Dipping my toe in the Eco-modder world

[jmcc]

Hi,

Quick intro. My name is James, I am an automotive engineer specialising in Diesel engine calibration development. I work for an engineering consultancy in the UK and my work has been on projects including hybrid demonstrators, low emissions diesels, production calibration development, control strategy specification and development and even low cost Indian engine development.

I was interested to see these forums from a professional perspective, I don't drive enough miles to get into modding my own vehicles.

If anyone has questions on modern diesel engines I may be able to help. I know nothing on aero though!

Cheers,

James

[Tesla]

Welcome,
Great to have you on board.
I'll open up with some questions.
My priorities in order are reliability, economy, performance.
My vehicle is powered by a turbo diesel engine (ZD30 Di), I have done a lot of trials playing with the Variable nozzle control on the turbo, have tried manual controls, but am currently running with ECU control.
My most recent mod was improving air supply to turbo by accessing the pressure at the front of the vehicle, like a ram air setup, response, power & economy all improved. On that mod my assumption is if I can increase pressure to the turbo, then that will reduce exhaust pressure drop across turbo, hence improving exhaust flow and reducing pumping losses.

The first question is, under load increased pressure to turbo is good, but when coasting down, no load, will the engine run more freely if I also restrict the intake, noting I already open the VNT fully to allow a more free exhaust flowundere this condition?

The other thing that I am exploring is whether running at lower boost will give better economy figures, provided the EGT's stay in an acceptable range, is this the right direction?

And in general, any pointers for achieving the best economy from a modern diesel engine?

[MetroMPG]

Welcome to the forum, James. Glad to see another professional in the field interested in the subject matter here.

[jmcc]

Originally Posted by Tesla

The first question is, under load increased pressure to turbo is good, but when coasting down, no load, will the engine run more freely if I also restrict the intake, noting I already open the VNT fully to allow a more free exhaust flowundere this condition?

A colleague of mine worked on that engine extensively during development. Interesting question. I think you actually want to supply pressure, or at least not a depression, during overrun as restricting the airflow will only increase pumping work. We sometimes apply an intake throttle to increase engine braking which I guess is the effect you're trying to avoid.

Originally Posted by Tesla

The other thing that I am exploring is whether running at lower boost will give better economy figures, provided the EGT's stay in an acceptable range, is this the right direction?

I would have to look at some data, but generally the base cal wouldn't be demanding (or achieving) too much boost at most conditions. You really need to keep the AFR up as combustion efficiency will worsen as you go richer, certainly when you get down below 25:1 or so. For reference, you'll be getting visible smoke (if no DPF) below about 22:1.

Originally Posted by Tesla

And in general, any pointers for achieving the best economy from a modern diesel engine?

I'd focus on keeping max revs below 1800-2000 rev/min as a starter. I'll dig out some typical BSFC maps if of interest so you can see where to run.

James

[jmcc]

Oh, and if you can disable EGR without tripping a MIL then that's worth a couple of mpg straight out (to the detriment of NOx, but hey ho).

[ecomodded]

I am hoping with your back ground that you can shed some light on my musings on airflow and the vw tdi diesel.

I am thinking that a restriction in the intake airflow would cause the motor to use less gas. As the mass air-flow senor on the intake tube would be reading less airflow, and ask for the appropriate amount of fuel to mix with the restricted airflow, Causing less fuel to be burned when demanded by the throttle. a hp restrictor of sorts.
What are your thoughts on this actually increasing or decreasing fuel economy ?

[jmcc]

I haven't worked with a VW TDI, but I don't think that will work. Diesel engines deliver fuel according to the driver request via the gas pedal, and unlike gasoline (petrol) engines they do not adjust fuel to match an AFR other than at full load where there will be a fuel limitation based on available air (to avoid going too rich and generating smoke). What a diesel engine does is to control airflow to ensure there is sufficient for the fuel delivery. I suppose ultimately that restricting air would put you on the smoke limited AFR level sooner, but you would always be pumping against that restriction so the net effect would be negative.

