Diesels at Le Mans 1

[PJGD]

I see that the first diesel-engined car to qualify and race at the 24 hour race at Le Mans was a French entry in 1949, the first race held after the war. The car was the Delettrez Diesel entered by brothers Jean and Jacques Delettrez and was of 4395 cc 6-cylinder. It did not finish, running out of fuel about half way into the race.

Delettrez entered again in 1950, as did another diesel car, the MAP. Again both cars DNF with engine problems, a cooling system leak in the case of the MAP. The MAP was interesting in that it was the first mid-enginesd car to race at Le Mans, the engine was located immediately behind the driver, and was a two-cylinder opposed piston 2-stroke with rocking levers connected to a single crank, similar to the later Commer TS3 engine. Many thanks to Aorangi for providing me with supporting information on this engine.

The Delettrez entered in 1951, for the last time, but again DNF due to the engine after only 4 hours.

My question(s): Has anyone got more information on these pioneer racing diesels? Have there been other diesel cars at Le Mans since then? How long before we see diesel cars at Le Mans again; any guesses?

PJGD

 

[Heptec]

On a slightly related note. Back in 1970 one of my neighbors was none other than George Cummins and he told me all kinds of stories about the Cummins Indy car but never said anything about Le Mans His storys usually ended up with "Dad finally said it was too Da-- expensive to keep the dust down using race engine parts and diesel" One unknown tidbit was that George claimed he was allergic to diesel fumes. Cummins may have some of the research data available
Wish I could help.

 

[TChronos]

FWIW, I have a few photos of the 1950 Le Mans. I posted the only photos I have of the Delettrez and MAP cars here:

http://community.webshots.com/scripts/misc.fcgi?action=invitePickup&uri=album/82949565SQllev

Hopefully, that link will work, otherwise I have to find a better place to post.

 

[PJGD]

TChronos:
Yes. that worked well. Thank you very much. Do you by chance also have photos of the Jowett Jupiters that ran (and won the 1.5 Litre class each year) in 1950, '51, and '52? If so, I would like to see those too!

PJGD

 

[kenvlach]

It’s unlikely that we shall see another diesel-powered racecar.

My opinion: Because of the mechanics of the combustion processes, diesel engines can’t rev as high as gasoline- or alcohol-powered engines. In the latter, the fuel is already vaporized and mixed with air when it enters the cylinder, plus the spark can be readily advanced in accordance with rpm. In a diesel engine, it takes some finite time for the injected liquid fuel to spread across the cylinder, absorb heat, vaporize and then absorb some more heat to the point of self-ignition. Of course, the injection can be advanced with rpm and the fuel pressure can be increased, but I have a strong hunch that diesels have a lower max. rpm and hence HP limit.

Anyone know what are the fastest-revving diesels?
Ken

 

[TChronos]

I came across an interesting article discussing what would be required in a Le Mans Diesel engine, from a technical perspective:

http://www.totalmotorsport.com/Features/Technical/Display.asp?ID=1

Diesels are permitted under current ACO rules, in fact, there are special amendments to cover them. I think there was a privateer team in the last race that ran Diesel.

PGD:
Yes, I think I have photos of the Jowetts, I'll post them later if I find them.

 

[kenvlach]

Thanks, TChronos.

The Totalmotorsport article is very informative. It indicates 3 limiting factors to diesel engine rpm:
1) constant flame burning rate (as I posited above),
2) greater volume of air needed for same fuel energy (turbocharging was suggested),
3) heavier mass of engine parts due to 1.5x combustion pressure. Obviously a problem with reciprocating parts and bearings. One point of the article was that the winning required engine durability.

"Then again, the engine is heavier as the maximum power revs would be only around 5 000...6 000 per minute, whereas spark ignited engines can have it up to 10 000 rpm or so. So the load per cycle of a diesel engine is 10 000 / 6 000 = ..appr. 150% of that of a petrol engine of similar power. Therefore the components in a diesel need to be beefed up a lot = heavy engine. In a diesel, revs cannot be upped very easily as the constant pressure burning in the combustion chamber simply takes its time."

http://www.totalmotorsport.com/Features/Technical/Display.asp?ID=1

 

[PJGD]

An interesting analysis; thanks TChronos.

