What is the combination of air/fuel that makes diesels efficient?

 

Are you asking why diesels are more efficient than say....gas burners?? I guess this answer could explain that. A gas burner computer tries to keep it at 14.5/1 air to fuel ratio, something like the stoicheometric efficiency(if that word is even spelled right) So the gassers always trying to keep it at this point when it's idling or full blast down the highway the puter tries to keep it as close to these numbers as possible.

On the diesels, when your sitting there idling it is somewhere around 80-90/1 air fuel ratio, I have even heard someone say 100/1 at a school I attended. Then when you have your diesel loaded to the hilt, giving all she has at full fuel your diesel is still running at around a 25/1 air fuel ratio which is almost double what the gassers will do. That's why diesels are better than gassers, plus they sound cool, smell good(unless you live in Kalifornia where it has been shown that diesel fumes cause cancer in lab animals......wait a minute, why is Kalifornia of all places using animals for testing diesel fumes?? Where is PETA now????)

I hope this is what you were getting at with your question.....other than the rant about Kalifornia

 

That makes sense. You run too lean on a gasser and you burn up your valves and pistons. I heard somewhere that running lean on a diesel won't hurt it. That's why nitrous isn't as harmful to a diesel.

 

By design, a diesel is a lean-burn engine. It doesn't even have a throttle plate to restrict the airflow through the engine. This is one reason for its higher efficiency - minimal intake pumping losses (it takes power on a gasser to generate intake manifold vacuum at an idle). Other reasons are the diesel's higher expansion ratio and the higher BTU content in a gallon of diesel fuel versus a gallon of gasoline.

Rusty

 

Also diesel fuel contains more "energy" per gallon that gas. So burning an equivalent amout of diesel will provide more energy (heat) allowing you to go farther.

 

Also diesel burns rather than explodes like gas. The longer it burns the more btus it creates. That is why we have a octane rating at the pumps. The higher the number the better it burns. So with a better burn less fuel is needed. Diesel is almost akin to oil and oil does not explode but rather burns. If you were to pour a gallon of gas next to a gallon of oil and set them both aflame, the oil will burn hotter and longer than the gas. (Dont do this please!*) That is why diesel burns better because it burns hotter and longer.

I think this is what I can gather from my limited knowledge on diesels.

Jon

The author of this article is not responsible for any experiments done as a result of this article!

 

Thanks for the info everyone. What I was really wanting was to find the most efficient diesel and look into how it is designed and air fuel ratios and such.

 

Diesel fuel uses a Cetane rating, gasoline uses an Octane rating.

 

Since diesels use air on demand and not by a valve or flap (like gassers) you can't really go by air/fuel ratios. You can a little since the computer on newer ones base the amount of fuel sprayed on the amount of air consumed. It mostly depends on the effieciency of the fuel system and the computer.

 

I have just purchased a 2007 Mercedes-Benz E-320 Bluetec diesel which is claimed to have the most advanced diesel engine in the world. It is a V-6, turbocharged and develops 400 ft-lb of torque. I'm amazed at the acceleration of the car. While mine is brand new and I haven't checked the MPG consumption, many owners claim up to 42 MPG on the highway. These engines will be able to meet the environmental requirements of all the states. Incidentally, the engine is as quiet as any gasoline engine.

While in Germany to pick up my car, I saw many Smart cars which claim a 75 MPG with the diesel engine. I was told that these cars will be imported to the US in 2008.

 

Thank you Pop-Pop
I've heard the VW TDI's are getting in the 50's? The old dodge D-50s were supposed to get 45-55mpg. I don't know if the D50's were turboed?

 

I most efficient diesel I have is a 1973 John Deere 1020 3cyl. I think it's a 176 cu in. This thing will run 3 hard 8 hour days on it's 15 gal tank! Granted it's only 42HP. I have another tractor that will burn 15 gallons in an afternoon.

 

John Deere does have some efficent tractors. Kabota has some too. Is that JD turbo charged?

 

It's not directly because of the combination or ratio that makes diesels more efficient than gas engines. While it is true that the ratio of the amount of air to the amount of fuel is very high, the two are not mixed at that ratio for combustion. So, the important information is that there is always an excess of air available. As the injection happens the mixture right at the nozzle is very rich and the mixture out near the cylinder wall is very lean. The fuel burns at the ratio that works best and burns completely beause there is more air than needed for the amount of fuel. This is always true except at full power.

Diesels are more efficient because there is more energy in the fuel and they don't have to maintain a high vacuum in the intake system. Gas engines with caburetors are almost always operating at a less than optimal fuel/air ratio and diesels are always burning their fuel completely (except at maximum load).

Wetspirit

 

http://world.honda.com/news/2004/4040506.html

Check this out in testing it was getting 92 MPG and set a ton of speed records to boot. Thus at 92 MPG I am sure the EPA would never allow it into the US at these specs.