Why no small diesel trucks?

[bigcozy]

I got interested in diesels after wrenching on heavy equipment putting myself through engineering school. The thing that impressed me the most about them was durability under load. I have seen diesels that lasted several hundred thousand miles, and I have seen them lock up at less than 200K (one was a Mercedes 240 no less). Overseas, you see cars and light trucks that have almost no body left, but the engine keeps chugging. When you open the hood, half the parts will be fabricated.

I read some time ago that BMW had a non turbo diesel that had very fast pick up, but it wasn't selling well in Europe, and no hope for bringing it to US. The US market for diesels is pretty focused, not many soccer moms want to deal with the smell, the noise, the black cloud or the slow SUV. There is a core non commercial market for them, but it seems it is only larger trucks, and small cars get them. Chrysler has a PT Cruiser that is supposedly shipping now that has a diesel, sounds like the answer to a question no one asked.

 

[KC2IXE]

I worked on 2 of the Mid 80s GM diesels - Both in Delta88s. Frankly, they got a bad rap in that car because they had a few problems

1)They had the absolute WORST water seperators I've ever seen. Darned things clogged up every 1000 miles or so
2)They were gas engines changed around to be diesels they didn't hold up

It was an interesting time. In that year, 2 of my bosses bought the diesel Delta88s, my Mom and Dad bought a Gas Delta 88, and my bosses also bough a diesel truck. The truck was fine (who knows where it is now, 20 years later), both diesel Deltas were gone within 4 years. My Mom and Dad's Delta? Dad's still driving it! It was "Mom's" car. They bough a new car just before Mom retired, and Dad started driving the Delta. Mom's new car went way 2 or so years ago, and she has another new one. The Delta keeps going

As for folks not keeping up with the technology - remember, a LOT of car buyers still thing the best cars EVER made were made in the mid to late 1960s. Big engines, easy to work on, high horsepower.

Of course, they don't seem to remember having to do tuneups every 10k miles or less, and it was an event when you got 100k miles on the car (Pull over to the side of the road and party)

 

[Blikbok]

ikendu and DieselDave: That's one of the great advantages of serial hybird cars-- the root power source is irrelevant /ubbthreads/images/graemlins/smile.gif In a few decades, you could swap the diesel for hydrogen or fusion.

 

[Eugene]

Some of those early GM diesels were gas engines converted to diesel which is why they had so many problems and had so low power. The better GM ones like the 6.2 and 6.5 were much better but unpopular due to the bad rep from earlier. I would love to have a nice 4 cyl Diesel in my S-10 to replace the 2.2L gas egine in it, you can't get any slower /ubbthreads/images/graemlins/smile.gif Marketing is one thing that hurts diesels, poeple think they will have a big cloud of black smoke behind them like busses do and see the lower HP numbers as compared to a cheaper gas engine. Their is a big marketing war over horsepower. All the makers keep trying to get big hp numbers to be better than the next. The general public wants the car with more horsepower than the next. Only problem is people don't realize is torque is what moves a vehicle, horsepower makes noise /ubbthreads/images/graemlins/smile.gif. Just get stuck behind the little car with the coffee can exhaust and all the stickers that add horsepower /ubbthreads/images/graemlins/smile.gif

 

[Blikbok]

But will the stickers increase my fuel efficiency?
The HP vs Torque war sounds similar to the MHz war with computers.

 

[NewsFlash]

Diesel technology getting better doesn't just apply to automobiles, it applies to locomotives as well. All new locomotives, AFAIK, are available with electronic fuel injection. The good thing about this is that emissions can be controlled better because of it, so the locomotive company reps tell me.

Not only that, the government regulations on diesel locomotive emissions is here to stay. Locomotives made before a certain year never have to meet the new guidelines. Locomotives made after that certain year don't either, unless you overhaul them, then they must meet the 1st level guidelines. Then starting about the year 2000 began 2nd level guidelines and then eventually will be 3rd level. This amounts to changing the injector pumps and nozzles at regular intervals, not to mention governors and turbos I believe. Also update software for electronic fuel injection. Not to mention close inspection of the engine block.

Since this happens to locomotives, I can only imagine the hoops the auto manufacturers have to jump through on emissions. /ubbthreads/images/graemlins/ohgeez.gif

 

[Kristofg]

>Chrysler has a PT Cruiser that is supposedly shipping now
>that has a diesel, sounds like the answer to a question no
>one asked.

