There exists a definite bias in this forum for diesel powered generators. As we specialize in mobile trailer mounted industrial size generators, the diesel is the only viable power unit for these units in the field.
Compression ignition engines have a compression ratio of 14:1 up 25:1, this is the mechanical ratio of the swept volume of the cylinder by the piston, and the remaining volume in the combustion chamber. Generally, the higher the compression ratio on an engine the more efficient it operates. Since the diesel is a high compression engine, using the compression of the atmospheric gases and injection of fuel into the combustion chamber to ignite the fuel-air mixture conversion of the chemical energy to heat and the expansion of gases to push the piston on the power stroke makes the diesel more efficient. Because of the limitations of the spark ignited gasoline engine and that the induced mixture is a combination of air and fuel, compression is limited to about 12:1 in practical street driven applications, though competitive motor sports may push this restriction, but require special fuels.
Diesel VS Gasoline Engine Generators
Starting the typical diesel engine incorporates glow plugs, creating an electrically powered hot spot to start the engine. Another feature is turbocharging. Using the exhaust gases to power a compressor that introduces air into cylinders at higher pressure. Using waste heat from the exhaust improves the efficiency of the engine.
Compression ignition puts a lot of stress on engine components, so manufacturers tend to build very robust diesel engines. This makes a diesel much more reliable and rugged than their spark ignited cousins. Diesels tend to experience lower maintenance costs as well. A liquid cooled diesel will go from 12,000 to 30.000 hours before major maintenance is required versus the 6,000 to 10,000 hours for a gasoline engine. Gasoline engines burn hotter and therefore have relatively shorter life spans than diesel engines. This cooler running extends the life of the engine but makes it more important to add accessories like engine block heaters and oil heaters, as these engines warm up slower.
Generator Fuel Consumption
Fuels in the US and the world generally are sold by the volume not weight. But performance is based on weight of fuel burned in a specific time frame, usually seconds. Diesel is denser than gasoline, in effect a gallon of diesel weighs more than gasoline, delivering more energy per volume. Another detail is volatility. Volatility is the rate and temperature of evaporation. As fuels need to be vaporized to burn the low volatility of diesel versus gasoline, improves fire safety. Because of the fuel and mechanical efficiency of diesels fuel cost per kilowatt is 30 to 50 percent lower than gasoline powered units.
Generator Efficiency & Costs
The scale of the power requirement sets the demarcation between gasoline and diesel. Because of their construction diesel engines tend to have higher up-front costs, making them somewhat impracticable in small light generators up to 15 kW. This is the area dominated by gasoline gensets (engine-generator sets) or fueled by the gases, natural and propane. A case can be made about home standby gensets running spark ignition engines powered by natural gas. But this is usually not an option for mobile gensets. Diesel represents the safest, most cost-effective solution for many generator applications. Most electrical substations depend on diesel units to power-up and support the grid during high demand hours. With hybrid units that start on diesel and run on natural gas there is a blending of technologies, but high-power demand will change the fuel ratios to more diesel fuel as the chemical energy is denser producing more power. As the natural gas mixture is increased, these units tend to be derated to lower power output.
Clean Powered Diesel Generators
The efficiency of the diesel engine is one reasons it dominates as the power source driving the railroad and trucking industries. There is a definite advantage to mobile and stationary dependency on the diesel engine as the prime mover of choice. Environmental Power Solutions offers clean running diesel generators for lease, rent and sale. Contact us to learn more!