The Bigger Bang: Diesel or Petrol? --Research

[Rosstorpedo]

Users of Motorsport Forums! This is the first time I have used a forum of any sort, so please pardon me if anything about this post seems peculiar. I have been involved in a research project at school; my topic has been the use of diesel engines in motorsport. I am now looking for feedback on an article that I have made briefly summarizing my findings. Any and all comments are helpful and appreciated.


Ross Carlson
The Bigger Bang: Diesel or Petrol?

For years, the automotive world has been centralized around increasing performance, and increasing efficiency. Recently, automotive manufacturers have been using new technologies to aid in these fields. It’s fair to say that nearly everyone knows the impeccable fuel mileage that the Toyota Prius is capable of attaining, and in Formula One, the amount of power produced per liter is the highest it’s ever been, despite the many regulations imposed by the Federation Internationale de l’Automobile. However, this industry has also been constructed upon the foundation of one particular fuel: petrol. For many years, automotive manufacturers have been producing diesel powered cars, often these cars were considered a inferior to petrol powered cars; they were heavy, slow, loud, and smelly. Luckily, technology has reduced these rather annoying properties to a quite tolerable level. Today about a third of all cars in Europe are diesel powered, and for a good reason. The Volkswagen Polo, sold in Europe, is capable of 99 miles to the gallon, a stunning feat; the most fuel efficient petrol powered car, the Kia Rio, is only capable of reaching 88 miles per gallon. So with this profound difference in the regular automotive sector, what new occurrences have come about in the performance sector?

To answer the previous question simply, diesels haven’t been especially revolutionary in motorsport. In recent years the Audi R18 has provided an interesting prospective at Le Mans, placing very high in the ranks, and even winning some races. Earlier in 2009 Volkswagen’s Touareg won the DAKAR series in Argentina.

What it comes down to is three things, more energetic fuel (high specific energy), more favorable power and torque bands, and safety.

The safety of each fuel can be determined based on the flashpoints. Diesel fuel does not burn unless it is very hot. In the unfortunate event of a crash, one of the main concerns is that the driver and the cockpit remain free of fuel to prevent burns and other heat related injuries. Drivers already use fire retardant suits, and sensors will shut off valves to the well protected fuel tanks to prevent any chance of fire reaching the driver, however, in some cases fuel, in the engine compartment of the car, is still left over and can ignite outside of the engine. Firewalls prevent the fire from reaching the cabin, where the driver sits, but still poses a hazard. If diesel fuel were to be used, spilled fuel, and fuel left in the engine compartment would be less of an issue; the high flashpoint will not permit the diesel fuel to ignite in open air, increasing the driver’s safety by magnitudes. Diesel fuel is also less volatile, meaning it does not emit as many fumes as petrol. Fumes and vapors are much more likely to cause explosions than liquid fuel. You may have noticed that at gas stations, there is not only a fuel nozzle, but a vent pipe as well. In petrol cars, any shaking or increased temperature will likely evaporate some of the petrol and create pressure on the seal. This vent removes the fumes created by the shaking, and moves them into the large tanks beneath the station. Most diesel nozzles do not have this vent, this is because few diesel vapors are present in the tank - most is ambient air. When the tank is filled up, the air is expelled from the tank, into the surrounding area. The thicker composition of diesel fuel is less volatile and produces fewer fumes, so the risk of any fire and explosions is greatly reduced.

Looking further into diesel fuels’ high specific energy, figures for both diesel fuel and petrol can be compared. Gasoline, petrol, has a lower specific energy around 44.4 MJ/kg, this fuel uses smaller hydrocarbon chains, containing mostly paraffins, the chemicals present are C8H18, C4H10, C5H12O, and C9H12. These have only single bonds between the carbon atoms, and it is these bonds that supply the chemical potential energy. The more bonds broken during combustion, the more energetic the reaction. In diesel fuel, the specific energy is much higher, around 45.4 MJ/kg because the chains of hydrocarbons C12H23, along with some C10H20 and C15H28 are longer, and contain more covalent bonds between carbon atoms to break. These chemicals are high density and can be found in kerosene (C12H23), ether (C10H20), and castor oil (C15H28).

