Diesel vs Petrol

[387star]

Wondering why these trains can't be petrol powered is diesal preferred?

 

[starrymarkb]

Diesel was until recently cheaper then petrol, plus you don't use as much of it for a given engine size. You also don't need complex ignition systems, diesel ignites during the compression stroke

 

[asylumxl]

They have great thermal efficiency too, and in general diesel engines produce more torque for the same engine displacement.

 

[RobShipway]

Plus you can get more miles to the gallon with Diesel, even with the fact of better fule economies with petrol engines.

 

[jopsuk]

The same goes for road trucks, ships etc. Very few large petrol engines- I suppose the closest would be the large piston prop engines used in 40s/50s aircraft (though they tended to use much higher grade fuel than normal petrol).
Really, this is perhaps better in another thread- there's nothing special about the use of diesel in the 22x series.

 

[Jordy]

Split from http://railforums.co.uk/showthread.php?t=43486

 

[Oracle]

There have been petrol-electric railcars in the past, when compression-ignition engines were in their infancy. However, CI engines are much more efficient as has ben said. Diesel fuel used to be a by-product of petrol distallation and was cheaper than petrol. On the Continent, it still remains cheaper.

 

[387star]

What's torque I've heard that word before?

Yeah I've always wondered what the difference is (I don't drive) because both come from oil? The only difference is what happens to it once it enters the exhaust system>?

 

[Darandio]

http://en.wikipedia.org/wiki/Torque

That should either enlighten or baffle you.

 

[jopsuk]

The basic difference between petrol and diesel is that the hydrocarbon molecules in diesel are longer and therefore less volatile. It isn't quite that simple(!), but that'll do for now.

It helps to be careful with terminology- properly, "Diesel" refers to the engine type- one that burns fuel via the Diesel cycle- with "diesel" fuel being just one of the fuels they can on (modern car diesel engines are rather more restrictive in what they burn). Large ship engines will be "Diesel" but typically burn even heavier fuel oil.

One of the historic reasons for diesel being cheaper than petrol in this country, one that still applies in some countries, was that it was taxed less.

 

[Peter Mugridge]

Diesel fuel is a lot safer as well.

 

[rail-britain]

Diesel was until recently cheaper then petrol

At the trade rate, there isn't much difference now, but it is still cheaper when you are bulk buying

 

[merlodlliw]

What's torque I've heard that word before?

Yeah I've always wondered what the difference is (I don't drive) because both come from oil? The only difference is what happens to it once it enters the exhaust system>?

In easy words, if its 2 litre diesel you wont need to change gear so often while climbing, if its 2 litre petrol you will change more often.

While towing, the same applies but far more noticeable, LPG is even worse.
I drive all 3 types for colleagues, we have a diesel/LPG pick up, that's awful towing in LPG mode.

Bob

 

[moonrakerz]

Diesel fuel is a lot safer as well.

That reminds me of an incident some years back; two "experts" in the aviation world had a long running argument about the safety merits of two different types of aviation fuel.
Eventually the proponent of one type of fuel challenged his opponent to a "duel".

Each would stand in a large metal tray into which had been poured 10 gallons of "their" fuel. They would then take turns to strike and throw lighted matches at their opponent - there is no record of this challenge being taken up !!!

 

[LexyBoy]

Diesel engines are more efficient due to the higher compression ratio, which is the main reason you get much better mpg with Diesel - hence it's cheaper, even with diesel slightly more expensive by volume than petrol.

Petrol gives a more even power output & efficiency over a wider range of rpm - which is what you want with a car with mechanical transmission. OTOH, Diesel engines have a higher peak efficiency, but over a narrower range of rpm - not a problem for a train where the engine can run constantly at its ideal rpm (electric transmission). This is also the reason trucks (and diesel cars I think, don't know much about cars) have more gears than petrol.

Diesel engines are in principle simpler (though heavier) which probably also encouraged their adoption for large vehicles where performance and weight are not at such a premium. I expect that modern Diesel engines are not so simple any more though!

 

[jopsuk]

Diesel cars tend to have the same number of gears as petrol cars.

The fuel efficiency is the primary reason Audi (and I think now others) made the switch to diesel for endurance racing cars (Le Mans primarily)- less time spent fueling the car makes for more laps round the track. of course, they were also doing that as a way of demostrating that their diesel technology is good enough for even racing cars.

There's a lot of very good, well researched and referenced (and illusttrated) content on wikipedia regarding different engines and fuels, though much is quite technical.

 

[LE Greys]

If you want simple and light, go for a gas turbine. The simplest have one moving part, the turboshaft itself. Theoretically, they can run on diesel or petrol, but normally on a particular grade of kerosene. Thing is, they don't like spooling up and slowing down all the time, so they do not really work in something that runs at varied speeds.

According to family legend, my grandfather (the one who was a test pilot) sometimes used to fill his car up with aviation-grade petrol. It ran beautifully.

 

[90019]

If you want simple and light, go for a gas turbine. The simplest have one moving part, the turboshaft itself.

They're not particularly efficient though.

 

[WatcherZero]

In WW2 the Germans used Petrol powered tanks rather than diesel like everyone else, you can look up the problems that caused with underpowered engines that wouldnt work in cold weather or in wet environments.

 

[strange6]

Wondering why these trains can't be petrol powered is diesal preferred?

