[spkingsley]

Originally Posted by Sutripta

So per litre, a NA diesel should generally have twice the torque (or more, considering diesels normally are long stroke engines) of a petrol?

Regards
Sutripta

Theoretically yes. High reving (4000 rpm) , modern diesels have shorter stroke unlike the earlier low reving truck engines..

[thoma]

Originally Posted by spkingsley

High reving (4000 rpm) , modern diesels

Are you sure that you are comparing apples to apples? Does any modern diesel on the road come without a turbo?

[Sutripta]

Hi,
Continuing what I said earlier, viz

Originally Posted by Sutripta

Considering this thread is more than a year and a half old, I don't think repeating things is going to resolve the issue. So lets try some different tacks.

A) We could compare values from some (apples to apples) engines. ie a NA diesel and a (non screamer) petrol. The American pushrod V8 rumblers come to mind. We would have to normalise/ standardize the results. BMEP, or say Kg-m/ ltr or something like that.

We could start with the Indian example which comes readily to mind: the Indica engine. What could account for the torque values of the petrol and diesel?
http://www.team-bhp.com/forum/techni...ml#post2357828

Let's actually jot down the relevant figures for NA Diesel engines. Considering that modern diesels are turbocharged, NA means the older diesels. But that should suit the 'diesels are torquier' school of thought. Old school diesels were optimised for lugging.

We'll use a calculated metric, torque (Newton metres) per capacity (litre).

Indica 1405 cc 53 bhp 85 N-m 61 Nm/ ltr
Sumo 1948 cc 68 bhp 118 N-m 61 Nm/ ltr
Qualis 2446 cc 74 bhp 151 N-m 62 Nm/ ltr

or lets go to commercial (DI) engines which are optimised for lugging.

T 407 2956 cc 67 bhp 176 N-m 60 Nm/ ltr
T 1210 4788 cc 112 bhp 294 N-m 61 Nm/ ltr

For petrols (choosing common engines) the corresponding figures are

Indica 1405 cc 75 bhp 110 N-m 78 Nm/ ltr
WagonR 1.1 1061 cc 64 bhp 84 N-m 79 Nm/ ltr
Esteem 1298 cc 85 bhp 110 N-m 85 Nm/ ltr
Ritz 1197 cc 84 bhp 113 N-m 94 Nm/ ltr

Normally for NA diesels, we get ~ 60 - 65 Nm / ltr
For petrols, the corresponding figures are ~ 80 - 85 Nm / ltr


These are figures gleaned off the net. If there are any mistakes, pls. correct.

Comments welcome.

Regards
Sutripta

[Aroy]

This analysis is for peak torque. Where the Di/IDI diesels excelled was in low end torque, which is never matched by petrol engines.

[Sutripta]

Originally Posted by Aroy

This analysis is for peak torque.

The last post was not an analysis. It was a compilation of examples to support a point of view. And the underlying theory supporting that point of view has also been stated (a number of times) in the thread.

And I never realised we were discussing only LET. Talk of shifting goalposts! One can ofcourse start a new thread on this new topic.

Where the Di/IDI diesels excelled was in low end torque, which is never matched by petrol engines.

No qualifiers whatsoever!

Regards
Sutripta

[Harbir]

THis might be a worthwhile read, if the content has not already been covered in this thread: http://www.team-bhp.com/forum/techni...ml#post2959278

[suhas.sudhish]

Originally Posted by ahm

This is what I found from Why do diesel engines deliver more torque?
[list=1][*]A gas engine compresses a fuel-air mixture and then ignites it with a spark. A diesel engine ...................transmissions don't come free.

That Solves most of the doubts I had in mind regarding the Stroke differences between a Petrol and a Diesel engine.

[Sutripta]

Originally Posted by Harbir

THis might be a worthwhile read, if the content has not already been covered in this thread: http://www.team-bhp.com/forum/techni...ml#post2959278

Hi,
Thanks for the note on this thread. The diesel torque thing in your top speed thread had escaped my attention.
I take it you mean

Originally Posted by noopster

....
Harbir- can you explain in your trademark "Physics for Dummies" style why diesel engines generate more torque than petrols of the same displacement?
.....

and your answer

Originally Posted by Harbir

There are two parts to the answer to this question. One is relatively straight forward, one is anything but that.
........
So in summary you can thank the higher compression ratio, the low rpm design optimization, and the carnot cycle for the greater torque output of diesel engines.

Because I couldn't find anything else.

Could we begin by listing some torque/ power figures from (NA) diesels (which need HSD). (I have given my examples in a previous post)
Then please go through this thread and list out what you consider wrong information/ assumptions/ extrapolations/ inferences. Must mention that this thread is a result of a merger of two threads, thus making for disjointed reading.

Expecting a lively discussion.

Regards
Sutripta

PS. Diesels use the Carnot cycle?

[Harbir]

I'll go through it when I have some time.