Power is force in relation to velocity, or work done divided by time, and is represented by and individual point on the torque band. It is found by multiplying torque by the rotational velocity at that point and a constant. However, the highest instance of torque is not necessarily the highest point of power. For example, if a simple lawnmower engine provides the most torque, around 30 ft lbs, at 2000rpm, and provides half as much torque, 15ft lbs, at 6000rpm, the latter instance provides more power in the system. 30*2000 < 15*6000, worked out, 60,000 < 90,000. What this does mean though, is that in any gear ratio, the engine will accelerate the car fastest, at the highest point of torque, but only for that gear. If the ratio is taken down, trading rotational speed for torque, the higher power will accelerate the car faster than the previous situation, even though the torque is less. To be clear, here is a comparison of a torque band, in yellow, from a VW 1.9L Turbo Diesel Engine (top) and a torque band, in blue, from an extremely similar VW 2.0L Turbo Diesel Engine (bottom).
[img]file:///C:/Users/Leslie/AppData/Local/Temp/msohtmlclip1/01/clip_image002.jpg[/img] [img]file:///C:/Users/Leslie/AppData/Local/Temp/msohtmlclip1/01/clip_image004.jpg[/img]

In both torque bands, it is seen that the max torque occurs around 1900 rpm, but the max power occurs at around 3000rpm, in blue on the 1.9L and in yellow on the 2.0L. The turbochargers used on each changes how much torque each engine produce. The turbocharger on the 1.9L engine applies more pressure on the piston during the intake stroke pushing more air into the cylinder, so more fuel can be injected, and therefore more power and torque can be produced.

The most favorable power curves have a very high mean power over a large range of rpm. Petrol engines tend to have a power curve that peaks at the max, but has a mean power that is very low. Diesel engines generally have a very level power curve through almost 50% of the curve, from 2200 rpm, to 3200 rpm out of the full range from 1000 to 3200 rpm. [img]file:///C:/Users/Leslie/AppData/Local/Temp/msohtmlclip1/01/clip_image006.jpg[/img][img]file:///C:/Users/Leslie/AppData/Local/Temp/msohtmlclip1/01/clip_image008.jpg[/img]The 2.0L VW petrol engine has a less favorable power curve as it peaks at around 5000 rpm. The equivalent usable curve is from 4200 rpm, to 5700 rpm from the entire curve from 2400 rpm to 6100 rpm, so the equivalent band only uses 40% of the total band. It is obvious that the area under the curve for the diesel this specific range is larger than the area under the curve for the petrol engine. However, the petrol engine has a major advantage over the diesel engine. Because the actual combustion of diesel fuel is less powerful than gasoline, the engine itself is not as powerful, and this shows in the magnitude of the bands. The peak power of the diesel is 63 kilowatts which is about 85 horsepower. The peak power of the petrol engine is 106 horsepower, about 79 kilowatts. The petrol engine is capable of achieving 20% more power than the diesel engine; an outstanding result.

Diesel Engines tend to have more favorable curves, but have a much smaller magnitude of power. Technically, the engine produces a higher mean value of power throughout the range of rpm, but in full stature, the peak power of diesel engines is much less than the peak power of petrol powered engines. Higher mean power is a very good attribute when constantly accelerating and decelerating on a very curvy rally circuit, but is useless when the goal is top speed on long straights.

There is also some error within the graphs, and what trends occur between manufacturers. These differentiations are caused by the different styles of other systems among engines. In this case, the data can be considered reasonable, but unreliable since the diesel charts being examined are industrial engines, not intended for performance use.