Diesel engines tend to have a much longer life as well as being far more robust. The main reason for a diesel engine in trucks and trains is the greater pulling power that they have (or in easier terms 'towing' power)

 

[Peter Mugridge]

According to family legend, my grandfather (the one who was a test pilot) sometimes used to fill his car up with aviation-grade petrol. It ran beautifully.

I can believe that - an aviation expert told me last year that the premium unleaded petrol currently available is not very much different from the old JP-4 aviation fuel.

Certainly my car runs much better with the premium petrol in it than with the regular stuff.

 

[ChrisCooper]

The main disadvantage of a diesel engine is it's low power-weight ratio, but in heavy vehicles this isn't a problem as the engine is only a fairly small proportion of the weight, and for heavy haulers the extra weight improves traction so a heavier engine just means less ballast. Same goes for ships and boats. The only other real problem with diesels is their cold start ability. Cars and other smaller diesels have glow plugs to warm the cylinders, but larger diesels don't (trains don't, buses and lorries don't), and they can be quite hard to start in the cold. Then again they will start eventually, as long as the batteries don't give up beforehand. I've known old diesel engines that have stood for years start up in below 0 conditions with a decent pair of batteries and a bit of patience, infact the only time I've known one not to start was because some idiot had turned the fuel valve off (despite being asked before and a few times during "is the fuel on?").
Diesels are also fairly bad for pollution. At low temperatures the heavy oil does not burn fully leading to soot and unburned hydrocarbons being emitted (along with various pleasureful emissions from watching enthusiasts), wheras at high temperatures nitrogen in the air is turned into nitrogen oxides. Modern engines and exhaust aftertreatment seriously improve both of these though. Then again, Petrol engines used to give out lead.

 

[starrymarkb]

If you want simple and light, go for a gas turbine. The simplest have one moving part, the turboshaft itself. Theoretically, they can run on diesel or petrol, but normally on a particular grade of kerosene. Thing is, they don't like spooling up and slowing down all the time, so they do not really work in something that runs at varied speeds.

According to family legend, my grandfather (the one who was a test pilot) sometimes used to fill his car up with aviation-grade petrol. It ran beautifully.

The French withdrew their GTMUs a few years ago in part because of the high fuel consumption.

Those who like big noisy things might like this
[youtube]J_ttLyApLIM[/youtube]

 

[ChrisCooper]

Such a shame none of the UK Gas Turbine locos were preserved. Great way to **** the neighbours off on diesel galas (buy a new house next to a preserved railway, what do you expect?). Funny how at speed they sound like a HST or other screechy turbo type (actually mostly get VP185 from it, as they tend to have a high pitched screech than the Valentas), but at low speed of standing it's more like a fighter jet. Then again, making that sort of noise, and knowing the reputation of GTs for very high power-weight ratio, I did expect a bit more lively performance.

Oh well, anyone fancy getting the APT-E running again.

In another world, where oil prices were lower, reserves higher, and less worry about the environment, I do wonder if we would have seen another generation of gas turbine powered Rail and Road vehicles emerging for high performance roles? With more development I'm sure efficiency could have been improved, and I'm sure a GT would work quite well as the generator on a modern hybrid system (constant power output, charging or being boosted by batteries as needed).

 

[starrymarkb]

Well those five coach trains are driven by two 1030hp gas turbines. With two smaller (400hp) ones for auxilleries. Fuel consumpton was high though

"Each turboengine was equipped with a 3500 litre diesel tank for use on long routes, with a consumption of 430 litres per hour for traction and 150 litres per hour for passenger comfort."

After withdrawal the journey from Lyon to Bordeaux lengthend by 90 mins (because being units they could reverse quickly at the 4 reversals on route - and the turbines were better on hills)

 

[CosherB]

In WW2 the Germans used Petrol powered tanks rather than diesel like everyone else, you can look up the problems that caused with underpowered engines that wouldnt work in cold weather or in wet environments.

The British Centurian tank used a RR Merlin petrol engine - the same V12 unit used by the Spitfire and Lancaster.
--- old post above --- --- new post below ---

I can believe that - an aviation expert told me last year that the premium unleaded petrol currently available is not very much different from the old JP-4 aviation fuel.

Err, no. JP-4 was a blend of kerosene and petrol used by the US Air Force. Kerosene (Jet A-1 aviation fuel) is effectively diesel fuel, or paraffin, or central heating fuel.

A petrol engine would not run on JP-4.

Aviation gasoline (petrol) used in aircraft piston engines was OK to use in cars of old. But do not use it in a modern car with a catalytic convertor. It has a very high lead content, and that will kill the cat. Your car will fail it's next MOT, and you will have to find several hundred pounds for a new cat!

 

[ainsworth74]

The British Centurian tank used a RR Merlin petrol engine

The M4 Sherman used a petrol engine as well as I recall, and it developed a reputation for catching fire very easily.

 

[Hydro]

The M4 Sherman used a petrol engine as well as I recall, and it developed a reputation for catching fire very easily.

A few American tanks got the nickname "Ronsons" because they were "guaranteed to light, every time". The Germans, rather more bluntly, called them "Tommy Cookers".

 

[ainsworth74]

A few American tanks got the nickname "Ronsons" because they were "guaranteed to light, every time". The Germans, rather more bluntly, called them "Tommy Cookers".

They got that German name during the African Campaign as I recall. Didn't know about that other one though. Never really been a fan of the M4 but it did a job so can't complain that much.

 

[Zoe]

Why don't cars do the same as many trains and have diesel engines supply power for electric traction motors. As full torque is available with these electric motors there wouldn't be any need to change gear.