Diesels don't use the theoretically perfect Carnot cycle, but the diesel cycle comes fairly close to the results of the carnot cycle.

[ramzsys]

Originally Posted by Sutripta

Comments welcome.

Regards
Sutripta

I add some examples of NA diesels with peak torque at not so low rpms.

1) Fiat 1.7 59 hp. 100 nm@2900 rpm 82.6 x 79.2 (bore x stroke)
2) ford 1.8 59 hp. 108 nm@2200 rpm 82.5 x 82
3) fiat 1.9 63 hp. 120Nm @2500 rpm 82.0 x 90.4

In the first two engines, i have to rev the engine to get some decent work. Not in the case of the 3rd engine, which can lug its way to any moderate slope.

The same characteristic of the 3rd engine is seen in Suzuki baleno's petrol 1.6 engine with 75 x 90, which people here used to acclaim it as torque moster.

(suzuki 1.6 :96 hp, 135nm @3000 rpm).

Thus from this naive approach, i conclude that it is not the fuel but the engine construction that gives torque.

[SPIKE ARRESTOR]

Originally Posted by Sutripta

We'll use a calculated metric, torque (Newton metres) per capacity (litre).

Indica 1405 cc 53 bhp 85 N-m 61 Nm/ ltr
Sumo 1948 cc 68 bhp 118 N-m 61 Nm/ ltr
Qualis 2446 cc 74 bhp 151 N-m 62 Nm/ ltr

or lets go to commercial (DI) engines which are optimised for lugging.

T 407 2956 cc 67 bhp 176 N-m 60 Nm/ ltr
T 1210 4788 cc 112 bhp 294 N-m 61 Nm/ ltr

For petrols (choosing common engines) the corresponding figures are

Indica 1405 cc 75 bhp 110 N-m 78 Nm/ ltr
WagonR 1.1 1061 cc 64 bhp 84 N-m 79 Nm/ ltr
Esteem 1298 cc 85 bhp 110 N-m 85 Nm/ ltr
Ritz 1197 cc 84 bhp 113 N-m 94 Nm/ ltr

Normally for NA diesels, we get ~ 60 - 65 Nm / ltr
For petrols, the corresponding figures are ~ 80 - 85 Nm / ltr

I think these figures are a pretty good hint to start with. Why do diesels and petrols follow this range?

Originally Posted by Sutripta

PS. Diesels use the Carnot cycle?

Originally Posted by Harbir

Diesels don't use the theoretically perfect Carnot cycle, but the diesel cycle comes fairly close to the results of the carnot cycle.

How close, if yes why? IIRC, diesel cycle is assumed as a constant pressure cycle right?

A question comes to my mind, why prefer the Seiliger cycle then?

Spike

[Sutripta]

Hi,
Ramzsys, I'm going to plagiarize your data, and add the 'specific torque' figures. That gives

Diesels
1) Fiat 1.7 59 hp. 100 nm@2900 rpm 82.6 x 79.2 58 Nm/ Ltr
2) Ford 1.8 59 hp. 108 nm@2200 rpm 82.5 x 82 60 Nm/ Ltr
3) Fiat 1.9 63 hp. 120Nm @2500 rpm 82.0 x 90.4 63 Nm/ Ltr

Suzuki Baleno Petrol
1.6 :96 hp, 135nm @3000 rpm 84 Nm/ Ltr

Thanks a lot.

Originally Posted by SPIKE ARRESTOR

I think these figures are a pretty good hint to start with. Why do diesels and petrols follow this range?

Good to see you on this thread. Your insights will be appreciated.
Do you have figures for GDIs?
What is the current status for HCCIs?

Regards
Sutripta

[SPIKE ARRESTOR]

Originally Posted by Sutripta

Good to see you on this thread. Your insights will be appreciated.

I am trying to figure out air standard cycles, confused after reading posts here.

Do you have figures for GDIs?

No.

What is the current status for HCCIs?

No idea.

Spike

[SS-Traveller]

Originally Posted by Sutripta

...torque is a function of how much air is used for combustion. As I have mentioned before, the increased compression of a diesel is not enough to compensate for the fact that a diesel is unable to use all its air.
Examples of diesels with high max torque/ litre. (NA engines for proper comparison)

Came in and joined the party a little late, I see...

Why the sudden silence after a brilliant round of discussions?

Now that it is QED that NA petrols produce more torque than NA diesels, what happens to torque figures for diesels and petrols of similar displacement where both are turbo-charged (or, well, even super-charged)?

[Sutripta]

Originally Posted by SS-Traveller

Now that it is QED that NA petrols produce more torque than NA diesels,

QED? I very much doubt it.
Everyone knows diesels produce more torque than petrols. A couple of posts stating otherwise, in a fun (ie non professional) forum is not going to convince anyone. All it will result in is everyone googling away for rebuttals.

what happens to torque figures for diesels and petrols of similar displacement where both are turbo-charged (or, well, even super-charged)?

Waiting for the more learned members to educate us.

Regards
Sutripta