I tried that model last week. It's a 2.2 litre Mercedes Common Rail Turbo Diesel engine. It's quite good actually, but has a lousy gearbox and turning circle. It's performance is comparable to the 1.9 litre volkswagen TDI with the Red DI (115 HP). 0 to 100 KMH in about 12 seconds. The downside is that it goes quite high in RPM to achieve good acceleration.
It's quite fun to drive and feels quite sporty though. It's one of the few US cars which starts to sell quite well over here (belgium) especialle with the current dollar exchange rate.

 

[SilverFox]

Concerning Horsepower and Torque, I ran across this definition of power that may provide some useful information.

"Horsepower and Torque:

Power is the rate at which work is done. When the engine torque is turning the crankshaft and power is being delivered, the resulting horsepower may be expressed as:

hp=(2*pi*t*rpm)/33000

which can be simplified as

hp=(t*rpm)/5252

where: hp = horsepower, hp
t = torque, ft-lbs
rpm = engine speed, revolutions per minute


This is a great formula. Basically it says that if you can keep the same amount of torque, then the more rpm you can turn, the more horsepower you get!

That's why Formula One and CART and IRL engines all turn incredible rpm. The faster the engine turns, the more power it can make (when it is properly tuned to operate at that speed).

Consider for example: a normally aspirated internal combustion engine typically produces about 1 to 1.5 ft-lbs of torque per cubic inch when it is properly tuned to operate at any specific rpm. With a 2 litre (1 litre is about 61 cubic inches) engine, producing 1.5 ft-lbs of torque per cubic inch, you would expect to get about 180 hp at 5200 rpm... but you will get a whopping 415 hp if you can get it to run at 12,000 rpm.

The 3.5 liter IRL engine is reported to produce about 650 hp at 10,700 rpm. That would be about 1.5 ft-lbs per cubic inch.

The Ferrari 3.0 liter Formula One engine is rumored to produce about 860 hp at 18,500 rpm. That would be about 1.33 ft-lbs per cubic inch.

And at the other end of the rpm spectrum, one model of the 360 cubic inch four cylinder Lycoming IO-360 aircraft engine produces 180 hp at 2700 rpm, which is 0.97 ft-lbs per cubic inch.

In general, production automobile engines that have a broad torque band will produce about 0.9 to 1.1 ft-lbs per cubic inch. Highly tuned production engines, such as the Honda S2000 or the Ferrari F50 are in the range of 1.1 to 1.3 ft-lbs per cubic inch. Highly tuned race engines such as NASCAR, IRL and Formula One are often in the range of 1.3 to 1.5 ft-lbs per cubic inch."

Tom

 

[avusblue]

I've always been sort of a "car guy", but this torque vs. HP thing has always kinda confused me. Shouldn't gearing neutralize this? I know that in the real world it doesn't. My question is, why?

Let me put it another way. Let's say we take 1) a diesel truck engine that generates 200 horsepower but incredible low end torque. And let's take 2) an American middle of the road V-6 car engine that generates 200 horsepower and commensurate torque. Lastly, take 3) a Honda racing motorcycle engine that generates 200 horsepower at very high rpm but less torque at low rpm.

Pretend each engine weighs the same and is installed in the same vehicle.

In the real world, car 1 accelerates fast from 0 - 15 then levels off, car 2 accelerates "normally", and car 3 is slow off the line and then screams.

If each engine produces similar total power, why can't you apply drastically different gearing to each engine to achieve the same essential result? If for example, we pretend that a 12 speed automatic transmission existed, giving a broad enough spread of gear ratios from very low to very high, could each engine deliver equivalent performance.

I don't think so, but I don't understand why not.

Thoughts?

 

[Eugene]

Thats pretty much it, I way over simplified it. Those engines in the coffee can exhaust car make all their torque and hp at the high end of the rpm range, thats why you hear them buzz so much, they have to be geared to keep the rpm's high. Diesel engines have a relatively narrow rpm range therfore thier torque and hp curves are realitively flat, thats also in part why they are more efficient. The wider rpm range the less you start to loose efficenecy at either end.
I think that we should build cars similar to the locomotives. Use a Small Deisel engine under the hood that has a narrow rpm range and it very powerful and efficient in that range, the couple it to a generator. Then use that power to ru an electric motor in each wheel.

