differences between diesel and gasoline fuel

[silver343124]

hi.

I was wondering what will happen if we will try to run diesel cycle engine on gasoline?

I know how both otto and diesel cycle works, but I gues that main difference between diesel and gasoline (beside other physical properties) fuel is its speed of burning.
I am guesing that diesel has longer carbon-hydrogen molecules than gasoline, so it is burning slower, that is why diesels have longer stroke and slower rpm.

So hypoteticaly (or from experience if enywhone has try it), what will happen if we run diesel engine on gasoline. I'll say that gasoline will burn when injected to the cylinder, but propably the explosion and temperature will be to high and the peak pressure will eventualy damage the egine.

On the other hand what will happen if we run gasoline engine on diesel. Probably nothing as there will be misfires and even egnited diesel won't burn efficently, so I'll say engine won't even run.

(But once by mistake I fill the lawn mowe with the diesel and it ran for about few seconds or so - there was however no gasoline in the delivering system as it surely evaporated durring the winter pause).

[dave92cherokee]

If you put gas in your diesel engine it will not start due to the major fact that diesel engines run on compression alone and have no ignition source. Gasoline requires a spark to ignite the fuel/air mix when it's been compressed to cause the combustion. Diesel combusts from the compression of the piston and uses no spark plugs. Gasoline engines can run on diesel but will produce so much smoke from the exhaust that you will not even be able to see the car.

[silver343124]

Originally Posted by dave92cherokee

If you put gas in your diesel engine it will not start due to the major fact that diesel engines run on compression alone and have no ignition source. Gasoline requires a spark to ignite the fuel/air mix when it's been compressed to cause the combustion. Diesel combusts from the compression of the piston and uses no spark plugs. Gasoline engines can run on diesel but will produce so much smoke from the exhaust that you will not even be able to see the car.

ok I don't know if you are some kind of expert but I do know that you don't know much about engines and surely you don't know thermodynamics equations, according to your statetment.

Gasoline autoignition point is even lower that diesel. For normal gasoline it is 257 deg C for diesel it is 316.

So if the compression temperature ignites diesel it sure will the gasoline!!!!

I think the problem will be as I allready wrote, too high peak pressure and temperature, thus destroying the engine!!!!

[slideways...]

yes. and a couple of companies, notably mercedes benz, are working on a new motor they call the diesotto. compression ignition, gasoline engine with variable valve timing, direct injection, turbocharging, and variable compression. their working prototype has made something like 230hp and 295 lbft from a 1.8 liter 4 cylinder. oh yeah with around 30-40 mpg too.

[silver343124]

Originally Posted by slideways...

yes. and a couple of companies, notably mercedes benz, are working on a new motor they call the diesotto. compression ignition, gasoline engine with variable valve timing, direct injection, turbocharging, and variable compression. their working prototype has made something like 230hp and 295 lbft from a 1.8 liter 4 cylinder. oh yeah with around 30-40 mpg too.

30-40mpg and 230hp! well if that is true, it is some hiiiiiiiiiiiiiighly efficient engine.

with variabile compresion you mean miller cylce wich can be attained with variabile valve lift or hydraulic haead inclination system like found on some saabs?

[Polygon]

Originally Posted by dave92cherokee

If you put gas in your diesel engine it will not start due to the major fact that diesel engines run on compression alone and have no ignition source. Gasoline requires a spark to ignite the fuel/air mix when it's been compressed to cause the combustion. Diesel combusts from the compression of the piston and uses no spark plugs. Gasoline engines can run on diesel but will produce so much smoke from the exhaust that you will not even be able to see the car.

Actually, that's not quite true. If you fill your tank there will be enough fuel in the lines to start the engine. After that runs out the cylinder temps are hot enough to detonate gasoline. That that point the diesel engine blows up.

I know it happened to two diesel trucks that filled up at a station I worked at. The guy put diesel in the 89 tank and 89 in the diesel tank. I made a lot of unhappy customers. A lot of people needed fuel systems flushed while two guys needed engines.

[72chevelleOhio]

It depends on the ratio of the two fuels. I seen a diesel run on a gas mixture, the owner said it had no power, smoked bad and had an extra knock. I accidently put kerosene in my motorcycle. (who expects k1 in a gas container?) I made it about 7 miles then it ran bad and I could feel the extra heat. (air cooled) It died and wouldn't restart, I didn't even make it to the gas station. The bike never did run the same afterwards.

[KiwiBacon]

Originally Posted by Polygon

Actually, that's not quite true. If you fill your tank there will be enough fuel in the lines to start the engine. After that runs out the cylinder temps are hot enough to detonate gasoline. That that point the diesel engine blows up.

I know several people who've had their diesel vehicles filled with petrol. The above did not happen. The engine simply either ran very badly on the diesel/petrol mix in the lines or didn't run at all.

In very cold climates petrol is often mixed in with diesel to prevent the diesel turning into wax.

[curtis73]

Originally Posted by silver343124

30-40mpg and 230hp! well if that is true, it is some hiiiiiiiiiiiiiighly efficient engine.

I have a dually with a cummins diesel making 27 mpg while moving a 7500-lb truck and putting 500 hp to the ground. Its pretty common with the big diesel trucks to get 25+ even with some pretty crazy modifications

[72chevelleOhio]

Originally Posted by curtis73

Its pretty common with the big diesel trucks to get 25+ even with some pretty crazy modifications

Diesel pick-up trucks you mean. 18 wheelers actually only adverage 3 to 7.5 mpg depending on horsepower, how much weight they are pulling, the driver and so on..

[curtis73]

Right. I shouldn't have said "big". I should have said pickup.

[KiwiBacon]

Originally Posted by silver343124

30-40mpg and 230hp! well if that is true, it is some hiiiiiiiiiiiiiighly efficient engine.

Of course you're not getting 30-40mpg while producing 230hp. But you can get 30-40mpg from an engine which can produce 230hp.

Assuming 90km/h
Assume 35 USmpg = roughly 15km/l
Your vehicle would be drinking 6 litres per hour. (5.4kg)
With a BSFC of 200g/kwh that is 27 kilowatts continuous output.

Roughly 36.5 hp.

[slideways...]

Originally Posted by KiwiBacon

Of course you're not getting 30-40mpg while producing 230hp. But you can get 30-40mpg from an engine which can produce 230hp.

exactly. the compression ignition part only happens at certain times to improve efficiency. tnstaafl. oh and i believe the variable compression is like saab's but im not 100% sure. i do know its not miller cycle.

[KiwiBacon]

The only reason I can see for the spark plugs is improved cold-start emissions.

Funnily enough that's how many old tractors and bulldozers used to run, have a valve which opens to reveal a sparkplug and lower the compression. Start on petrol, once the engine is warm switch to diesel and close the valve over the spark plug.

[72chevelleOhio]

Originally Posted by KiwiBacon

Funnily enough that's how many old tractors and bulldozers used to run, have a valve which opens to reveal a sparkplug and lower the compression. Start on petrol, once the engine is warm switch to diesel and close the valve over the spark plug.

I have a 1921 Farmall Regular tractor that starts on gas then you switch it to kerosene when warm. Before you shut it off you switch it back gas and let it run for a little while so it will start next time. It smokes like freight train and used about 11 gallons on a 20 minute run. I don't have it all the way restored yet so it needs tuned in still.