I cannot however agree with the comments suggesting that diesels are limited due to "constant pressure combustion" (the totalmotorsport.com article), or by "constant flame burning rate" (kenvlach above). Constant pressure combustion was the theory back in the very early days of compression ignition engines, but it is not like that with the high speed engines we are contemplating here. It is somewhere between that and constant volume combustion.

Just as in SI engines, flame speed can be influenced by appropriate air motion (turbulence, tumble etc), so air motion (typically swirl) can be used in diesels to modulate the rate of air entrainment and thus the rate of heat release. The rate of injection is another factor that has very strong influence on the rate of heat release, and this is achieved through raising (or lowering) the injection pressure. Within limits, this is a tuneable feature with modern common rail and unit injector fuel systems. As mentioned in the article, engine power is typically peak cylinder pressure limited in structural terms for CI engines, which corresponds to the detonation limit seen by SI engines.

While it may be that a BMW V8 diesel may appear at Le Mans in the near future, I am not convinced that it would be a good basis for a high performance engine. With the availability of modern high pressure fuel injection systems, passenger car diesels moved from divided chamber IDI combustion systems (typically the Ricardo Comet Mk.V), to 4-valve central vertical injector bowl-in-piston DI combustion systems to pick up the benefit of better fuel consumption and higher thermal loading capability. This translated into the sort of power outputs when turbocharged which made the engines comparable to current SI engines (on the order of 55 kW/litre). But bowl-in-piston pistons are very heavy and not well suited to high engine speeds, and the combustion system is very dependant on escalation of injection pressure for future power growth. My view is that there is still room for growth in divided chamber combustion systems if higher engine speeds are believed to be the way to go; the piston is much lighter, and the combustion system has more potential for rapid combustion. I also think the thermal loading issues are solvable. However, this is not the direction that the industry is moving in, so such an engine is not likely to be seen at the Sarthe.

PJGD

 

[tdirs1]

I would have thought the obvious choice for a le mans engine would be the VW V10 tdi,this develops over 300hp and 750nm of torque!! Why would you have to make a diesel high revving to be competitive? I dont think you do my own 1.9tdi Golf devolops 224hp flywheel and 204.5hp wheel and 480nm of torque with the right gear ratios it would do 160 mph!! If the engine doesnt rev but produce huge amounts of torque,then the right gear ratios would be the answer not making the engine rev beyond its design.

 

[GregLocock]

How do you work that out? Ballpark figure for hatches is 100 hp for 100 mph, and you are mostly fighting a cube law, ie you'd need in excess of 300 hp for 160 mph. My performance predictor for a Prius says it'd need 340 hp at the engine.

I mean, we are talking engineering here aren't we?



Cheers

Greg Locock

 

[ruble3]

been following the discussion & remember seeing somethimg in Toronto Globe & Mail a few months ago about new diesel technology- may not apply to leMans but is interesting anyway- will certainly have many applications, especially in my field ( assuming it proves out- its about a company called Westport Innovations ( I have absolutely no connection to the company- no shares etc) - just thought you may be interested in the article ( if you look at Wesport's website the Globe & mail article is there)

 

[PJGD]

Direct injection of gaseous fuels is the way to go, if you can do it. The Westport system is good, somewhat complex, and certainly expensive, but they are leaders in their field. As applied to CI engines though, it is essentially a gaseous engine with diesel pilot, ie, under load 90% of the fuel burned is whatever gas you are using, and 10% is diesel fuel which acts as the ignition source for the gas.

I doubt that we will see an engine like this at Le Mans.

PJGD

 

[tdirs1]

Guess your predictor is for a petrol engine not a diesel!!

 

[tdirs1]

Audi are entering a diesel powered racecar at the next Le mans!!

 

[PJGD]

That is most interesting. I will look forward to reading the articles about this initiative and how people "justify" using a diesel. Personally, I think that this is good for the diesel industry; We need the product development that comes through competition on the race track. SI engines have had the benefit of this for years; now perhaps the diesel can get a "boost" from it. Will be interesting to see how it does relative to the Totalmotorsport article.

PJGD

 

[aorangi]

PJGD,
Sorry I hadn't seen this interesting thread before !

