[hcl123]

Originally Posted by Joe Taylor

I don't know where to begin...

Diesel doesn not "literally explode" inside the cylinder, it slow burns, hence the lower engine speeds. By contrast, petrol combustion is always a very short process even when ignited via compression rather than spark ignition. This is due to the volatility of petrol and is also the reason for the compression ratio limit.

Yes you are right, explode is a strong word... but there are 2 forms for diesels

Stratified charge compression ignition... occurs at the boundaries of your fuel air charge and has a propagating front, and in here depending on the characteristic of the initial flame front your diesel can be quite a slow burner compared with gasoline. Same of those old engines even had a Glow plug always on to facilitate this...

Homogeneous charge compression ignition (HCCI)... in here there is no flame front... sorry again, i know its a strong word, kind of explodes, that is, the air fuel charge simply ignites everywhere at the same time...

http://en.wikipedia.org/wiki/Homogen...ssion_ignition

this effect is hard to achieve and i don't know if that is the case of Audi or Peugeot diesels, but i'm not surprised if they managed to get that effect to some degree.

So diesel by being, lets say, more energetic having more time to burn than gasoline in a specific volume of fuel, but by having the charge mixture much more compacted and pressured and so much more mixed, if they achieve a good effect of HCCI, then i can bet you that the same volume of fuel burns faster in diesel mode than in a spark petrol mode : practically there isn't a flame front in HCCI modes

Originally Posted by Joe Taylor

compression ignition petrol engines can run to high compression ratios, the problem being that as the combustion is very short, the intake conditions need to be controlled precisely to avoid detonation or misfire.

Funny thing is that in experiments is much easier to achieve a HCCI mode in petrol than in diesel, specially because of the higher volatility of petrol that permits a more rapid homogeneous mixture of the air fuel charge... without the enormous pressures of fuel lines that common-rail diesels have... the problem is the temperature point of self ignition of petrol... the higher the CR the higher the specific temperature... so at top dead center TDC, the compression ratio must be substantially lower than what a diesel can achieve because petrol self ignites at much lower temperatures than diesel... and this even in a HCCI petrol engine.

In a way it has nothing to do with the pressure level... if it were possible to cool the air-petrol mixture while its being compressed, it could attain as higher compression ratios as diesel... with comparable fuel consumption and torque.

As that is not yet possible, so petrol engines must always have a "flame front", the reason for the spark plug being there... and race engines with always very rich fuel mixtures, are "slow burners" compared with diesels that can achieve an ignition comparable with a HCCI effect... and simply at 8 to 10K RPM there is not enough time to burn all that very rich fuel mixture inside the cylinder...

Originally Posted by Joe Taylor

The noise of petrol engined LMP cars has nothing to do with burning petrol in the exhaust (how could this happen anyway given petrol's short combustion time?) but is due to the items placed in the exhaust. The diesel LMPs are turbocharged, which has an effect in quietening the engine noise and the particulate filters further quieten the sound. It's worth noting that the Peugeot is now almost as loud as the turbocharged petrol LMPs after allegedly removing their FAP filter.

What the hell are those flames that came out of petrol engine cars, particularly well visible at night, and quite often, specially when the car brakes, and after YEARS of all constructors having electronic injection systems that cut fuel upon braking... does your car not do that ???... are those special items placed in the exhaust, a flammable substance tank, an artistic exuberance for the delight of all of us petrol heads ???

I bet its the contrary... its by being turbocharged, and reasonably well... that diesel engines are more loud than they could be... pressure along the exhaust is higher, but particulate filters, like sniper rifle silencers, has had quite a job of making them almost inaudibles... and perhaps is what happened with peugeot , no filter/silencer and the sound got much higher... but i never saw a flame came out of a diesel exhaust pipe...

Originally Posted by Joe Taylor

The diesels dominate LMP racing for 3 reasons: 1) they were given a massive advantage in the original regulations, 2) as diesel is a new technology to endurance racing, the development scope is greater, 3) factory teams always beat privateers due to their larger budgets allowing more development. Case in point, in 2009, the top petrol non-factory car was the ORECA, which completed 12 fewer laps than the winning diesel. In 2003 and 2004 against factory Audi supported opposition, the top privateers were 17 and 18 laps down respectively.

They where given a considerable start advantage in terms of max volume of displacement with turbo-charging addition. The rest they have been getting harsher and harsher penalties...

Reverse that... make everything equal....

I don't call it dominate... i call it crushing... there was a "oil-petrol" marketing campaign that went bad, happens often in all areas of activity... and in some way i advocate that the current situation is not funny for various parts involved... but the solution is not discriminate any kind of fuel tech by the way of very stupid distorted rules. Today constructors make multi-fuel engines more and more, and them tune them to a particular application...

Let the rules for a ICE engine be EQUAL, and let the teams choose the fuel type without mioptic forced downsizing, cripitic stupid restritores regulation, and others.

A Lemans car, prototypes included, must have place for 2 persons, and all cars must have road homologation and arrive at the "circuits" with those 2 persons ( one of the seats withdrawn for the race), from public roads by their own means, and so civil law must apply... petrol ( or diesel) noise must be only to a certain level permitted by law, filter/catalytic converters/ buffer silencers will be mandatories then, pollution emission regulations will also be mandatory. Then the constructors must make the best of an engine in any format( Otto, Wankel, rotary) up to a max of volume displacement no matter the fuel type... and restrictiors and weight EQUAL to all... according to the respective category.

And Kinetic recovery systems allowed in any form or tech... meaning only that the initial electric power density and or initial hydraulic tank pressure, should be exactly the same also.

Then finding out about a new prototipe like R18 will be much more fun... because they could decide to make something really exotic... and as hard this might sound, like with very small companies that are launching those techs in everyday cars, privateers could have more "guts" and launch simple and cheaper but clever exotic techs( by today standards) that might get them some luck.