Supercharging a Diesel

[NSXType-R]

This is freaky - I was just wondering about this earlier (trying to think of an example of an s'charged diesel car engine), then I log onto UCP and it's at the top of the screen...

...I'm a psychic!

No, just pure luck maybe?

[ripper46]

I hunt, and kill TDI's

[henk4]

I hunt, and kill TDI's

well, to everybody his mature hobby.

[ripper46]

well, to everybody his mature hobby.

, seriously now, In the last few years I've learned to like diesels, I think they are veryy usefull, and... who knows maybe I'll buy one some day.
But I prefer the joy of a high revving petrol for now

[Clivey]

A small piecce of advice for anyone that's thinking about buying a diesel car:

Make damn sure you buy one that's powerful enough! Don't just believe the promises for massive fuel economy from base-models. I drive the 80ps (74BHP) version of Opel/Vauxhall's 1.7CDTi Astra and it struggles to pull the car! It may have 140lb/ft of torque, but seeing as that's only available between about 2-3k rpm, you have to constantly thrash it and change gear so often that your arm gets tired. I said "don't believe the promises for massive economy...", and that's because when you have to thrash the gutless base model diesels to get the car to move, fuel economy disappears.

I'm glad I didn't choose to buy my current car (details of how it came into my posession here: http://www.ultimatecarpage.com/forum...4382-deal.html), because it frustrates me immensely. I'm currently considering a 1.9CDTi (150ps) Astra as my "proper" new car.

[henk4]

A small piecce of advice for anyone that's thinking about buying a diesel car:

Make damn sure you buy one that's powerful enough! Don't just believe the promises for massive fuel economy from base-models. I drive the 80ps (74BHP) version of Opel/Vauxhall's 1.7CDTi Astra and it struggles to pull the car! It may have 140lb/ft of torque, but seeing as that's only available between about 2-3k rpm, you have to constantly thrash it and change gear so often that your arm gets tired. I said "don't believe the promises for massive economy...", and that's because when you have to thrash the gutless base model diesels to get the car to move, fuel economy disappears.

I'm glad I didn't choose to buy my current car (details of how it came into my posession here: http://www.ultimatecarpage.com/forum...4382-deal.html), because it frustrates me immensely. I'm currently considering a 1.9CDTi (150ps) Astra as my "proper" new car.

just get it chipped...

[Clivey]

just get it chipped...

I would, but the exterior's not in the best condition either (if it were to be restored to "good" condition it'd need the front offside (right) wing replacing and nearly every panel respraying - so it'd be easier to just get rid of it and buuy something else. Then chip that.

[drakkie]

If i had the money i would buy a Turbo Diesel.. Did your instrutor like you pulling wheelies


MAZDA BT-50 B2500 DX details - CarPoint Australia

If I had it too, i'd definately do it. When this engine is beyond repair or something, I will put one in the Alto. The instructor was really relaxed actually. He let me drive higher speeds on the motorways too sometimes, however that was after around 15 lessons. My top speed was 160 km/h or 100 m/h. As long as I'd watch out for police, it was fine. The instructor was from Rozenburg, crazy folks there

I hunt, and kill TDI's

We Dutch, in our infinite wisdom, were right when we started the jokes about dumb and crazy Belgians

[ripper46]

I bet we have way more jokes about the dutch

[Clivey]

Back to the original question: How come there aren't any supercharged diesel production cars? I'm really interested to know the answer to this...

[rovman]

Guys I hate to tell you this but they were turbo supercharging diesel engines a long time ago, and it is still done today. They feed the trubo into a the air inlet of the supercharger then to the motor. The boost from the turbo gives you almost immediate resopnse from the supercharger. There is a few individuals who have done this on their diesel pickup trucks. I have one friend who is in the process of installing this type of system on his power stroke. Even though I am not a fan of the power stroke this is wht he is using.

Keep in mind both the turbo and supercharger have losses due to friction, but the addtional hp gained from the systems is over and well beyond those losses. Remember to feed you air flow across a cooler of some sort. Or use a hydrogen/air mix or nitros/air mix to keep the air temp down plus as a side benifit you will get a better burn of the diesel. Diesel engins loves the air inlet temp between 70-90 deg F, but you will want to play around with this area to find the right temp for your motor. The cooler the air the more can be packed into the chambers leading to better effecient.

[LeonOfTheDead]

Hi rovman,
I suppose he was just referring to the fact that all production diesel cars are equipped with turbochargers as opposed to superchargers. We have VGTs, twin turbos, but not a supercharger on production cars.
After market or tuning is a whole different story though, as you pointed out.

[henk4]

Guys I hate to tell you this but they were turbo supercharging diesel engines a long time ago, and it is still done today. They feed the trubo into a the air inlet of the supercharger then to the motor. The boost from the turbo gives you almost immediate resopnse from the supercharger. There is a few individuals who have done this on their diesel pickup trucks. I have one friend who is in the process of installing this type of system on his power stroke. Even though I am not a fan of the power stroke this is wht he is using.

Keep in mind both the turbo and supercharger have losses due to friction, but the addtional hp gained from the systems is over and well beyond those losses. Remember to feed you air flow across a cooler of some sort. Or use a hydrogen/air mix or nitros/air mix to keep the air temp down plus as a side benifit you will get a better burn of the diesel. Diesel engins loves the air inlet temp between 70-90 deg F, but you will want to play around with this area to find the right temp for your motor. The cooler the air the more can be packed into the chambers leading to better effecient.

