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Old 3rd May 2013, 23:01   #196
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Default Re: Do Diesel engines generate more Torque than Petrol engines?

^^ Ah, I remember those posts from Sutripta, thanks for the reminder, the first part is clear. Now the next question, looking for convincing answers, why so ?

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Old 3rd May 2013, 23:47   #197
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Default Re: Do Diesel engines generate more Torque than Petrol engines?

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Originally Posted by FlatOut View Post
A petrol engine will produce more power because it can rev faster.
I think your statement is technically wrong. At-least partially.

First of all producing more power has nothing to do with "revv faster" which is BTW a vague term. It should have been revv higher.

* Petrol engine rev faster because they have shorter gear ratios to compensate for lower torque & higher revv range. It has got nothing to do with power but gear ratios.
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Old 4th May 2013, 00:26   #198
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Default Re: Do Diesel engines generate more Torque than Petrol engines?

What does petrol engine revving faster got to with the gear ratio?

If both the engines have the same Cubic Capacity and bore ,the Diesel engine will still requires longer strokes then a similar sized petrol engine hence they can't rev as fast as a petrol engine which isn't going to compress the fuel as much diesel.So since the stroke of the petrol is smaller ,i assume that the petrol engine can rev faster then a diesel engine ,even if one limits the petrol engine max RPM to that of the diesel engine.

Last edited by aim120 : 4th May 2013 at 00:27.
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Old 4th May 2013, 00:59   #199
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Default Re: Do Diesel engines generate more Torque than Petrol engines?

Guys, here is some info about the piston velocities of the two types -

Diesel - max ~ 15 m/s, and that too for TC Diesels
Gasoline - goes up to max ~ 25 m/s, NA Gasoline.

For race car types, I guess these are much higher. Keeping the gearing aside, is it only the nature of combustion between the two or something else which plays a role? If I keep the bore and stroke same (square, undersquare or oversquare for both of these) , what happens then?

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Old 4th May 2013, 02:54   #200
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Default Re: Do Diesel engines generate more Torque than Petrol engines?

Quote:
Originally Posted by oxyzen View Post
I think your statement is technically wrong. At-least partially.

First of all producing more power has nothing to do with "revv faster" which is BTW a vague term. It should have been revv higher.

* Petrol engine rev faster because they have shorter gear ratios to compensate for lower torque & higher revv range. It has got nothing to do with power but gear ratios.
Of course 'revv higher' is far less vague. Although I see you then use it yourself, having denigrated it!

The engine revs faster (more quickly/at greater speed/more rapidly) but the number go higher.

Since power is the rate at which work is done. the more quickly you do this work then the more power is generated. Torque and power are difficult concepts and closely related, but an engine (non IC) can generate massive torque from zero revs whereas the power is related to the ability to turn.

Another way of thinking of it is that an engine which has a lot more torque than power will feel un-stallable and be very easy in stop-start conditions and good at pulling heavy loads and climbing hills without apearing to need to be worked hard.
Conversely, the opposite situation will be an engine which feels nervy and very willing to rev, but which is easy to stall and suddenly appears to have lost all its urge if asked to pull a load and work hard.

French engines traditionally have a lot of torque low down (which enhances the driveability of a car through twisting roads - many French petrol engines are almost as driveable as a good diesel) whereas the Germans (who have had unlimited speed motorways since the 1930s) have always tuned for torque higher up, since as speeds rise, the need for more ability to overcome the rapidly rising air resistance is the most important need from their perspective. A French car in Germany can feel legless, a hugely powerful German car in France will soon lose ground to a much less powerful French car.
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Old 11th May 2013, 17:54   #201
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Default Re: Do Diesel engines generate more Torque than Petrol engines?

Dear SPIKE

where did you get this information? Can you point at the source?

Also (if you know) what are the limiting factors for diesel and petrol piston velocities?
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Old 11th May 2013, 18:05   #202
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Default Re: Do Diesel engines generate more Torque than Petrol engines?

Vina, I think these values are from my lecture scripts. I remember reading about piston velocities somewhere in Heywood too.

The limiting factor I know off are -

a) Combustion (in general), specially for Diesel engines
b) Stress due to peak mean effective pressures etc.

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Old 1st June 2013, 18:30   #203
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Default Re: Do Diesel engines generate more Torque than Petrol engines?

