Diesel engine
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DETAILS/DESCRIPTION:
Diesel* is credited with the invention of the diesel engine and he produced the first successful diesel engine at Augsburg in Germany in 1897. It was based on the idea of using compression to supply heat. Inspired by Carnot’s* theory of the ideal heat engine, Diesel aimed to produce combustion at a constant pressure and get the maximum amount of work out of the heat energy.
The diesel cycle:- air in the combustion chamber is subjected to compression which rapidly brings it to a very high temperature (higher than the ignition point of the fuel). Fuel is then injected into the combustion chamber. The heat of the compressed air causes the fuel to self-ignite and the expansion of the hot gases released drives the piston.
The diesel engine differs from the internal combustion engines like the gasoline engine where the fuel and air are mixed before entering the combustion chamber, lightly compressed, and then ignited by a spark. Because Diesel believed that maintaining a constant pressure was critical to the thermal efficiency of his engine he wanted to burn the fuel during the first part of the downward stroke of the piston very slowly so that there would be no pressure rise.
The fuel was therefore sprayed gradually into the hot air in the combustion chamber, beginning at the moment when the piston was just at the start of its downward movement. Diesel’s mistaken belief in the importance of maintaining a constant pressure was eventually abandoned, and today fuel is injected into the combustion chamber near the end of the piston’s downward stroke and burns rapidly with a sharply rising pressure.
In the first diesel engines, fuel was injected into the combustion chamber by a compressed-air jet. This caused problems and after 1910 mechanical injection was adopted. The first diesel engines were amazingly energy efficient and were low in fuel consumption but they were large and heavy, and the precision necessary for the fuel injection process made them expensive.
They were used only as stationary engines but after the first marine installation in 1910 their use in this area took off and during World War I they were the primary energy source for submarines. At this time the American electrical engineer Sperry* developed a mechanical injection system for this diesel engine.
By the 1920’s small cars with diesel engines were produced and this opened up the application of the diesel engine for use in vehicles such as locomotives, trucks, tractors and buses where the high reliability of the diesel, its long life and relatively low servicing needs are important. In 1928 the International Harvester Company installed its first four-cylinder diesel engine in a tractor. They were followed by Caterpillar Tractor who in 1932 attached a diesel engine to a “twelve bottom gang plow” for a demonstration on a ranch in Oregon. The plough ran continuously for 46 days during which it traveled 3,500 miles and ploughed 6,880 acres at an average fuel cost of less than six cents an acre.
The combustion process and fuel injection system of the diesel allows it to use unrefined fuels. Low grade fuels can be burned at a comparatively low rate of consumption per horsepower per hour. Gasoline with same airflow rate will produce much more power, so when diesel is used to produce the same amount of power as gasoline, the result is a much heavier and larger engine. The largest engines are used in electricity generators and for propelling ships where the weight and bulkiness of the engine is not a factor. Apart from a higher initial cost of purchase, the disadvantages are those of smell, noise, vibration and emission of pollutants.
ONELINER: Diesel engine
OTHER CONNECTIONS: None
BIBLIOGRAPHY:
Nitske, W Robert and Wilson, Charles Morrow, Rudolf Diesel, University of Oklahoma Press, Norman, Oklahoma, 1964.
Moon, John F, Rudolf Diesel and the Diesel Engine, Priory Press Ltd., London, 1974.