I'd suggest your best option would be to put a false throttled stop on your pedal to stop you going to high load and hence avoid high fuel delivery!

[Tesla]

Thanks for the responses James,
Just the sort of info I've been trying to get

Originally Posted by jmcc

A colleague of mine worked on that engine extensively during development. Interesting question. I think you actually want to supply pressure, or at least not a depression, during overrun as restricting the airflow will only increase pumping work. We sometimes apply an intake throttle to increase engine braking which I guess is the effect you're trying to avoid.

With the overrun/coasting, I was thinking that there may be a minimum pumping losses point where the suction (under mild restriction) required on the intake stroke was balanced by the forces required in the compression and exhaust strokes, knowing ofcourse that the exhaust system itself has ideal flow requirements to help draw the exhaust out of the engine.

Originally Posted by jmcc

I would have to look at some data, but generally the base cal wouldn't be demanding (or achieving) too much boost at most conditions. You really need to keep the AFR up as combustion efficiency will worsen as you go richer, certainly when you get down below 25:1 or so. For reference, you'll be getting visible smoke (if no DPF) below about 22:1.

Running with the VNT fully open, which is effectively then a Turbo sized for High rpm on the ZD30 engine, around town it is virtually no boost, but seems like torque & power curves drop to a lower rpm range, and also drop in an absolute sense. On the highway at 100-110km/hr 2,500 to 3,000 rpm it achieves 3-5psi, I do not see any visible smoke, my gut feeling is that the ideal spot for fuel efficiency is somewhere between the ECU settings and the fully open VNT. I did notice an increase in EGT's with VNT fully open, but that's another question of the EGT drop across the turbo, my pyro is mounted post turbo and I hear the drop in temp is variable and dependant on Boost pressure, rpm, load etc. eg at idle may be no temp drop, but at high boost & load could be 200-250C.

Originally Posted by jmcc

I'd focus on keeping max revs below 1800-2000 rev/min as a starter. I'll dig out some typical BSFC maps if of interest so you can see where to run.

James

Definately interested if you can dig up some relevant BSFC maps, still reading up and getting my head around the whole BSFC story.
I will give that a try, with this engine max torque is around 2,000rpm and I find it is quite comfortable to drive around that rpm, except at higher loads when it really cranks up at the 2,500 - 3,500 range.

Originally Posted by jmcc

Oh, and if you can disable EGR without tripping a MIL then that's worth a couple of mpg straight out (to the detriment of NOx, but hey ho).

Have been toying with that one for a while, i know it is better for the engine in terms of longevity, but wanted to get a better idea re economy. Is this generally true for all diesels, or all engines for that matter? I surmised that there may possibly be a reduction in pumping losses, by pushing exhaust from one cylinder directly into the intake on another, like a bit of a balanced closed loop idea, but your opinion tends to sway me more towards the negative effects of the EGR system.

Thanks again James,
great information and sorry for picking your brain with a jackhammer, just been starved for info on this particular topic.

[SoobieOut]

Welcome James

I have often wondered why no one has tried to produce a scaled down version of a high performance diesel engine like the Audi R10 TDI. Using only 2 or 3 cylinders and high boost pressure. This would reduce size and weight of the engine. I think high fuel economy could be attained.

[jmcc]

Originally Posted by MorphDaCivic

Welcome James

I have often wondered why no one has tried to produce a scaled down version of a high performance diesel engine like the Audi R10 TDI. Using only 2 or 3 cylinders and high boost pressure. This would reduce size and weight of the engine. I think high fuel economy could be attained.

I think the issue is basically getting the air system to work. Turbos don't really scale easily, so for a small capacity engine to run high boost pressures you need an over-sized turbo. This means transient response will be poor. To overcome this you need a twin turbo system, a small one for low speeds, and a big one for high speeds/loads. This is why BMW fit 2 turbos which to the 123d and 535d, and 3 to the 550d! And they're not even small capacity engines.

One interesting tech is the CPT electric supercharger which can be used to fill in the low end torque, allowing a large turbo for high load. Needs more control and calibration effort, but has been demonstrated a few times.