[Thad E Ginathom]

Originally Posted by anupmathur

Tekno, once the underlying principles are grasped, there is no difference in driving a petrol or diesel vehicle. This is not a game of absolute numbers but of trying to listen to what the engine is saying! Engines talk, yes!

Absolutely right. The diesel has greater tolerance, but the principles and basic practice are the same.

[Atlblkz06]

Originally Posted by pLeaSe Dont

Imo universal speeds to respective gear shifts should be as follows
0-5 kph -1st gear
5-20 kph-2nd gear
20-30 kph-3rd gear
30-40 kph-4th gear
40 kph- 5th gear

NOPE! I made the mistake of posting vague numbers on an earlier post and got killed for it.

My Vette hits 100km in FIRST gear. There goes your universal theory out the window.

[revtech]

Originally Posted by Atlblkz06

My Vette hits 100km in FIRST gear. There goes your universal theory out the window.

thats when your redlining it.not during optimum (read fuel economy) gear shifts.those speeds are to get a decent fuel economy without lugging the engine.

rev

[Atlblkz06]

Originally Posted by revtech

thats when your redlining it.not during optimum (read fuel economy) gear shifts.those speeds are to get a decent fuel economy without lugging the engine.

rev

If I want optimum, I'll drive a hybrid. Between 15mpg + boring and 12mpg+ fun, I choose the later. I sounds like our buddy GTO now don't I?

[Crazy_Eddy]

Do diesel engines knock/ping ?

[SS-Traveller]

Originally Posted by Crazy_Eddy

Do diesel engines knock/ping ?

Of course they do... If they didn't, most of us would be driving around in 5th gear at 20km/h.

Tekno, once the underlying principles are grasped, there is no difference in driving a petrol or diesel vehicle. This is not a game of absolute numbers but of trying to listen to what the engine is saying! Engines talk, yes!

[anupmathur]

Originally Posted by Crazy_Eddy

Do diesel engines knock/ping ?

Yes they do.
Octane number for petrol, cetane number for diesel.

If the octane or cetane number is too low for the compression ratio of the engine, pinging takes place.

[teknophobia]

Originally Posted by anupmathur

Yes they do.
Octane number for petrol, cetane number for diesel.

If the octane or cetane number is too low for the compression ratio of the engine, pinging takes place.

Diesel engines work on the same principle that causes "knock" in petrol engines. Unlike petrol engines, where the fuel is injected before the compression cycle, in diesels, fuel is injected just before the end of the compression cycle, consequently, there is no fuel in the cylinder to catch fire before the intended time and cause "knock".

A higher cetane number indicates the capacity of the diesel to catch fire quickly whereas octane number indicates the capacity of the petrol to avoid spontaneous ignition.

Similar to the octane number rating that is applied to gasoline to rate its ignition stability, cetane number is the rating assigned to diesel fuel to rate its combustion quality. While gasoline's octane number signifies its ability to resist auto-ignition (also referred to as pre-ignition, knocking, pinging, or detonation), diesel's cetane number is a measure of the fuel's delay of ignition time (the amount of time between the injection of fuel into the combustion chamber and the actual start of combustion of the fuel charge).

Because diesels rely on compression ignition (no spark), the fuel must be able to auto-ignite--and generally, the quicker the better. A higher cetane number means a shorter ignition delay time and more complete combustion of the fuel charge in the combustion chamber. This, of course, translates into a smoother running, better performing engine with more power and fewer harmful emissions.

Source: Diesel Cetane Number - Diesel Fuel Cetane Rating - What is Cetane

There's a very good reason why I suggested that there be separate threads for petrol and diesel engines, they work on completely different principles and have completely different characteristics. I observe that there are a lot of misconceptions about diesel engines here, even among senior forum members. To appreciate the diesels, you need a complete change in how you think and how you drive.

[anupmathur]

Originally Posted by teknophobia

Diesel engines work on the same principle that causes "knock" in petrol engines.
.....