Welcome.
Interesting, but this sounds more like "aftermarket". Who are "they" in your post? Are you aware of any OEM system is this field? Can you give us some figures on additional power/torque because of the SC?

[culver]

I know the old GM 2 stroke locomotive diesels were supercharged. I suspect that we generally see only turbo diesel auto engines because the turbo is particularly well suited for a diesel. Diesels don't have throttle plates. That means that even when you let off the gas the engine is still flowing just as much air (so long as the revs don't change). That works nicely for a turbo. As I understand it, and I am a bit fuzzy on this, the problem with the throttle plate closing is it creates a momentary high pressure region between the turbo compressor outlet and the throttle plate. This is why you have the blow off valve. However when you blow off that pressure you waste the inertial energy in the turbo. It now takes a moment or two to spool back up to generate pressure again. This isn't a problem with a supercharger as their speed is related to crank speed. This also isn't a problem with diesels as they don't have a throttle plate. So if you momentarily fully back off the "gas" the only thing that causes the turbo to slow down is the reduction in exhaust gases on the turbine side. There is no increase in pressure on the compressor side. Thus a diesel engine is less affected by one of the big issues with turbos when mated to gasoline engines.

I suspect their are a few other reasons as well. Diesel engines are quite happy at high boost levels. A low pressure car turbo might only boost to say 1/2 atmosphere (~7psi). A moderate boost might reach 1 full atmosphere. A really high pressure gasoline turbo would be 1.5 atmospheres. Diesels will do that all day. Diesels really really like the high pressure. I don't believe (but could be wrong) that positive displacement type blowers are that good at doing high pressure boosting. I think they are better for lower boost levels that are well suited to gasoline motors. The centrifugal compressors used on turbos are well suited to the higher boost pressures that diesels like.

Finally, I don't think there is a huge cost difference between a supercharger and a turbo. I've never seen pricing data but this is speculation based on the cost of aftermarket FI kits for cars. It seems like the turbos are no more expensive. If that is true then it would make sense for a diesel engine manufacture to use the system that was best suited for diesels. When it comes to gasoline motors we can see the market hasn't decided one is all around superior to the other (ie we have both SC and turbo cars). When it comes to diesels it is reasonable to assume that turbos seem to be the best setup for automotive diesels. Heck, that seems to be true to the point where I don't think you can buy an automotive diesel without a turbo. Certainly the gasoline world is no where near as unanimous as we have turbos, SC and none of the above.

I know this isn't a complete answer but I hope it helps.

[Clivey]

I'm starting to lose a little love for the engine in my car...

...people say that turbo diesels have lots of low down torque: That's absolute rubbish - ALL of the power and torque is in the mid-range.

Whilst it's true that most modern single-turbo diesels offer a better performance/running cost ratio than the equivalent petrol model, no modern diesel can get close to matching a good petrol engine for sheer driving pleasure. All of the performance of the single turbo units is concentrated into a very narrow powerband (usually 2-4k rpm), and as a result, the power/torque curves usually look like this:


- This is actually the engine I have in my C4.

What this means is that:

• <2,000 rpm: Get out and push
• 2,000-4,000 rpm: Slug of torque = good acceleration
• 4,000+ rpm: Rate of acceleration drops rapidly - you accelerate faster if you change up at 4,500rpm and drop into the powerband in the next gear.

So on paper the power/torque curve looks very much like an early turbocharged petrol engine, except with more drop-off at the top of the rev range. The catch with a diesel is that it is vital to have the turbocharger on boost if you want to accelerate. A petrol turbo will at least do some accelerating when it's "off boost" - whereas a diesel off boost is as lethargic as I am at 04:00 AM.

Twin sequential turbo diesels are much better (I am very impressed with BMWs 123d) - the epic turbo lag is very much reduced and there's less drop-off above 4krpm, but they still don't offer the flexibility, responsiveness or pleasant sound of a nice petrol engine.

At this point, you may be thinking: "Well it's just turbo lag; You can work around it"...and it's true: You can.

But it's not particularly helpful. Or pleasant to drive.

The main problem (at least in my car) comes in town driving when you're in traffic, at junctions or when you have to climb a hill without a run up. In these situations, you often find yourself slowing down in 2nd or 3rd gear, for example: approaching a junction. What happens next is that you see a gap in the traffic at the junction and decide you can pull-out and carry on. Let's say you're in 2nd gear and doing 10 mph at this point...you go to accelerate and...






...nothing.


...That gap is getting smaller. Foot to the floor...


...


...


...this is getting uncomfortable now...


...


...BANG! Power arrives as the turbocharger finally wakes up. - ****! That was close!

Now admittedly, the gearbox in my car is half the problem: 50% of the time it resists you selecting 1st gear unless the car is almost stationary (<5mph). The catch is that if you're doing anywhere below about 1,800 rpm in the next gear and it can take several seconds to get going. This is on a flat road - hills (lots of them where I live) make the problem MUCH worse. And it's amplified again if the engine's cold.

The only solution is to dip the clutch as you approach a junction, and if you see a gap, rev the engine to over 2k rpm and slowly let the clutch back in to ensure you have enough boost...but my feeling is that you really shouldn't have to do this in the first place.

However despite all of this, my car remains an ideal daily driver at the moment. My daily drive to work is 12 miles long on busy urban and country roads with plenty of hills and juntions, yet I still get around 40 mpg (Imperial). If I were driving the equivalent petrol, I'd probably only get around 25 mpg from an engine with basically the same outright performance.

I still think that the diesel was the best choice for me, balancing performance, running costs and the cost of insurance...

...but I still want a quick petrol next time though!