Oil & Fuel General diesel question

[irvingj]

John_bud-- thanks for being gracious. Yes, gas engines also can have long strokes-- the David Brown designs of the 50s & 60s come to mind. The guy designed tractor engines, but also the twin OHC 6-cylinders used in Aston-Martins (hence, the "DB6, DB7," etc.). The '52 XK120 Jag I grew up with was similar; gobs of torque at low rpm. I was mainly referring to the lower exhaust temps (and greater mechanical efficiency as a result) diesels enjoy...

Redneck- I'm not up on all the changes in diesels over the past 20 yrs or so, but I do know there's a WORLD of difference between the '82 Peugeot 504D wagon I had for a while and the '05 TDI Jetta wagon I now have- that little VW will chirp (or smoke) the tires in all 5 gears if it's pushed hard-- and a Jetta TDI set new world records for the Pike's Peak hillclimb recently. (Seems I read somewhere that "Peugeot" was French for "slow"...)

It's sad to see that most any other industrialized country has such a higher percentage of diesels than we do here-- in Europe, even model airplane engines are about 50% diesel. I'm just waiting for a breakthrough in waste biomass diesel production-- a lot of progress has been made so far.... John_bud-- as you can see, I invented verbosity! With apologies, Walt

 

[john_bud]

J

It's sad to see that most any other industrialized country has such a higher percentage of diesels than we do here-- in Europe, even model airplane engines are about 50% diesel. I'm just waiting for a breakthrough in waste biomass diesel production-- a lot of progress has been made so far.... John_bud-- as you can see, I invented verbosity! With apologies, Walt

I agree completely that the "powers that be" in our government as well as the pressure groups have tied the hands of both the auto companies as well as consumers. Looking at it from a different angle, the "greenies" are always pointing to the EU as the end all be all of eco friendliness. Yet, the EU has MUCH much MUCH looser exhaust emissions laws than we do and they thus use much less fuel than we do per mile traveled. They also paradoxically, have both the ultra high end 250mph and the 100 mpg 800 pound machines. Neither of which they are allowed to sell here due to our idiots ---er --- politicians. In fact, we can't even sell many more diesels as the refineries have been optimized to produce gasoline at the expense of diesel. Now they are short of diesel, but have too much gas.


I don't know if you have invented it, but I am trying to improve it with the addition of tautologous adders to the verbosity.

jb

 

[Reg]

They ALL have computers (-:

Some are analogue and are implemented as relatively simple linkages, but they're still computer control systems.

Gas engines (carburetor) are regulated by an air restriction (hence the name throttle).
The amount of air flow determines the amount of fuel that is vaporized into the air stream - more air + more fuel = more power {Greatly simplified}

Diesel engines (generally) are regulated by controlling how much fuel the injection pump sends to the cylinders, the air stream is "fixed' or wide open. Diesels have been "fuel injected" for a very long time now, although I think the first engines ran on coal dust and I don't know how that was delivered to the cylinder(s).

Turbo and superchargers increase the mass of air by compressing it, allowing more fuel to be burned at the same air/fuel "mix" ratio.

 

[john_bud]

They ALL have computers (-:

Some are analogue and are implemented as relatively simple linkages, but they're still computer control systems.
.

Are you saying that the flyball governor is a computer of the analog flavor?

Never thought about it in that light, it may stretch the bounds of "computer" a bit.

 

[SnowRidge]

Are you saying that the flyball governor is a computer of the analog flavor?

Never thought about it in that light, it may stretch the bounds of "computer" a bit.

A bit?

 

[Mickey_Fx]

Boy, lots of comments. Some with repeat info, others clarifying an answer from a question, etc.

One thing not mentioned so far is combustion chamber design in diesel engines. Close 3 decades ago when I was reading up on diesel engine design, there were at that time 5 combustion chamber types, each with their own operating characteristics. Some designs permit high speed (close to gas engine speeds) operation, others that permit low compression ratio's not much higher than was common 20-30 yrs ago in gas engines. I seem to recall the Perkins in my MF was something like 15:1 and 10:1 wasn't that rare in some gas engines. Some designs require glow plugs for starting on a cool engine and other don't. Again, my perkins didn't have glow plugs.