At the present time, petrol engines are more suitable for motorsport, however because the diesel engine is superior in principle, research and development should be conducted in order to advance its effectiveness. Informing amateur motorists of diesel fuel capabilities will lead to more efficient vehicles on the road in general, and will encourage the research and production of diesel engines for performance use. The science behind engine mechanics has been studied since the internal combustion engine was created, in all, it is very extensive, and elaborate, still today research is being conducted to determine what new capabilities the internal combustion will have, from high performance exotic fuels, to safety in the inevitable.


Images from:

Volkswagen. Marshall's Industrial Products. Rep. 2011. PDF. Specifications Marshall's Industrial - Volkswagen powersystems and components distributor for the UK. IMPCO Gas products Distributor

[Mark]

Greetings, how old are you? What course are you doing?

The images don't appear as we can't see your hard drive

[Rollo]

What it comes down to is three things, more energetic fuel (high specific energy), more favorable power and torque bands, and safety.

What it comes down to in Motorsport is one thing only. The best use of regulations.

Racing teams honestly couldn't actually give a rip what the regulations actually are, just as long as they're able to exploit the rules better than their competitors. Indianapolis has in the past used jet turbines, Formula One engines in 1986 had their turbos screwed up beyond 5, 6 and maybe 7 bar and were producing in excess of 1700bhp in qualifying trim, and the only reason that Audi and Peugeot are using diesels at Le Mans is because those sorts of engines happen to be the best mix of compromise and exploitation in the rules.

Actually the most efficient combustion engine ever put into a motor car is the gas-turbine-electric-hyrbrid in the Jaguar CX-75 concept. It's hideously expensive to produce but puts out 720bhp and 1600Nm of torque from an combustion engine which is smaller than the computer tower used to generate this post. A Toyota Pius has a thermal effiency of about 35% whilst Jaguar's CX-75 is good for 58% with the electric drivetrain approaching 95%.

At the present time, petrol engines are more suitable for motorsport

Really? At the 24 Hours of Le Mans diesels are more "suitable for motorsport" and this is evidenced by the fact that the top 5 spots in 2011 were all diesel powered cars and the outright distance record which was set in 2010 was also set by a diesel.

The car which is most "suitable for motorsport" is the car which wins the race. A Racing Car has a specific purpose, to win a motor race and every single car from 2nd place has failed in that purpose. That can and should be the only measure of suitability.

[Mark]

For years, the automotive world has been centralized around increasing performance, and increasing efficiency. Recently, automotive manufacturers have been using new technologies to aid in these fields. It’s fair to say that nearly everyone knows the impeccable fuel mileage that the Toyota Prius is capable of attaining

And that's it's complete nonsense. A lot of technology, not a massive MPG improvement.

, and in Formula One, the amount of power produced per liter is the highest it’s ever been, despite the many regulations imposed by the Federation Internationale de l’Automobile.

What do you mean despite? Are they trying to increase fuel consumption? Of course, not, but don't forget the engine freeze in all of this. And it's "litre".

However, this industry has also been constructed upon the foundation of one particular fuel: petrol. For many years, automotive manufacturers have been producing diesel powered cars, often these cars were considered a inferior to petrol powered cars; they were heavy, slow, loud, and smelly. Luckily, technology has reduced these rather annoying properties to a quite tolerable level.

Quite tolerable!? Haha, Diesel cars are pretty much on a par with petrol, if not better, tolerable is rather insulting don't you think. And out of date.

Today about a third of all cars in Europe are diesel powered, and for a good reason.

In the UK more diesel cars are sold than petrol, Same in France, don't know about the rest of Europe.

The Volkswagen Polo, sold in Europe, is capable of 99 miles to the gallon, a stunning feat;

It would be stunning, if it were true, it can't get anywhere near 99 miles to the gallon. Perhaps you are confusing it with the CO2 emissions of 99g/km.

the most fuel efficient petrol powered car, the Kia Rio, is only capable of reaching 88 miles per gallon.

That sounds highly suspicious, and indeed just plain wrong.

