Did you know that diesel fuel economy is much better than the fuel economy achieved by most gasoline engines? Most people aren't aware of this fact. They see buses and large trucks belching out dark black smoke and assume that the only reason diesel engines are used at all is because of the greater torque that they generate, which allows them to pull much heavier loads than gasoline engines of comparable sizes. And they're wrong.
A BRIEF BACKGROUND ON THE DIESEL ENGINE
The diesel engine was created by Rudolf Diesel in 1893; he patented the designs in 1894 and 1895 and called it a slow-combustion engine. The diesel engine is known as a compression-ignition engine. What this means is that the engine sucks in air, compresses it to raise its temperature, and slowly introduces the fuel to the heated and compressed air. The heat of the air causes the fuel in the air to combust. There is sufficient resistance to the expansion of the combustion gases to keep the internal temperatures at manageable levels.
DIESEL FUEL ECONOMY OUTWEIGHS GASOLINE BY AS MUCH AS 40%
The MAN S80ME-C7 low speed diesel engine is one of the most fuel efficient engines of its size on the planet. It is a diesel engine that uses only 155 grams of fuel per kWh of energy produced. This gives it an energy-conversion efficiency of 54.4%. A fuel efficient turbodiesel engine that is running properly can deliver as much as 30 to 35% greater economy than gasoline-powered engines of comparable size. One of the reasons for this increased diesel fuel economy is the fact that diesel fuel is denser than gasoline, although it does have a slightly lower calorific content. Something else that comes into play is that diesel engines don't have a butterfly valve in the inlet system to close of the air supply.
IMPROVEMENTS IN TECHNOLOGY HAVE INCREASED FUEL ECONOMY OF DIESEL ENGINES
Technological improvements have helped both diesel and gasoline powered engines increase the fuel economy they're capable of. Better injectors have helped, however most likely the single technological advancement that's provided the greatest increase in economy is the electronically-controlled injection system.
By monitoring a variety of engine performance parameters (e.g. engine speed, load, and temperature), the computer that controls the fuel injection is able to determine and inject exactly what the engine needs to achieve the best possible performance and economy.
With these improvements, a truck such as the GMC Sierra 3500 HD heavy duty pickup, with its 6.6-liter Duramax Diesel engine, can develop 785 foot-pounds of torque and can go up to 680 miles on a single fill-up of its 38-gallon tank. This is an impressive 17.9 miles per gallon.