Combustion chamber design plays a big part in how a diesel engine operates/performs. As has been stated several times, in a gas engine speed is controlled by the amount of air entering the engine. With diesels you control fuel.

Personally think the biggest problem here in the States when it comes to diesel engines is owner resistance. With self-serve refueling being the norm, owners don't want the stinky-oily mess to get on their hand and into the car.

 

[Redneck in training]

Europe has more rational measure of polution cars produce. They measure pulution per kilometer/mile driven. US automakers lobbied government to base polution by percentage of polutants in the exhaust. Otherwise the European standard would punish large vehicles unles they were super superclean. The result is that diesels produced in Europe (by all US automakers among others) couldn't be inported until recently because they couldn't comply with US clean air standard even though they poluted much less per mile driven relative to large cars. I rent a lot of cars all over the world. When I go to Europe I always ask for diesel. Few weeks ago I rented Ford Fiesta diesel. It did about 50 mpg at normal driving.

 

[SnowRidge]

Personally think the biggest problem here in the States when it comes to diesel engines is owner resistance. With self-serve refueling being the norm, owners don't want the stinky-oily mess to get on their hand and into the car.

Right now it is the up to $1.00 a gallon price premium for diesel fuel.

The lowest differential I have seen locally is $0.60. Most stations seem to be charging $0.90 more for the stinky-oily stuff. With the average station charging just over $1.50 for regular, it definitely costs more to operate a diesel vehicle than a gasser, even factoring in the diesel's higher mileage.

 

[irvingj]

Oh, I don't know.... When diesel was up to almost $5/gal, I started tracking cost per mile for fuel-- I wanted to know if it was more economical to drive my wife's Toyta Matrix, since gasoline was so much less than diesel at the time.

Cost per mile for fuel came very close in the 2 cars, but even at the worst, the TDI was just a bit cheaper. My highest cost per mile (fuel only) for the Jetta was 11.28 cents, when diesel was $4.859/gallon. That was in July, and I must have done a lot of short-trip driving, as fuel consumption was a poor 41.15mpg on that tank. Back then, it was far cheaper to run my Yamaha Virago 750 using premium-- mileage was the same or better, but even high-test was much less than diesel.

Today I filled up the Jetta; cost was $2.799/gallon; mileage was again only 41.11 (more typical for cold weather), but fuel cost is now back down to 6.8 cents per mile. Wife's Matrix is currently getting about 24.5mpg; cost on her most recent fill-up was 8.6 cents per mile.

Although it was really hard to part with after 30 years, I'm glad I no longer have my '72 Blazer to feed!

 

[SnowRidge]

You are comparing two different vehicles. I'm talking about the buyer looking at diesel versus a gas version of the same vehicle. Most everyone in my area drives pickups, so that is what I am most familiar with. Diesel pickup sales have collapsed almost completely, even worse than gasoline powered pickups.

If you have to have a new truck with a big engine for towing, for example, it currently makes more economic sense to buy a big gasser than it does to buy a diesel. I don't think that trend is going to change, although I sure wish it would, since I already have the diesel.

 

[RobJ]

As you press down on the "gas pedal" (or raise the lever) on a diesel, you are actuating a complex bit of machinery that increases the length of the stroke of each hydraulic ram, resulting in more fuel delivered to each injector.

Actually the gas pedal on a diesel is really called a speed control. And that complex bit of machinery is a simple spring and governor weights. This setup is still used today. Instead of weights on some small diesels like mine, it's a two pronged looking spring.

This is also why diesels are so well-adapted to turbochargers, as their exhaust gas temps are considerably cooler than on a gas engine, resulting in less stress on a turbo's bearing as well as on the oil.

Pretty sure exhaust temps run higher on a diesel. This heat helps gets things movings.

 

[RobJ]

Are you saying that the flyball governor is a computer of the analog flavor?

Never thought about it in that light, it may stretch the bounds of "computer" a bit.

hehe, a bit?? Everest is a bit of a climb.

 

[RobJ]

Boy, lots of comments. Some with repeat info, others clarifying an answer from a question, etc.