To answer the previous questionsimply, diesels haven’t been especially revolutionary in motorsport. In recent years the Audi R18 has provided an interesting prospective at Le Mans, placing very high in the ranks, and even winning some races. Earlier in 2009 Volkswagen’s Touareg won the DAKAR series in Argentina.

Even winning some races? Remember Le Mans is only one race per year, and it won it. This is extremely misleading.

What it comes down to is three things, more energetic fuel (high specific energy), more favorable power and torque bands, and safety.

You may have noticed that at gas stations

Petrol, Diesel and now 'gas', are you cooking your dinner or running your car?

BTW, decent article, just a bit of fun to be poked too

[D-Type]

An interesting piece but I think it misses a key point. rather than being "much higher" at 45.4 MJ/kg the specific energy of diesel fuel is virtually the same as petrol at 44.4 MJ/kg. The two figures are so close that they could well be reversed with slightly different formulations. The better fuel consumption in mpg or litres/1000km of diesel engines is simply down to its density.

Of more interest is that it is possible to run some diesel engines on organic fuels (the so-called "Bio diesel") making this a sustainable way forward for the internal combustion engine along with alcohol (methanol and ethanol) once the oil runs out.

[Rollo]

That sounds highly suspicious, and indeed just plain wrong.

It sounds highly suspicious, and indeed just plain wrong because it is:

Today about a third of all cars in Europe are diesel powered, and for a good reason. The Volkswagen Polo, sold in Europe, is capable of 99 miles to the gallon, a stunning feat; the most fuel efficient petrol powered car, the Kia Rio, is only capable of reaching 88 miles per gallon.

Not even Kia makes this claim:
New Kia Rio - Technical Specification | Kia Motors UK | Kia Motors UK

Kia's own figures say that the 1.1 CRDi Manual does indeed get 88mpg, but the letter D in CRDi indicates that it too is a diesel. The most efficient petrol car in the Rio line-up is the 1.25 Petrol Manual 1 & 1 Air at 56.5mpg.

[Mark]

Plus our learned friend would do well to remember that manufacturer quoted figures are impossible to achieve in real life driving conditions, or often anything close to them.

[Malbec]

Well I'm glad that after a decade and a bit of participation in Le Mans, having spend 100s of millions of $s Audi Diesel cars have finally started to see the odd win or two

One factor you haven't addressed is that Diesel engines are heavier than petrol as they need to withstand greater pressures and the effect this has on handling. Also Audi and Peugeot winning at Le Mans with Diesels is not necessarily an endorsement of the fuel type as the Le Mans committee has altered rules for years to favour non-petrol cars. Also, both those Diesel teams were proper manufacturer setups with huge budgets, something none of the petrol engined minnows had. In short the multiple championship winning Audis and Peugeots were astonishingly well designed cars and would probably have torn the opposition to shreds whether they'd used petrol or Diesel.

As for real world use, Diesels may produce less CO2 but they do produce one hell of a lot more particulates and other emissions than petrol. Particulate filters are a stopgap solution but in urban driving may never reach the temperature they need to burn them off. Also spilt petrol evaporates quickly, spilt Diesel leaves a small oil slick which causes a hazard for other roadusers, especially bikes.

[Mark]

BBC News - Smaller engines drive petrol revival Interesting article about the increasing use of small petrol engines, which are lessening the advantages of Diesel.

I'm still 3-4 years off changing my car, and I wonder at the time will it be better for me to get another Diesel, or a small turbo petrol engine?

[ioan]

BBC News - Smaller engines drive petrol revival Interesting article about the increasing use of small petrol engines, which are lessening the advantages of Diesel.

I'm still 3-4 years off changing my car, and I wonder at the time will it be better for me to get another Diesel, or a small turbo petrol engine?

A petrol turbo engine is cheaper than a diesel, on top of it diesel fuel is just as expensive as petrol if not more expensive.
The next car I'll get will have an electric engine or at least a hybrid with petrol engine.