Tekno, please take a look at this: Diesel engine combustion efficiency

and: Knocking detection device in diesel engine - Patent 4567751

And: Automotive: knocking in diesel engine, vw golf diesel, vw dealer

[architect]

Ok, let me ask (for the umpteenth time) again.

I have a Palio Multijet. I drive at idling RPM on 1,2,3 gear (not 4th / 5th) in crawling traffic and I manage without any protests whatsoever from the engine. It is also a welcome respite from manipulating the heavy clutch.

That is not lugging.

Now, I need to speed up. When i depress the A-pedal, the engine tends to become jerky, so it has to be done very gently. On 1st & 2nd gear, this pick-up is somewhat smoother than on the 3rd. I haven't tried on 4th but, I assume, it will chug along easily on idle, but will require more gentleness on pick-up.

This 'jerkiness' or 'un-willingness' to accelerate is lugging.

Am I correct?

P.S. I have also noticed that the ECU increases the RPM marginally (100 RPM from 600 to 700) from idle on it's own when I am chugging along at idle RPM. It also does that if I hit a slight incline. Which means I can start moving forward up a slope without pressing the A-pedal on 1st gear from rest my releasing clutch. Is that advisable?

[vineethvazhayil]

Originally Posted by Shan2nu

There is no specific rpm for lugging.

A car doing 1500rpm in 3rd going uphill with full load will obviously come under a lot of stress compared to the same car doing 1500rpm in 3rd going downhill (or even on a flat surface) without any passengers.

So instead of sticking to fixed rpm figures, improvise your gear shifts wrt diff load conditions.

Shan2nu

Correct! It would be hard to define lugging rpms. You should be judging from the engine sound and feel. But then how many people bother to do that, I really don't know.

[supremeBaleno]

Originally Posted by architect

I have a Palio Multijet. I drive at idling RPM on 1,2,3 gear (not 4th / 5th) in crawling traffic and I manage without any protests whatsoever from the engine. That is not lugging.

Yes, as long as the engine sounds fine and is not strained, you are not lugging.

Originally Posted by architect

Now, I need to speed up. When i depress the A-pedal, the engine tends to become jerky, so it has to be done very gently. On 1st & 2nd gear, this pick-up is somewhat smoother than on the 3rd. This 'jerkiness' or 'un-willingness' to accelerate is lugging. Am I correct?

Again, you are right - this qualifies for lugging because the engine sounds un-willing / jerky when you try to accelerate quickly. BTW,

Originally Posted by architect

I haven't tried on 4th but, I assume, it will chug along easily on idle, but will require more gentleness on pick-up.

Actually instead of 'more gentleness, it would be better to downshift to 3rd or whatever is the suitable gear for that speed/rpm and pick-up from there.

Originally Posted by architect

Which means I can start moving forward up a slope without pressing the A-pedal on 1st gear from rest my releasing clutch. Is that advisable?

From what you mentioned, I don't see anything wrong with this.

[Samir Taheer]

When the ECU increases the RPM, is this not the Anti-stall kicking in? The ECU will only allow the Anti-Stall to kick in upto a certian extent. Moving up the slope without any acceleration, would be putting strain on the engine? So it cant be good for the car. Yes?

On the same basis - If you driving along at Idle and the ECU is varying the RPM, is it not putting in the required fuel to stop the car from stalling? Are you then actually getting extra millage?

[anupmathur]

Originally Posted by Samir Taheer

When the ECU increases the RPM, is this not the Anti-stall kicking in? The ECU will only allow the Anti-Stall to kick in upto a certian extent. Moving up the slope without any acceleration, would be putting strain on the engine? So it cant be good for the car. Yes?

I'd say it can't be good for the car/engine. And it certainly is not the ideal point of operation.

[supremeBaleno]

Originally Posted by Samir Taheer

Moving up the slope without any acceleration, would be putting strain on the engine? So it cant be good for the car. Yes?

You do have a point. But again I would think that this depends on the engine capability. If your car engine produces enough torque at really low rpms that enable the car to climb up gradients without straining the engine, I would think it OK. But if you try the same thing on another lower-specced car, it might strain the engine, in which case, its would be a no-no.