Your paragraph...
"My view is that there is still room for growth in divided chamber combustion systems if higher engine speeds are believed to be the way to go; the piston is much lighter, and the combustion system has more potential for rapid combustion. "

...remained me of the SEMT-Pielstick PA 4 with variable geometry pre-chamber, a system which seems to combine the advantages of direct and indirect inject.

http://www.pielstick.com/frRail.html

and then click on High speed diesel engines to find a picture of the combustion chamber.

What do you think of that ? I had some more documents about it, but I was unable to find them right now. Looks like I've lost them.

Cheers
Aorangi

 

[zeitghost]

It's off topic, but one of the most powerful piston aero engines was the Napier Lion.

This was a horizontally opposed, compounded diesel engine.

In development, they realised that more power would be available if the remaining oxygen in the exhaust was used to provide more thrust from an afterburner.

Eventually someone came to the conclusion that they would end up using the piston engine as a gas generator, essentially reinventing the jet engine with a lot of unnecessary complications.

 

[aorangi]

Yes, the famous Napier Nomad (the Lion was a pre-war spark ignited W12 with 3 banks of 4 cylinders). It's been talked about on thread thread71-63511 and thread71-48738 in which the gas generator principle was also mentioned. I think the gas generator concept would have been more suitable for automotive then pure gas turbine since its efficiency can be somewhat higher in that size range, although not as good as that of a turbocharged diesel, especially under part and low load.

Perhaps a turbocompound 2-stroke opposed pistons diesel would be fine for racing. In the extreme case, when all the power of the diesel is used to drive the compressor, it becomes a gas generator. Any point in between the conventional diesel and the gas generator can be obtained with turbocompound differential supercharging such as in the Geislinger locomotives.

Cheers
Aorangi

 

[zeitghost]

Grovelling apology!

I've just found LJK Setright's book "Turbocharging and Supercharging for maximum torque and power".

Part of Chapter Eight describes the Napier Nomad, with cutaway diagram.

Complex is not the word for it!

rgds
Zeit.

 

[PJGD]

Aorangi:
I appreciate the link to the Pielstik PA-4 engine; I had not seen that before but can see that it has some valuable features.

On the compression stroke, without the obturator (or piston poker) in the way, there is little restriction involved in pushing the air into the pre-chamber. This is a significant advantage over the conventional fixed geometry pre-chamber designs which loose some efficiency to the pumping losses involved. However, I do not see anything which would give the air a controlled motion once it is in the pre-chamber. That is to say, it is a true pre-combustion chamber and not a swirl-chamber, since there is nothing to generate the (rotational) swirl. This too is an energy savings, since it takes energy to create the rapid air motion. It does however mean that the nozzle may have to be a bit special since instead of having the air presented to the single spray plume as is the case for a swirl-chamber, the fuel now has to find as much of the randomly turbulent air as it can - and this suggests a multi-hole nozzle? Even though this design still has a large combustion chamber surface-to-volume ratio, similar to other divided chamber engines, the apparent lack of swirl will also help to reduce heat loss to the coolant and thus maintain high efficiencies.

After the start of injection, it is possible that the "uncooled" obturator now projecting into the pre-chamber, plays a role in initiating ignition. But whatever: following ignition and as the pressure starts to rise in the pre-chamber, partially burned elements will be forced out of the pre-chamber and into the main chamber through a restricted annular orifice and, taking direction from the radiused profile on the obturator they will be directed across the chamber into the valve pocket areas above the piston where the remaining air is to be found. This too seems like a relatively low energy loss geometry compared to a fixed geometry chamber, since as soon as the piston begins to descend, the orifice opens up once again.

I do however have concerns about the concept as it might be applied to automotive engines which must address stringent emission standards. Such engines, to achieve reasonable engine-out NOx levels, are obliged to operate at relatively retarded injection timings very close to TDC, and with extended injection durations to keep bulk gas temperatures down. This would likely require a much longer obturator (since the piston is now further down the bore) than the 1,500 rev/min rated Pielstik engine exhibits, and this might be a durability issue. Nevertheless, on a first look, this chamber concept has much to commend it.

Thanks Aorangi!

PJGD