We are comparing the difference between external combustion engines (steam engines or turbines) to internal combustion engines using gasoline or diesel engines on diesel and other fuels. We left off part one discussing air-fuel ratios (AFR) and are now considering another metric used in comparing fuels and engines.
Brake Specific Fuel Consumption
Another metric used to compare power production is the “Brake-Specific Fuel Consumption“. First gasoline weighs in at about 6.1 lbs. per gallon. Diesel is 7.2 lbs. per gallon (higher density). A four-stroke in tune gasoline engine will consume about a ½ gallon of fuel per hour for each unit of horsepower. A hundred horsepower engine will burn 50 lbs. of fuel hour, or approximately 8.2 gallons. Double the horsepower double your fuel consumption. For diesels it is between 0.380 to 0.450 lbs./hp/hour. Diesels are bit harder to clarify because of the numerous rolls’ diesels may perform. From stationary or marine large-scale diesels to mobile units in a pickup or car and least we heavy construction equipment, heavy equipment and small trucks are the most variable. Few diesels run for long periods at their rated power, in fact the sweet spot on fuel efficiency seems to be about 70% of the rated power output. Remember power production is related to compression ratios and diesels have the highest ratios in use, more power per weight of fuel. But wait, the power production substations dotted around the valley to assist power production during peak demand are diesel, i.e. reciprocating internal combustion compression ignition engine. What does this entail in power production on smaller scales? It is difficult with current technology to improve on the diesel-powered electric generator for small scale or mobile electrical power production. Hence the diesel-electric system used by railroad engines and some marine applications.
Diesel Electric Generators
The diesel-electric generators are effective because the needed scale is smaller. To be effective the external combustion steam turbine needs large scale machinery to reach the most efficient use of the system to make power. Substation diesels may start up on diesel but then switch to natural gas to run. Diesel produces the most power per volume, but natural gas is cheaper. As the load increases the ratio of diesel to gas is raised. For mobile power generation over 100 kW the diesel is king, as it produces the most economical prime mover solution to electrical power generation. High volume compressors on jobsites also incorporate diesel engines. Diesels are the most thermodynamic and fuel-efficient solution to date for small scale power production. Another observation is that diesels are becoming the prime propulsion solution in the marine environment with large scale engines. Even large applications like container ships and tankers are driven by 9-foot-tall 18-foot-long diesel engines.
Clean Diesel Generators for Rent, Lease & Sale
It’s hard to beat the compression ignition or diesel engine as a prime mover for multiple applications. Because so many applications use diesels it ensures that a fuel marginalized 50 years ago now finds usage outpacing the supply, the 30-40 cents per gallon over regular gasoline prices for diesel is implicit. Call Environmental Power Solutions to learn more about our clean diesel generators today.