Why arent Diesel Cars Supercharged??

porsche_fan · 5th April 2007, 21:57

no diesel automotive engine in serial production can run A/F ratios of 90:1, or 30:1. In fact the A/F ratios are more around 22:1 at full load and 40:1 at no load.

at this lean a mixture there would be tremendous knocking and it would also be very difficult to meet emission norms (NOx production).

Diesels are more compatible with TC because of the fact that they run at high CR. Diesel engines are knock limited by speed. Petrol engines, by CR. When you turbocharger, very broadly speaking, you are increasing the effective CR of the engine. This is something a diesel engine can handle without much problems, but is real pain for petrol engines.

The Wolf · 6th April 2007, 02:23

If its turbo chargers that produce better usable power and lesser parasytic losses I wonder why funny cars which do under 7sec quat miles use superchargers!!!!

v1p3r · 6th April 2007, 02:25

Quote:

Originally Posted by The Wolf

If its turbo chargers that produce better usable power and lesser parasytic losses I wonder why funny cars which do under 7sec quat miles use superchargers!!!!

I would guess it comes down to two things. Lag and more linear power delivery.

BUSA · 6th April 2007, 02:31

Thanx guys for your inputs.

What about adding a Supercharger for lower end and Turbo for upper end buttt then Diesel dont have high end as such, max they go is till 5000RPM.

v1p3r · 6th April 2007, 02:33

Quote:

Originally Posted by BUSA

What about adding a Supercharger for lower end and Turbo for upper end buttt then Diesel dont have high end as such, max they go is till 5000RPM.

VGT has negated the need.

porsche_fan · 6th April 2007, 16:37

Quote:

Originally Posted by v1p3r

VGT has negated the need.

and 2 stage systems!!!

jat · 13th April 2007, 19:14

Both, super-chargers and turbo-chargers, adds to the power of the engine by forcing more air for burning more fuel in the cylinders. And both can be used on petrol or diesel, alone or in combination. And in principle they don't affect the efficiency.

Why diesels are turbocharged? Basically, the turbochrger is more ideal system as it is freewheeling (not mechanically connected to engine). Therefore it can ideally match the air fuel ratio over a longer rpm range. Also any change in load will affect the engine rpm - torque may increase and rpm may reduce but power may be same (example changing of gear, going on slope). As power demand is same, the air demand will remain same. As turbocharger is not mechanically connected, it will continue to supply almost same amount of air, whereas mechanically connected supercharger will reduce the air and hence the power.

The reason why it is not popular with petrol engines is that the lower exhaust pressure at low load will cause higher turbo-lag and will considerably degrade the performance. Even worse that diesels at startup. Would you like to buy such car? On the other hand, due to spark ignition, the petrol engine have the advantage of higher operating rpm range and therefore using direct driven blowers are not able affect that much the operating range, as it would do in diesel engine.

Why combination is not used? Well ask the marketing gurus. They build vehicles for mass use and not for few guys who would prefer performance over anything else. (Combination will increase complexity, manufactering and maintenance costs etc.)

PS: Bigger diesel engines, manufactered entirely on the basis of economy has turbos matched to a very narrow operating band and at starting use a electric blowers or two blowers.

5th April 2007, 21:57	#16
porsche_fan BHPian Join Date: Mar 2005 Location: Epinal,France Posts: 83 Thanked: 9 Times	no diesel automotive engine in serial production can run A/F ratios of 90:1, or 30:1. In fact the A/F ratios are more around 22:1 at full load and 40:1 at no load. at this lean a mixture there would be tremendous knocking and it would also be very difficult to meet emission norms (NOx production). Diesels are more compatible with TC because of the fact that they run at high CR. Diesel engines are knock limited by speed. Petrol engines, by CR. When you turbocharger, very broadly speaking, you are increasing the effective CR of the engine. This is something a diesel engine can handle without much problems, but is real pain for petrol engines.
	() Thanks

6th April 2007, 02:23	#17
The Wolf Senior - BHPian Join Date: Jan 2005 Location: Bangalore Posts: 1,119 Thanked: 76 Times	If its turbo chargers that produce better usable power and lesser parasytic losses I wonder why funny cars which do under 7sec quat miles use superchargers!!!! Last edited by The Wolf : 6th April 2007 at 02:24.
	() Thanks

6th April 2007, 02:31	#19
BUSA Senior - BHPian Join Date: Aug 2005 Location: Bombay Posts: 5,127 Thanked: 23 Times View My Garage	Thanx guys for your inputs. What about adding a Supercharger for lower end and Turbo for upper end buttt then Diesel dont have high end as such, max they go is till 5000RPM.
	() Thanks

13th April 2007, 19:14	#22
jat BHPian Join Date: Dec 2005 Location: SINGAPORE Posts: 266 Thanked: 7 Times	Both, super-chargers and turbo-chargers, adds to the power of the engine by forcing more air for burning more fuel in the cylinders. And both can be used on petrol or diesel, alone or in combination. And in principle they don't affect the efficiency. Why diesels are turbocharged? Basically, the turbochrger is more ideal system as it is freewheeling (not mechanically connected to engine). Therefore it can ideally match the air fuel ratio over a longer rpm range. Also any change in load will affect the engine rpm - torque may increase and rpm may reduce but power may be same (example changing of gear, going on slope). As power demand is same, the air demand will remain same. As turbocharger is not mechanically connected, it will continue to supply almost same amount of air, whereas mechanically connected supercharger will reduce the air and hence the power. The reason why it is not popular with petrol engines is that the lower exhaust pressure at low load will cause higher turbo-lag and will considerably degrade the performance. Even worse that diesels at startup. Would you like to buy such car? On the other hand, due to spark ignition, the petrol engine have the advantage of higher operating rpm range and therefore using direct driven blowers are not able affect that much the operating range, as it would do in diesel engine. Why combination is not used? Well ask the marketing gurus. They build vehicles for mass use and not for few guys who would prefer performance over anything else. (Combination will increase complexity, manufactering and maintenance costs etc.) PS: Bigger diesel engines, manufactered entirely on the basis of economy has turbos matched to a very narrow operating band and at starting use a electric blowers or two blowers.
	() Thanks