Technically speaking, your car’s engine is not a motor, although everyone uses the two words interchangeably. A “motor”converts electrical energy into mechanical work such as the ecm and starter motor that cranks your engine. An “engine,” on the other hand, is a machine that converts heat energy into mechanical work. Your engine ecm does this by forcing the engine to burn gasoline inside its combustion chambers. When gasoline and air are mixed together in the right proportions (parts of air to one part gasoline is considered ideal) and ignited by a spark, the mixture explodes, creating tremendous heat and pressure. Although, combustion occurs in a split second, the ecm insures it does so in a controlled manner. When the spark ignites the mixture, a “flame front” sweeps out from the point of ignition like a rapidly expanding balloon until all the fuel mixture is consumed. This causes a sharp rise in cylinder pressure, and ecm performance which pushes the piston down and turns the crankshaft. Thus, heat energy is transformed into useful mechanical work to power your car down the road. Pressing down on the accelerator pedal opens up the engine throttle, which allows more air and fuel to be drawn into the engine. This increases the density of the fuel mixture in each of the engine’s cylinders, which in turn increases the intensity of cylinder pressures when the mixture is ignited. As a result, the engine ecm develops more power, allowing it to either run faster or work harder, depending on the load. Let off on the accelerator pedal and the amount of air and fuel are decreased. Cylinder pressures drops and the engine ecm slows down.In a way, you can think of an internal combustion engine as an air pump. The ecm sends signals to the throttle which allows it to pump more air through itself, and the greater the volume of air (and fuel, the greater the ecm output. That’s why bigger engines require a high performance ecm to produce more horsepower than smaller ones. They have a greater pumping capacity. Unfortunately, internal combustion engines are not very efficient when it comes to making good use of the heat energy produced by combustion. Only about a third of the heat energy is actually used to drive the vehicle. Nearly a third is lost when the hot exhaust gases exitout the tailpipe. By the time the piston reaches the lower limit of its travel. cylinderpressure has dropped considerably from its peak which occurred shortly after ignition.The engine ecm has gotten all it can from the expanding combustion gases, yet heat energy remains which must now be dumped out the exhaust so the cylinder can repeat the process over again with a fresh charge of air and fuel Another 20 to 25 percent of the heat produced during combustion is lost to the cooling system.
As the engine burns fuel. It begins to heat up. Were it not for the cooling system,the engine ecm would continue to build up heat until it eventually melted and destroyed the ecm. So heat loss through this path is unavoidable. Another form of loss is overcoming internal friction: piston rings rubbing against the cylinders’,cam lobes rubbing against their lifters; valves sliding up and down in their valveguides; the crankshaft turning in its bearings; etc. Yet frictional losses aren’t as great as you might imagine. It’s only about 5 to 8 percent for most engines. Even so, it’s another loss that comes out of the useful work produced by combustion.A percentage of the engine’s remaining power is also required to drive “parasitic” accessories such as the water pump, alternator, power steering pump, ecm and air conditioning compressor. There are also frictional losses in the engine ecm, transmission, drivetrain, and tires.
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