Naked Science Forum

Non Life Sciences => Technology => Topic started by: Petrochemicals on 10/01/2019 12:47:17

Title: Could diesel be made clean?
Post by: Petrochemicals on 10/01/2019 12:47:17
Not counting efficiency, could the diesil engine be made clean ? Deisel engines where initially used for there high torque output espexially at the low end of engine rpm compared to petrol engines, lorries buses tractors etc used them as they provide lots of slow constant power. It is only in recent years diesils heve become popular because the fuel takes less energy to create ie refine and is more efficient and given that turbo diesils have developed, they also now give higher acceleration, somewhere near that of petrol engines. We have all been told by different mechanisms to buy deisels and then not to, yet it doesnt seem that we will be getting rid of large diesil vehicles any time soon, as even though a bus could run off petrol, it is likely that the efficiency versus the present diesil engine would be far far below the efficiency of having a bus with a diesil engine and that means citys and motorway avenues full of dioxins from diesil.

Unfortunatley as anyone with a brian and a bit of experience could have told the governments of earth before they started pushing diesils,  what comes out of a diesil exaust is very very toxic. Is there any reasonable way to process the exaust gasses such as reburning the exaust ( efficiency not withstanding) whilst the vehicle remains largely as mobile and as maintainance free as prior to modification.
Title: Re: Could diesel be made clean?
Post by: Bored chemist on 10/01/2019 12:51:34
Is there any reasonable way to process the exaust gasses
Yes.
https://en.wikipedia.org/wiki/Diesel_particulate_filter

On an unrelated note, do you know that some web browsers contain a spelling checker?
Title: Re: Could diesel be made clean?
Post by: alancalverd on 10/01/2019 14:21:19
Diesel exhaust can in principle be much cleaner than petrol exhaust as the initial combustion phase is more complete and the exhaust temperature is fairly constant so you can clean it up with catalysts. The problem is that the peak efficiency is limited to a fairly narrow speed range, which is why trucks have as many as 24 gears - the engine speed may be limited to 950 rpm idle and 1200 rpm maximum.

This isn't a problem on ships, where you can run a huge stratified-charge engine for several weeks at 120 rpm, and may be an advantage in future aircraft running a small turbine at 10,000 rpm and delivering thrust via contrarotating electric propellors. My hope is that someone (I'm too old to start the project now) will produce a diesel-electric drive train for cars with a 100 HP diesel running at 2500 rpm charging a battery for overtaking (150 - 200 HP delivered to short-term overdriven electric motors) and town driving (diesel off, 25 HP from the battery) with 80 HP cruise power available, so the diesel is either at optimum power setting or off.

The best thing to to with government advice, whether on wind power, salt, fat, or diesel emission,  is to ignore it.
Title: Re: Could diesil be made clean ?
Post by: Petrochemicals on 10/01/2019 19:56:30
Is there any reasonable way to process the exaust gasses
Yes.
https://en.wikipedia.org/wiki/Diesel_particulate_filter

On an unrelated note, do you know that some web browsers contain a spelling checker?
Diesel Diesel Diesel Diesel Diesel Diesel Diesel Diesel Diesel Diesel Diesel Diesel Diesel Diesel Diesel Diesel Diesel Diesel Diesel Diesel Diesel Diesel Diesel Diesel Diesel Diesel Diesel Diesel Diesel Diesel Diesel Diesel Diesel Diesel Diesel Diesel Diesel Diesel Diesel Diesel Deisel

The filter does not remove all particles, leaving the smallest most dangerous there, being the smallest there will be more particles per quantity too. And filters soon become blocked. With it being a fuel oil too, there are more pollutants in the mix than petrol.
Title: Re: Could diesel be made clean?
Post by: alancalverd on 12/01/2019 10:21:14
At least one manufacturer (Saab) has demonstrated that the exhaust from an optimised diesel engine was cleaner than the city air it was breathing in.

All flters can get blocked but a modern DPF has an automatic  cleaning cycle that oxidises the deposits or flags up its condition if it can't be cleaned. This resolves the particulates problem for cars and trucks, which occasionally travel long distances at high speeds (when the DPF can get hot enough to clean itself) but probably not for city buses and taxis. Sadly, our lords and masters seem keen to prevent cars and trucks from entering their domains, and to promote the public transport that causes the problem.
Title: Re: Could diesel be made clean?
Post by: chris on 12/01/2019 11:21:07
Diesel exhaust can in principle be much cleaner than petrol exhaust as the initial combustion phase is more complete and the exhaust temperature is fairly constant so you can clean it up with catalysts. The problem is that the peak efficiency is limited to a fairly narrow speed range, which is why trucks have as many as 24 gears - the engine speed may be limited to 950 rpm idle and 1200 rpm maximum.

This isn't a problem on ships, where you can run a huge stratified-charge engine for several weeks at 120 rpm, and may be an advantage in future aircraft running a small turbine at 10,000 rpm and delivering thrust via contrarotating electric propellors. My hope is that someone (I'm too old to start the project now) will produce a diesel-electric drive train for cars with a 100 HP diesel running at 2500 rpm charging a battery for overtaking (150 - 200 HP delivered to short-term overdriven electric motors) and town driving (diesel off, 25 HP from the battery) with 80 HP cruise power available, so the diesel is either at optimum power setting or off.

