Reciprocating steam engines are only about 20% efficient capturing only a fifth of the heat energy and converting it to mechanical energy. Most internal combustion engines are closer to 40-60% (modern tech) so why are we not using diesel engines (most efficient internal combustion engine) for ‘bulk’ electrical power generation?
Reciprocating Steam Engines
First, note the term Reciprocating Steam engines. Modern steam energy plants and marine applications do not incorporate reciprocating (linear motion converted to rotational motion) they use the modern steam turbine. These turbines are built to capture the heat energy and lowering pressures by progressively larger vane area that converts the heat in steam to rotational energy. Up to 80% of the heat energy is extracted and converted to mechanical energy to drive massive generators for power production. The big advantage is that there is an inherent flexibility for fuels because these are external combustion engines that use water heated to steam in remote boilers. The flexibility in fuels allows the use of natural gas, coal, oil and biomass that is combusted to provide the heat to boil the water.
Natural Gas Fuel
Because of environmental considerations all new plants are turning to natural gas for fuel or converting coal burners to natural gas. Petroleum based products are expensive, but there is a finite amount of natural gas available to be used in power generation. The power companies compete with the household consumer for the available sources of natural gas affecting the price of this resource.
Steam turbine plants are large scale implementations not adaptable to mobile land or air platforms. Aero technology dictates low power plant weight and higher output to total airframe weight. In other words more power for less weight. Jets are gas turbines and are the most efficient way to provide thrust as well as turbine engines that turn propellers. Indeed, virtually every successful modern rotary wing aircraft (helicopters) use gas turbines as the prime mover of the craft. High power for low engine weight, but at the cost of lower fuel efficiency.
Attempts at harnessing steam turbines for rail usage have not produced acceptable results, which brings to the next topic – internal combustion engines.
How Does an Internal Combustion Engine Work?
Take the nitromethane fueled dragster, an internal combustion engine of about 500 cu. inches displacement (8.2 liter) engine producing between 8,500 to 10,000 horsepower. The engines and clutch systems on the fire breathing monster self-destruct with only one pass down the quarter mile, 5 seconds of heart pounding heat and noise that turns thousands of dollars of engine and clutches to junk. How? Gasoline burns at a theoretical 14.7 to one ratio based on mass or weight (mass in a gravity field, like earth). That translates to 14.7 pounds of air to 1 pound of fuel. Diesel needs Stoichiometric (a chemically complete combustion event. AFR (air/fuel ratio) to produce of a 14.5:1 ratio. The active component of air is oxygen and makes up about 20.95% or our atmosphere. Alcohol contains oxygen and needs an AFR of 6.4:1 while nitromethane is 1.7:1 AFR (Lots of Ox in the nitromethane molecule). About a 2 to 1 ratio. Fuel (nitro or nitromethane) makes for dramatic horsepower numbers because the mass or weight burned per second by the engine. More fuel weight per cycle more power. And the reason you get less mileage per gallon with alcohol is at the 6.1 to 1 ration, less fuel to air. As a side note, your sedan puts out about 250 to 300 horsepower. The supercharger on a top fuel dragster or funny car absorbs about the same amount of power as your street ride.