Excellent article from NY Green Transportation Examiner Nick Prague
If we go back 100 years we would find a wide assortment of propulsion systems used on cars. We had electric cars, along with street outlets in cities to charge them. We even had steam powered cars. All of these different propulsion systems were pushed aside and gasoline and diesel piston engines became the engines of choice. This dominance occurred for the simple reason that these engines were the most reliable at the lowest cost.
Diesel engines in particular are remarkable power plants. They have been made in both two stroke and four stroke designs, and in fact your PT boats and tanks of World War Two were powered by two stroke diesels for their sheer reliability. They are fuel efficient, and the oily nature of diesel fuel contributes to a very long engine life.
Once emissions became an issue, the diesel engine came under very tough scrutiny. Two stroke diesels were dirty engines by their simple design and have just about been eliminated from production. While it looked for awhile like the diesel was heading towards extinction, technology has emerged to clean the emissions from four stroke diesels so that the diesel has been resurrected as a viable power plant for a cleaner, greener world.
A diesel gets good fuel economy because of its high compression design. Simply stated, if you raise engine compression you increase fuel economy. The use of unleaded fuel forced a reduction in gasoline engine compression, but diesels are high compression engines by their basic design. High compression squeezes more useable energy out of the fuel. Modern small diesel engines are now getting better mileage than hybrids. It also results in a high combustion temperature that helps to reduce hydrocarbon and carbon monoxide emissions.
Diesel engine emissions were an issue in two areas. First, the high combustion temperature resulted in high levels of Oxides of Nitrogen emissions, and most importantly diesels had a high level of soot emissions. Modern emission controls have cured these issues so that the modern diesel is a very clean running engine. The tailpipe in the picture is on a diesel engine in a transit coach with 60,000 miles, and remains as clean as it was when new.
Now that emissions have been corrected, the diesel engine becomes one of our better green solutions at the current time. A small diesel engine has lots of torque, making for a car that performs well. The use of a small engine enhances the clean design since a smaller engine, everything else being equal, breathes less and naturally pollutes less. In addition, since diesel engines last longer they will remain clean burning for a longer time than a gasoline engine.
Acceptance of diesel cars in the United States has been poor, primarily because the average motorist is not sensitive to the different nature of the power train. Diesel engines develop more torque than gasoline engines, but they don’t rev like gasoline engines. They also must be warmed up in cold weather, and maintenance intervals must be more closely followed. Oil changes and filters are critical to the reliability of a diesel.
The motorist who considers these differences and works with his machine will be rewarded with a car than can realistically get 60 miles per gallon for several hundred thousand miles. Maybe its time for Americans to rediscover this old, proven engine, but don't treat them like gasoline engines.