Quote:
Originally Posted by SPIKE ARRESTOR View Post
Vina, I think these values are from my lecture scripts. I remember reading about piston velocities somewhere in Heywood too.

The limiting factor I know off are -

a) Combustion (in general), specially for Diesel engines
b) Stress due to peak mean effective pressures etc.

Spike

Heywood just mentions the peak piston velocity without telling where it comes from.
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Old 1st June 2013, 19:17   #204
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Default Re: Do Diesel engines generate more Torque than Petrol engines?

^^ Yes, I think so, do you think these values are not correct?

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Old 1st June 2013, 21:11   #205
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Default Re: Do Diesel engines generate more Torque than Petrol engines?

Here is an article of diesel engine design. It has amongst others various parameters we have been discusiing
http://www.fev.com/fileadmin/fev-res...dieselcomp.pdf

. Now diesel engines are being developed for the Aviation industry
http://www.deltahawkengines.com/aboutdeltahawk.shtml
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Old 1st June 2013, 21:15   #206
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Default Re: Do Diesel engines generate more Torque than Petrol engines?

Way back in school I learnt oil burners provide more torque than gasoline engines.
Later on, we ( as in a few automotive nutty friends) used to debate over all this, our conclusion was, Oil burners had more lugging power and was basically truck/train fuel. While a petrol engine has a wider powerband Diesels had a narrow powerband. Ofcourse the common rail changed all that. Still remember reading about it in an automag during the early 90z.

Most trucks are diesel. Diesel is cheaper that petrol in India. Its not the case in many countries.

Why?( the torque bit, not the price.. that we all know! ) I do not know. But I think its a yes.

OT: among other topics related to cars/bikes one was about LED tail lamps/ and other automotive lights. A friend predicted most cars would have LED lamps sometime. He is with IAF now.

Last edited by YaeJay : 1st June 2013 at 21:19.
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Old 1st June 2013, 22:22   #207
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Default Re: Do Diesel engines generate more Torque than Petrol engines?

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Originally Posted by YaeJay View Post
...
Most trucks are diesel. Diesel is cheaper that petrol in India. Its not the case in many countries.

Why?( the torque bit, not the price.. that we all know! ) I do not know. But I think its a yes.
The low end torque of diesel engines makes them perfect for heavy haulage. The narrow power band is not much of a problems and most of the trucks have 10 or more gears so that you are always in the optimum power band.

Another advantage of diesels is their FE, which can be as much as 50% more, which makes even more economic sense to have a diesel. Add to that tougher construction which results in engines clocking a millions of kilometers easily. This makes diesels the darling of transportation operators.

The only sector which is moving away from diesels to petrol are vehicles designed for regular use in extreme low temperature : -40 degrees or less.
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Old 1st June 2013, 23:19   #208
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Default Re: Do Diesel engines generate more Torque than Petrol engines?

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Originally Posted by YaeJay View Post
Oil burners had more lugging power and was basically truck/train fuel.
While many would know it, but diesel in train is not directly used for 'pulling'. The diesel is used as fuel for running a powerful generator which actually powers electric motors, which actually makes the train move. Its tough for diesel or for that matter any fuel to haul a load as much as of a train.
Sorry for the OT.

Regards,
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Old 2nd June 2013, 08:49   #209
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Default Re: Do Diesel engines generate more Torque than Petrol engines?

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Originally Posted by saket77 View Post
While many would know it, but diesel in train is not directly used for 'pulling'. The diesel is used as fuel for running a powerful generator which actually powers electric motors, which actually makes the train move.

Regards,
Saket
Correct! Technically its correct name is diesel/electric. Without the electric bit a diesel train would need gears, just like a car/truck. Interestingly, another anorak OT fact, there have been trains with gears. Mostly light passenger trains.

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Old 2nd June 2013, 18:43   #210
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Default Re: Do Diesel engines generate more Torque than Petrol engines?

Quote:
Originally Posted by saket77 View Post
While many would know it, but diesel in train is not directly used for 'pulling'. The diesel is used as fuel for running a powerful generator which actually powers electric motors, which actually makes the train move. Its tough for diesel or for that matter any fuel to haul a load as much as of a train.
Sorry for the OT.

Regards,
Saket

Yes correct. The reason I heard was because they can't have a clutch to take all that torgue. So they have only electric motors at the wheels.
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