking a more southerly route (probably due to the promise of a favourable jet stream ) which took us along at a ground speed of 750 mph and made a Frankfurt stop not needed.
Title: Re: Is this a stunning breakthrough in petrol engine thermal efficiency?
Post by: alancalverd on 18/11/2019 23:13:04
Every time I've flown on a 380 it's been full. Pilot friends say it is a delight to fly. The problem is that very few airports can handle it (it's BIG) and its fuel efficiency has been surpassed by the Dreamliner with pretty much the same range - more profit per seat and a smaller capital risk.

If you start with a clean sheet and design for airborne refuelling, you will end up with an even more efficient machine than the 787. Everything that flies is a box of compromises: if you reduce the takeoff weight for a given range, you have an extra degree of freedom in your design.  Hence the military value - more payload, faster, more agile, or just smaller and more fuel efficient….
Title: Re: Is this a stunning breakthrough in petrol engine thermal efficiency?
Post by: teragram on 20/11/2019 23:35:32
All your statistic shows is that the UN prediction was wrong.

In that it was too optimistic?

Modern airliners are almost as efficient as gliders but clearly carry a lot more deadweight (toilets, galleys, luggage, unspent fuel...) so maybe expend about 5 - 10 kW per passenger fighting gravity and about 600 kW per passenger moving through the air.

It seems that the total drag on an aircraft is the sum of the drag due to it's frontal area and the induced drag, which is the result of deflecting airflow downwards to support the aircraft's weight. The former obviously increases with airspeed, while the latter decreases with airspeed. The optimum speed of the aircraft (in terms of energy required) is that at which the two quantities are approximately  equal. At this speed, the energy required to move forward is nearly equal to that required to maintain altitude. This is explained in:-

Sustainable Energy - without the hot air         David JC MacKay

 In "C  Planes II, page 269, available online.


Title: Re: Is this a stunning breakthrough in petrol engine thermal efficiency?
Post by: alancalverd on 21/11/2019 12:02:28
Not quite. Whilst the induced drag coefficient decreases with the inverse square of speed, drag force increases with the square of lift, which is proportional to the square of speed. Thus the drag force increases with the square of speed, and as power = speed x force, the power required to move through the air increases with V3.

"Optimum speed" is a lot more complicated. Propeller planes are most efficient at low speed and altitude, but the fuel consumption of a jet at idle or taxi is pretty much the same as at Mach 0.8 and 30,000 ft. Then there's the problem of flying in the corner between stalling and exceeding Mach1 at high altitude. Plus wind: no point in flying at 60 kt into a 100 kt headwind: however efficient your Piper Cub, it will go backwards! It's not much simpler with a glider: since low-level air is always rising and falling, you want to fly slower in rising air (allowing for wind!) and faster in descending air -  counterintuitive (because the induced drag wall make you descend quicker) but a lifesaver if you get the equation right.
Title: Re: Is this a stunning breakthrough in petrol engine thermal efficiency?
Post by: teragram on 02/12/2019 20:39:55
Thanks for the information, a bit over my head (pun intended), but what then is the ratio of lift power to drag power in level flight at the most economical speed? Given perhaps that conditions are perfect.

Title: Re: Is this a stunning breakthrough in petrol engine thermal efficiency?
Post by: alancalverd on 02/12/2019 22:00:40
Defining "most economical speed" is the problem.

There is a speed at which the lift/drag ratio is optimised and this will give you the least power required to stay airborne, but that won't be the maximum range for a given fuel load, or the min fuel for a given destination. As an example, consider a basic trainer like a Cessna 152 ( I just happen to have the flight manual on my desk at the moment!) With a full fuel load at 6000 ft it can fly about 700 miles at 45% power, 80 kt (best L/D speed) or 650 miles at 55% power, 90 kt,  in zero wind. But if we fly into a 30 kt headwind we can only go about 435 miles at either speed - it just takes 1.5 hours longer at 80 kt!

Since the upper winds can be in excess of 100 kt in any direction, and airliner operation depends on moving stuff from A to B, not just keeping it in the air, it isn't always best to fly at optimum L/D. Typically, an airliner will be designed to cruise at around Mach 0.8 (530 kt)  but the best glide speed (max L/D) is a lot lower - around 200 kt, and unlike a piston engine, a jet is more fuel-efficient at higher speeds.