 

[2dogs]

One thing that always starts my head shaking in wonder is when someone, like my neighbor about a week ago, buys a full size pickup truck with a gas engine. He just bought a Cheve 3/4 ton crew cab with a gas engine. He works as a contractor and is always in his truck. He sold off the 1 year old H2 and bought this truck. I guess he forgot to consult with me.

On our little one block street there are 7 diesel vehicles between 4 families. Some mornings it sounds like downtown Iraq. Sounds like... victory!

 

[NewsFlash]

Eugene,

I second that! /ubbthreads/images/graemlins/thumbsup.gif

The cool thing about that is cars could do just like the locomotives. Most people don't know locomotives have 8 throttle notches, or 8 levels of power output. That used to mean 8 different engine speeds, but with newer locomotives that ain't always so! The alternators (used to be generators) are constant kilowatt output at any given throttle notch. At low speed, the traction motors want to see lots of current (torque proportional to current) and as road speed increases they want to see higher and higher voltage (to fight the back emf being produced). With a big enough alternator you can have all the current you need or all the voltage you need, just not at the same time.

Then there's the dynamic braking used on locomotives. Now that stuff is some kinda neat! /ubbthreads/images/graemlins/cool.gif

 

[Moat]

avusblue -

Now, I'm not absolutely certain, but I believe the HP/torque/RPM relationship to diesels being "slow", or "lower power" than comparably sized gas engines, has a lot to do with the relatively low volatility - or slow "evaporativity" - of diesel fuel vs. gasoline.

For a liquid fuel to burn, it must first be vaporized - and that takes time. A small amount of time, for sure, even when subject to the high temps and pressures of a diesel's combustion chamber. But it still takes considerably longer than gasoline.

As an engine's speed increases, the available time between injection/ingestion of the atomized fuel "mist" and the period of ignition grows shorter, and eventually at some point the fuel will be ignited before it has had the chance to evaporate fully, or may not ignite at all - resulting in excessive HC emissions and a self-RPM-limiting loss (tapering off) of combustion pressure, thus power.

Gasoline - capable of considerably higher rates of evaporation - will run up against the same barrier, but at a much higher RPM.

Since power (horsepower) is directly proportional to RPM (double the engine speed, double the HP), this speed/time limitation of diesel fuel vaporization creates an inherent RPM - and therefore horsepower - limitation in diesel engines, when compared directly to gasoline engines of equivalent displacement.

High RPM race engines burn specially formulated, highly volatile race fuels designed to evaporate in the extremely short amount of time available at the stratospheric RPM's where they normally operate. Oftentimes, modern race engine fuel injector nozzles are located WAY upstream of the inlet valves - sometimes located well up and outside of the inlet manifold's bellmouth entrance - in order to provide the fuel as much time as possible to vaporize completely.

And since you can't increase horsepower by spinning a diesel beyond that barrier, the only other option to increasing power (to that comparable of a gasoline engine of the same displacement) is to increase the torque produced (by the pressure of combustion) by the addition of more fuel/air mixture - hence turbocharging, a means to force more power-producing charge into the engine at pressures above what the atmosphere can alone provide.

And from what I understand, some of these turbo-diesel cars are just about as fast as their gasoline counterparts.

Diesel compression/combustion pressures are significantly higher than that of gasoline engines, which is why they are known as such "torquers". But when called apon (like in a passing situation), it's the engine's ability to make the MOST POSSIBLE torque at the HIGHEST POSSIBLE RPM that ultimately determines the available power (and the expression on the faces of oncoming drivers /ubbthreads/images/graemlins/ooo.gif ). In that case, naturally aspirated diesels are at a disadvantage. The BMEP advantage is not enough to make up for the vaporization/RPM constraints.

All AFAIK, anywho... (well, me and Kevin Cameron... /ubbthreads/images/graemlins/blush.gif)

Bob

 

[avusblue]

Bob, I agree with everything you said. My question remains, why can't the diesel be geared to use its prodigious low rpm torque to produce the same output at the drive wheels as a high rpm gas engine with different gearing.

