7 replies to this topic

[GSX-R]

Hello,

I think to know that A/F ratio on diesel is beetween 1:18 and 1:50-60.

What i would like to know is how the turbo diesel engines ECUs are programmed to provide a torque according to the load around mid revs.

They can adjust boost pressure (if they have a wastegate valve or a electric variable nozzle on the turbo) AND/OR the Air/Fuel ratio. What is commonly the A/F targeted at mid-load@mid-rev ?

I try to guess the A/F ratio on some cars from the boost pressure like bmw 330d and even Renault Laguna dci 2.0 175cv (both around 21 bars BMEP) and i find values around 1:25. So if i'm right the A/F ratio could be reduced around 1:18 but like with a lot turbod engines, the torque is limited not to get a too much Pmax value or exhaust gaz temperature for the turbo. So why to boost so much and not to reduce the A/F ratio ? Do the turbo really reach the documentation value at max torque RPM ? Just to run cleaner, to reduce the exhaust temperature ?

Do the engine run near the 1:18 when on margins or out of the turbo range ?

Last, do the modern engines featuring electronic controlled VNozzle turbo discharge often ?

Regards

GS

[J. Edlund]

The position of the pedal is translated into a torque demand, this demand is then used to calculate the amount of fuel added per combustion. Boost pressure is not used to control torque, instead the boost pressure is calculated from a map based on rpm and fuel added, this value is then corrected by the atmospheric pressure.

To keep emissions of particles (soot), CO and HC low the diesel engine must always operate with excess air, the exact number may differ but is in the region of 30%. In general both emissions and fuel consumption benefit of running with leaner mixtures.

Thermal and mechanical limits of the engine also put limits on the amount of fuel that can be injected and the timing of the injection.

Since there is no lambda sensor on a diesel, so instead fuel and air flow is used.

[NTSOS]

I wonder why the implementation of traction control seems to be such a big deal as it relates to the R10?

John

[GSX-R]

Originally posted by J. Edlund
The position of the pedal is translated into a torque demand, this demand is then used to calculate ...

Do you mean that boost pressure on modern turbo diesel is rarely (never ?) controlled by the ECU ?The turbo would be only regulated for a max rpm limit OR boost pressure ?

The reason why we ear the turbo in action when we press the pedal is just because we burn more fuel and so exhaust pressure run the turbo (no wastegate control until boost pressure/turbo rpm ) ?

The goal would also be to run with the more air we can ? The reason we run so "poor" at max torque rpm (around 2,000 rpm) is the turbo has a big reserve at this rpm, it would be possible to observe richer A/F before turbo provide a correct boost and toward the end of its boost@rpm curve ?

Regards

GSX

[J. Edlund]

Originally posted by GSX-R


Do you mean that boost pressure on modern turbo diesel is rarely (never ?) controlled by the ECU ?The turbo is only regulated for a max rpm limit OR boost pressure ? The reason why we ear the turbo in action when we press the pedal is just because we burn more fuel and so exhaust pressure run the turbo (no wastegate control until boost pressure/turbo rpm ) ?

The goal would also be to run with the more air we can ?

Regards

GSX

Originally posted by J. Edlund
boost pressure is calculated from a map based on rpm and fuel added, this value is then corrected by the atmospheric pressure.

The above refers to electronic control of the boost pressure. Often the turbocharger is of variable nozzle type, so boost is controlled by changing the nozzle area. Vacuum from the vacuum pump or an electronic actuator can be used to do this.

The turbine that powers the compressor is a heat engine like any other, increase the temperature and/or massflow and the power output increase. With more power, the compressor can supply more air at a higher pressure to the engine.

[GSX-R]

Isn't possible to slightly improve BSFC at 2,000 RPM for example by slightly reducing boost pressure and reducing A/F ratio when turbo pressure is quite high and when turbo can sustain a higher temperature. Turbo energy is not 100% free,isn't it.

P.S : An article about boost pressure, EGR and VGT from Jacque Gordon (March 2005)

http://www.motorage....208/article.pdf

[J. Edlund]

Originally posted by GSX-R
Isn't possible to slightly improve BSFC at 2,000 RPM for example by slightly reducing boost pressure and reducing A/F ratio when turbo pressure is quite high and when turbo can sustain a higher temperature. Turbo energy is not 100% free,isn't it.

P.S : An article about boost pressure, EGR and VGT from Jacque Gordon (March 2005)

http://www.motorage....208/article.pdf

BSFC goes down as boost goes up, that is given the turbocharger efficiency maintains at a high level.

The energy supplied to the turbo is free, using that energy can however come at a small cost as the turbine is restrictive to the exhaust flow. However, when turbocharger efficiency is high, the increase in exhaust pressure is equal or smaller to the increase in inlet air pressure. Also, as boost is higher, the engine can running using a leaner air/fuel mixture thus improving efficiency, or by develope more power in which case the friction loss becomes smaller in relation to bmep, thus also improving efficiency.

On gasoline engines it has been tested to open the wastegate at part load to reduce the restriction caused by the turbine, the effect on fuel consumption is marginal at best. There was also a test done by NACA, they measured the engine power with and without a blow down turbine attached, the powerloss with the turbine was marginal.

With diesel engines turbocharging is a win-win situation, with gasoline engines it tends to be a win-lose situation.

[GSX-R]

Thank you.