One thing not mentioned so far is combustion chamber design in diesel engines. Close 3 decades ago when I was reading up on diesel engine design, there were at that time 5 combustion chamber types, each with their own operating characteristics. Some designs permit high speed (close to gas engine speeds) operation, others that permit low compression ratio's not much higher than was common 20-30 yrs ago in gas engines. I seem to recall the Perkins in my MF was something like 15:1 and 10:1 wasn't that rare in some gas engines. Some designs require glow plugs for starting on a cool engine and other don't. Again, my perkins didn't have glow plugs.

Combustion chamber design plays a big part in how a diesel engine operates/performs. As has been stated several times, in a gas engine speed is controlled by the amount of air entering the engine. With diesels you control fuel.

Personally think the biggest problem here in the States when it comes to diesel engines is owner resistance. With self-serve refueling being the norm, owners don't want the stinky-oily mess to get on their hand and into the car.

I was hoping for a primer on the 5 different types. I know of 2 basic designs. direct injection and indirect injection or pre-combustion chambers. indirect injects the fuel into secondary chanber that flows into the main chamber. this allows extra time and air movement better mix and burn the fuel more effeciantly. These are used in mines, etc. They did not have the power of a direct injection. I think they were also lower in compression...it's been a while. Combustion chambers design slightly differ, the goal is to swirl the air more to get a better fuel/air mix.

 

[john_bud]

I know my old fords just have a dead flat head with 0cc combustion chamber and then a pocket in the piston. I would like to have the spare $$ to design a set of pistons with tumble inducing topology machined into the piston to promote more thorough combustion. Ahh, the fun you can have with money.

Everest a bit of a climb? More of an evening constitutional.

Oh, I think you will find that gasoline engines have a higher potential exhaust gas temperature. From memory, I think the diesel hits about 1800F max and the gas can get to 2400F max. That's typically done by mistake with too lean of tuning and results in long term reduction in compression ratio.

jb

 

[Soundguy]

Are you saying that the flyball governor is a computer of the analog flavor?

Never thought about it in that light, it may stretch the bounds of "computer" a bit.

This kind of thought reminds me of the mechanical difference engine.. IE.. a hand-crank mechanical calculator

soundguy

 

[ccsial]

Analog computer....Yeah, I'd say so.

It processes a frequency and controls a volume. It can be programmed by a mechanical adjustment or shim. It fits the definition.

 

[irvingj]

Pre-combustion chambers... my ol' 504D had the "highly efficient Ricardo pre-combustion chamber" according to info on the beast; looked like a cross between an ear canal and a vaginal tract, but I guess it worked.... that is, until it got overheated and one of them developed a teensy crack in it.... ended up replacing the head. And then the coolant overflow jug. And then the heater core. And then the..... amazing what a little diesel compression pressure can do once it gets into the water jacket!

 

[SnowRidge]

Analog computer....Yeah, I'd say so.

It processes a frequency and controls a volume. It can be programmed by a mechanical adjustment or shim. It fits the definition.

But it doesn't.

The term computer comes from compute, which means to determine something by mathematical means. In the case of a mechanical fuel injection pump, all the computations were done by engineers during the design process. The pump itself doesn't compute anything. It is nothing more than a bit of precision machinery that operates in an entirely predetermined manner and delivers the correct amount of fuel according to the position of the throttle and the engine speed at any given moment. The amount of fuel for any given combination of RPM and throttle position having been previously computed by the engineers.

 

[N80]

But it doesn't.

Agreed. Complexity does not make something a computer. A traditional mechanical alarm clock or a stop watch can be complex, but they do not compute anything.

 

[Soundguy]

I may have to disagree.

You can have a mechaincal 'computation' due to programmed variables.

Difference engine - Wikipedia, the free encyclopedia

Furthermore, the next step up from the difference engine was the analytical engine.. which is described as a mechaincal , general purpose computer, and an importnt initial step in the history of computing.

Analytical engine - Wikipedia, the free encyclopedia

Also.. google 'castle clock'.. it was made in 1206 and is widely accepted as the first programable analog computer. Note there were mechancal calculatng devices much earlier.. like an abacus and astrolabe...

soundguy