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-   -   What is the benefit of using low rpm diesel engines? (https://www.team-bhp.com/forum/technical-stuff/125688-what-benefit-using-low-rpm-diesel-engines.html)

Chevrolet Optra Magnum has 2 L diesel engine which gives maximum power of 89KW@3000 rpm

Sumo Gold (CR4) 3.0 L diesel engine gives 62KW@3000 rpm

Toyota Dyna (Singapore) 3.0 L diesel engine gives 80KW@3000 rpm

Toyota Hiace (Bhutan) 3.0 L diesel engine gives 80KW@3000 rpm

Where as most of the other auto diesel engines give maximum power at somewhere between 3600 to 4400 rpm .

May I know what is the advantage of using diesel engines which gives maximum power at low rpm like 3000 or likewise.

This will answer your question
HowStuffWorks "Why do big diesel engines and race car engines have such different horsepower ratings?"

Due to the nature of combustion, and high compression you have
1. Longer stroke
2. Heavier components.

So a lower RPM makes more sense practically

May I know why have you written the figure in Kilowatts? We always have car engine ratings in PS/DIN (Metric) or HP (Imperial) right. This it the first time I'm seeing someone convert to an electrical generating Unit.
Which are the engines you refer to as diesel engines give maximum power at somewhere between 3600 to 4400 rpm ?
Diesel engine speed is controlled why a governor for idling and top speed, if it runs any faster that it was designed to it will kinda destruct.

OK sir, I can give you examples of so many diesel engines where the maximum power is at higher rpm. For example
(1) Indica V2 diesel......52.5 PS @ 5500 rpm
(2) Indica EV2 diesel....70 ps@ 4000 rpm
(3)Toyota d4d for Corolla 88ps@ 3800 rpm

Is that OK ?
As for the use of unit KW instead of bhp or PS , it is a CGS system which has universal acceptance.Even in technical brochure of Indian cars the KW unit is considered. Hope this explaination is OK for u.

Thanks for the info. Aren't the engines of the two indica models the same except that the second one has a turbo with an intercooler. Regards

+1.

Diesel requires a different combustion method, and the overall process, set-up result in power being delivered at lower RPM. This also makes diesels more suitable for heavier loads than for higher speeds - as compared to Petrol.

I think the OP's question was more as to why few diesels have power lower in the rev band than some other one's.

I don't know the perfect answer but what i think is: The engines are not designed or tuned with power in mind per se. They are always designed with the torque requirements. When this is done the power is later calculated.

Ex: Formula one engine needs very high power. Solution-Design the engine to produce peak torque at highest rpm.

P=[2(pie)nT]/60. Also, T(Nm)=[9550*P(kw)]/n(rpm)
n-rpms, T-torque, P-power

In essence, Power - Torque/Time or Power - Torque * RPM
So when an engine is designed to provide maximum torque high up the rev range it will automatically have a big power rating. But it will have horrible power delivery low down the rev range (lack of torque). Simple proof - F1 car 0-100 2.6s; 100-200 22.5s; An f1 car does 100-200 faster than its own 0-100. This is because it gives out most of its torque higher up the rev range!

Therefore, for large SUVs and MUVs the engines are designed to provide large torque very low down in their rev range so as to aid load lugging capacity or off roading capacity (very low speed lugging). Hence they give their maximum power will be less and delivered a bit lower down the rev range.

If your question was why diesels have lower power or at lower rpm when compared to petrols the the above post have answered your question!!

Hope this helps!!

1 hp is 746 watts approx 0.75kW. As for PS and bhp they are the same within 3%.

Yes sir , this is exactly the point I was expecting. This engine set up is to provide large torque at low rpm range to aid load lugging capacity in case of Dyna 3.0 100 model (singapore) and Hiace Van (Bhutan) and to aid off road capacity in case of Sumo Gold(CR4). In such tune up the maximum power at low rpm (say 3000 rpm) is moderate compared to different tune up of the same engine where maximum power could be at 3600 to 4000 rpm. Also such set up could be fuel effecient. In countries like Bhutan or India ( particularly south Himalaya type hilly region or rural region without proper road network) it makes more sense to opt for design for moderate power and large torque and yet getting good fuel efficiency.

