why do diesel engines obtain good gas mileage?

Answer 1

higher compression + fuel burns more completely

Answer 2

Three reasons,

The higher compression ratio and direct injection gives the diesel more efficient combustion.

The lower engine speeds possible with a diesel have considerably less friction losses compared to the speeds needed (rpm) for a gasoline engine.

There are less pumping losses because a diesel does not have a throttle (the intake is wide open at all times) and does not have to maintain a vacuum in the manifold.

Answer 3

Diesel engines don't have to be spun over 2,000 rpm to make all their horsepower. They have tremendous torque. The lower rpm saves fuel. Average RPM over the road is 1,200 RPM. The motors last forever. The entire fuel injection system is bathed in very light fuel oil / kerosene mix. So are the combustion chambers, rings and pistons constantly being lubricated up top of the pistons. Compression ratios up to 22:1 because high quality fuel oil / kerosene mix has a very high cetane rating, The higher the cetane rating the slower the fuel burns and the better efficiency of the engine.

Answer 4

All the answers are close, but not completely correct.

Diesels achieve better fuel mileage because almost all of them have longer crankshaft strokes than their gasoline counterparts. this longer stroke gives the crankshaft more leverage and the ability to drive the drive-train and push the car down the road easier.

Why does this give you better fuel economy? because a longer lever takes less energy to move than a shorter lever does. the same thing applies in engines.. engines with a longer stroke can move heavy vehicles and heavy loads easier and with using less fuel than engines with short strokes.

You may be asking yourself then, "why doesn't every engine have a longer stroke then?" This is because by lengthening the stroke, you also increase the time it takes for the crankshaft to make a full circle. a shorter stroke can make the circle faster and is therefor capable of more engine RPMs where as the longer stroke engines are limited to less rpms and horsepower capabilities.

things like higher compression do help the diesel engine get better fuel economy, but is not the sole reason they are superior when it comes to fuel economy, torque, and pulling heavy loads.

Answer 5

Does it really compared to price of the fuel and the size of the engine, not to mention the distance you have to drive to find diesel fuel. In my area, I have to drive almost 10 miles to a gas station that has diesel, compared to 7/10 mile that has gas. If it is so much more efficient, why arent all cars diesel in such a green moving world?

Answer 6

Diesel engines have a higher compression ratio. Also, liquid diesel fuel is significantly denser than liquid gasoline. When this is taken into account, diesel fuel has a higher energy per gallon.

Answer 7

Fuel burns completely, higher compression more power can be extracted and Diesel fuel has more BTUs than Gasoline.

Answer 8

thats because diesel is more efficeint than gas. diesel engine tends to have higher compression ratios than gas engines

Answer 9

all the tollerances are closer and everything fits tighter less slop in the engine

Answer 10

the simple answer is higher thermal efficiency