The best thing to to with government advice, whether on wind power, salt, fat, or diesel emission,  is to ignore it.

Very interesting post @alancalverd

You refer to drive trains for cars based on a diesel electric hybrid principle. You might recall we covered a similar technology for London's ageing bus fleet:
https://www.thenakedscientists.com/articles/interviews/hybrid-buses-are-coming-london
Title: Re: Could diesel be made clean?
Post by: Petrochemicals on 14/01/2019 21:48:15
AlanCalvert heve you a link on this please, as i cannot seem to find one.

The city bus link only states the better mpg because of no idling, so does this mean significant losses in the conversion to electric.
Title: Re: Could diesel be made clean?
Post by: alancalverd on 14/01/2019 23:13:04
Nothing more detailed from me, I'm afraid, but I think the transcript was a bit inexplicit. The trick he explained was that the diesel engine is either running at peak efficiency or switched off, but without actual figures it's difficult to see if the system could be extended as I suggested to deliver short-term overpowering of the electric motor. This probably isn't necessary for a city bus, which has a limited speed range and doesn't need to overtake anything faster than a bicycle.

Title: Re: Could diesel be made clean?
Post by: Galaser on 24/01/2019 01:17:39
Looking forward to one.
Title: Re: Could diesel be made clean?
Post by: nekS576 on 25/01/2019 14:58:03
I'm waiting for it
Title: Re: Could diesel be made clean?
Post by: Petrochemicals on 07/05/2019 10:30:00
https://patents.justia.com/patent/3952507

Could something like this be used to burn all the unburned fuel, or would the particulates be too small or inconbustable.
Title: Re: Could diesel be made clean?
Post by: alancalverd on 08/05/2019 08:41:04
A bit more complicated than just using a catalyst and recovering the heat energy with thermocouples, and returning zsecondary combustion products to the carburetor will surely reduce the efficiency of the primary engine?   
Title: Re: Could diesel be made clean?
Post by: Petrochemicals on 09/05/2019 11:47:04
A bit more complicated than just using a catalyst and recovering the heat energy with thermocouples, and returning zsecondary combustion products to the carburetor will surely reduce the efficiency of the primary engine?   
Well the lowering of efficiency is acceptable to a point. The diesil engine is superbly efficient as compared to the petrol engine in high torque situations, seriously something like twice or more than petrol,  so even if they lowered the efficiency by 25 percent to have clean air you would be quids in.

I do not think it is a recirculation system, where only a portion of exaust is returned, its more like a secondary engine chamber, more air and therefore oxygen is taken in to the exaust system and an attempt at ignition takes place, i should think that most of the particulates are partially combusted material, so new oxygen would be needed. I was thinking that the mixture may be too dilute for ignition by that stage, or the particulates incombustable. If the problem is the fact that the diesel in the cylinders is expected to perform a function ?Even if you added a bit of super heated extra diesil to getting the ignition going this would be easily efficient enough for the bus and lorry application.
Title: Re: Could diesel be made clean?
Post by: teragram on 21/05/2019 23:32:14
A bit more complicated than just using a catalyst and recovering the heat energy with thermocouples, and returning zsecondary combustion products to the carburetor will surely reduce the efficiency of the primary engine?   

Carburetor??
Title: Re: Could diesel be made clean?
Post by: alancalverd on 22/05/2019 18:21:24
If you have combustible particles in the exhaust you should have run the engine slower, with more oxygen!
Title: Re: Could diesel be made clean?
Post by: teragram on 05/06/2019 23:58:17
My hope is that someone (I'm too old to start the project now) will produce a diesel-electric drive train for cars with a 100 HP diesel running at 2500 rpm charging a battery for overtaking (150 - 200 HP delivered to short-term overdriven electric motors) and town driving (diesel off, 25 HP from the battery) with 80 HP cruise power available, so the diesel is either at optimum power setting or off.

Why a "short term overdriven electric motor"? The average electric vehicle has an electric motor which very capably copes with all running conditions, cruising, acceleration, town traffic...The best situation is an electric car with an engine used only for charging the battery. The engine can then be run at a constant speed corresponding to it's maximum efficiency, something in fact like the BMW i3 with "range extender", although this is a petrol engine. Electric motors are far better at moving vehicles than piston engines.
Incidentally (my apologies for being picky) diesel engines do not have a carburettor.
On second thoughts, the "best solution" is not to have a heat engine at all.
Title: Re: Could diesel be made clean?
Post by: Bored chemist on 06/06/2019 07:44:34
Obviously, all this depends on the definition of "clean".
Teh production of CO2 is still a problem.
Title: Re: Could diesel be made clean?
Post by: Petrochemicals on 27/06/2019 03:37:57
Obviously, all this depends on the definition of "clean".
Teh production of CO2 is still a problem.
Weve been through this before, co2 is not the problem its water vapour heating the earth !