Diesel, the word brings visions of 100 car trains chugging across the landscape or semi-trailers climbing a grade. Why have diesel engines become the go-to solution for prime power production? The “prime mover” is the technical term used in science and engineering and refers to any machine that converts energy from a source energy to mechanical energy. Compression ignition, spark ignition engines, electric motors and steam engines are prime movers. But why the emphasis on the diesel, or compression ignition engine.
Rudolf Diesel Engine
Rudolf Diesel is credited with the invention of the diesel engine and his work with MAN AG from 1893 to 1897. The thermodynamic efficiency of the diesel is what sets it aside. During this period the steam engine rained supreme. But 90% of the fuel’s energy was wasted in steam engines.
Diesel Engine Compression Ratio
Compression ratio, the difference in volume when the piston is at the bottom and the volume at the top of stroke is a governing force as to the efficiency of an internal combustion engine. The higher the compression ratio the more efficient the conversion of chemical energy to heat, and heat and expanding gases are what drive the piston. In spark engines the fuel and air are mixed before entering the cylinder of the engine. High compression ratio lead to pre-ignition or engine ‘knock’ that can blow out the top of pistons and cause other damage. The pre-ignition is set off by higher compression ratios, thus we have high octane but expensive fuels that resist pre-ignition. But even the 110 octane of aircraft engines can only handle up around 12:1 or 13:1 compression ratio. The diesel engine use timed high pressure fuel injectors directly in the combustion chamber to inject fuel under pressures that cause it to ‘mist’ or break up into tiny drops of fuel that are ignited by the heat of compression inside the combustion chamber. The finer the mist the more efficient the processes. Because of the compression ignition that puts additional stress on engine components diesel engines are built more robustly than spark ignition engines, and are therefore more reliable and generally last much longer. The higher compression ratio makes diesels more thermodynamically efficient. Diesel engines utilize compression ratio from about 15:1 to as high as 23:1 improving the chemical to mechanical energy efficiency.
Diesel VS Gasoline Fuel
Diesel fuel is denser than gasoline. A gallon of diesel weighs more than a gallon of diesel. Consumers either corporate (meaning any business) or private are delivered their fuels by volume. In the US gallon, internationally liters. But large-scale users like aircraft and ships measure consumption by the mass uses. Pounds or kilograms. Being denser there is more bang per gallon with diesel than gas engines.
Function of Turbocharger in Diesel Engine
Turbocharging is common with diesels. Utilizing the waste heat in the exhaust to turn the turbocharger makes the diesel even more efficient as your trapping and using energy that would otherwise be lost up the exhaust stack.
Compression ignition engines appears the way to go. But not everything is free. Diesel has a dark side as well. Diesel fuels tend to have a high sulfur content. The combustion produces the sulfur-based pollutants and nitrous oxide (NOx). Any smoke from diesels indicate incomplete combustion, and to some the odor of a running diesel is obnoxious. In the US sulfur content has been restricted with the current low-sulfur fuels there is much less concern over sulfur in diesel fuel. Diesel particulate matter (DPM) or diesel exhaust particles (DEM) i.e. smoke is reduced by pre-combustion chamber and higher heat to ensure full combustion of the fuel, but exhaust filters are used to trap what is left. The modern diesel engine is very efficient, reliable and conforms to low pollutant emissions specified in the Tier 4 Final standard that all new manufactured engines must comply with. Some emissions controls that are used are selective catalytic reduction, exhaust gas recirculation and Diesel Exhaust Fluid (DEF). The downside is that diesel has become a mixed soup of additives that causes diesel to break down in long term storage, but there are technics to renew its properties.
Clean Diesel Generators for Sale, Rental & Leasing
Overall, the diesel engine is the most thermodynamically efficient solution for a ‘prime mover’. It is used to power trucks, trains and ships. About the only application that is not suitable for diesel implementation is aviation. The diesel is chosen to power our generators and they comply with all EPA standards. Environmental Power Solutions offers clean diesel generators for sale, rental and leasing. Contact us to learn more today!