Related threads :

1) What the difference between a Diesel and Petrol engine??

2) Do Diesel engines generate more Torque than Petrol engines?

3) Power characteristics of long and short stroke engines?

4) Oversquare diesels

cya
R

Without any help (turbocharging etc), the torque of a DI diesel is mainly dependent on the displacement. That is higher the displacement more the torque.

To get more displacement (hence torque) without increasing the piston diameter, you use a longer stroke. Once the stroke is long, its top speed will be limited. So if you are interested in moving heavy load at a reasonable speed a long stroke engine will be the answer.

Most of the DI engines have a hefty torque at LOW RPM and it peaks quite fast and tapers off faster. The advantage is that if you need more load carrying capacity rather than speed, a lower speed higher torque engine is preferred. Another advantage of a lower speed engine is that it wears out much less.

With CRDI technology, and shorter stroke engines, the designers were able to push the RPM quite a lot. Add a turbo and the limit is raised further.

As power is torque x RPM x constant, the higher RPM engines not only deliver more power but at a higher RPM, enabling vehicles to travel faster. The catch is that as these engines have smaller displacement for same peak power, they suffer from lower "Low End" torque (also called lugging power).

Now come to the benefits of lower speed non CRDI engines -

. Better low end torque, hence better performance in "sticky" situations, especially at RPM where the turbo is ineffective (hence off).

. Longer engine life - the combination of lower operating speed combined with sturdier construction.

. Can be designed with no electronics, hence higher reliability, useful in remote areas - expeditions.

. Can use inferior fuel.

That is why most of the manufacturers who are in the 4x4 expedition vehicles (and army supply) have an option for a low speed non CRDI engine along with a CRDI engine. Landcruiser series 70 comes to my mind.

Sorry, raking up an old thread.
I have a 1.5 TDCi EcoSport 2019 model. Do I need to drive the vehicle in turbo zone (1500-2000 rpms) continuously to squeeze out the best fuel economy? I doubt it because lot of forums talk about the fact the more revs climb, the less fuel economy will you get. Does that mean driving in 1000-1200 rpms range, and upshift ASAP ? I doubt it again, as this will leave unburnt fuel stuck to the exhaust and may cause long term engine wear and tear. Really confused, please enlighten me (coming from NA petrol engine).

It is true that fuel consumption increases with increase in engine RPM. But do not upshift early and keep driving at 1200rpms. You wont save much fuel and would ruin the engine. The 1.5TDCi has peak torque from 1700rpm, so upshift keeping in mind that you stay around 1700 rpm after upshifting. So around 2K will be a good spot. (in flat roads). If you upshift too early, you will actually burn more fuel to produce enough exhaust gas to drive the turbo.

Having said that, it is better to the listen to the engine and upshift. It is easy to figure out the optimum shift points by observing the engine note and the way it responds to throttle input.

Thanks sir. Yes, upshift too early it's not good for engine. I will try sticking to the sweet spot then- 1500-2000 rpms. But then, I also observed that the engine really pulls cleanly only during the 1000-1500 rpms range, and also at this stage nvh is not at all intrusive. Hit the rpms beyond 1500 rpms, nvh and pulling becomes a suspect. Thoughts?

The NVH would increase as it is a diesel and it is normal but if it does not accelerate well after 1500, it is better to get the car checked. As a matter of fact, the engine should accelerate better after 1500 as it would have maximum boost beyond that RPM. If you have been driving all this while at low rpms, then it would take a while for the ECU to adapt to the new driving style.

To keep the engine soot free, after the engine has reached operating temp., drive at high rpm for a few minutes (~10-15mins) in an open stretch of road.
(Read about italian tune ups:thumbs up)

PS : I'm way too young to be a 'Sir':D