Remember, in my hypothetical situation, both engines produce 200 hp. They just do it at different crankshaft speeds. Yet the rear wheels turn at the same speed on each; the difference is the gearing.

I know that in the real world, the high rpm engine tends to accelerate better -- I just don't understand quite why if the power being produced is the same.

Maybe its just one of those many things that humans arent' meant to comprehend.

Dave

 

[NewsFlash]

avusblue,

I'm of the opinion that what you're saying would work, just look at the diesel tractor trucks on the highway. Some of them have as many as 18 gears, so I'm told. I just don't think the auto manufacturers would go to the trouble of building that type of transmission (like you're suggesting) and then couple it to a relatively small engine (2.2L).

OTOH, my father-in-law has a late model GMC (I think it is) 2500 HD truck, and I have noticed the rpm range is very narrow. He has a fifth wheel camper and he has no problem pulling it. I take it the transmission is very well designed for the job.

 

[Moat]

It's really quite simple...

Actually, according to your hypothetical situation - the diesel WOULD produce the same output at the drive wheels as the others. But that's not the real world...

You said: "I know that in the real world, the high rpm engine tends to accelerate better -- I just don't understand quite why if the power being produced is the same"

In the real world, a gasoline engine of equivalent HORSEPOWER (torque x RPM) to a diesel would be much smaller and lighter. In fact, it would fit in a smaller, lighter car. Hmmm.... a smaller, lighter car - with a smaller, lighter engine of the same power..... hmmm...

Apply a dash of Newton's law's and..... Voila!
I think that's probably your real world answer! /ubbthreads/images/graemlins/smile.gif

In reality, I think in most vehicles that have the option of either gas and diesel engines, the diesel will not develop the HORSEPOWER that the gas engine does (maybe the torque - maybe even MORE torque - but it's horsepower that counts). And even if the power was the same, the overall weight gain of the diesel installation would likely be the cause of lack of acceleration/power that folks mention (and the narrow powerband NewsFlash described above makes accessing that power more difficult).

Now, that last paragraph is just an educated guess, as I don't have any vehicle performance figures at hand. I'll try to find some weight/power/acceleration/etc... figures to prove my point...(to myself, as well!)

Bob

 

[Blikbok]

It may also be an issue of the size efficiency of the power plant. Electric power is amazing in small applications, while nuclear power isn't realistic below a certain size. I've always assumed, much like 2Dogs, that once the vehicle goes above 2 tons curb weight, it should be diesel.

 

[AilSnail]

A friend has a beetle with porche 80hp boxer, really a mean torque and ooh such a nice sound. Makes me wonder what a boxer diesel could crank.

 

[ikendu]

On the other hand... /ubbthreads/images/graemlins/smile.gif

My Golf TDI accelerates "acceptably" and I am rewarded with excellent mileage and fuel which curently is 21 cents a gallon CHEAPER than gasoline. Not to mention that I can run a completely renewable fuel if I wish (biodiesel) or blend it with petroleum if I wish.

Cheaper fuel, better mileage, renewable alternatives... all good. /ubbthreads/images/graemlins/smile.gif

 

[Kristofg]

Comparison time then:
Audi A3 (about the same as the Volkswagen Golf)

Gasoline engine 1.6 litres 102 HP 75 KW (KiloWatt)
Acceleration 0-100KMH (0-60Mph) 11.9 seconds
Torque 148 Nm at 3800 RPM

Gasoline engine 2.0 litres 150 HP 110 KW
Acceleration 0-100KMH (0-60Mph) 9.1 seconds
Torque 200 Nm at 3500 RPM

Diesel engine 1.9 litres 105 HP 77 KW
Acceleration 0-100KMH (0-60Mph) 11.4 seconds
Torque 250 Nm at 1900 RPM

Diesel engine 2.0 litres 136 HP 100 KW
Acceleration 0-100KMH (0-60Mph) 9.6 seconds
Torque 320 Nm at 1750-2500 RPM

The diesel and gasoline engines differ very little in weight.

Correct me If I'm wrong, but i seem to remember from physics class that a Diesel engine uses it's huge Torque to accelerate a car fast at low RPM, while a gasoline engine accelerates fast at high RPM, resulting in high HP. Which results in more wear on the gasoline engine because it has to turn more often and hence a shorter life-span.