HisDivineShadow

How effective is the burning of fuel say in a V8 like mine? If I remember correctly most internal combustion cars that run on gas are maybe 25% to 30% effective, anyone here have some specific numbers for engines like the ones in our cars?

Vader

Divine,

There are different kinds of "efficiency" as it relates to a piston engine. Thermal efficiency, mechanical efficiency, and volumetric efficiency.

Thermal efficiency is the net amount energy taken from the combustion process that is converted to power output, or work. A typical low compression engine has a thermal efficiency of about 26%. In a higher performance engine, thermal efficiency can reach as high as 35%.

Mechanical efficiency is the net energy transmitted from the combustion process to power output, or work, after correcting for mechanical inefficiencies, like friction and design compromises. The typical piston engine has about 94-95% mechanical efficiency.

Calcuolated together, in a relatively common stock engine, only about 20% of the power available from actual fuel combustion is converted to output power, or work. You can subtract even more from that result for drive line inefficiencies.

Volumetric efficiency is the ratio of the theoretical volume of air and fuel that can be drawn into a cylinder based on it's volume compared to the aactual volume of air and fuel that is drawn into the cylinder under normal atmospheric pressure. Typical naturally aspirated engines "enjoy" a VE of around 75-80%, if they are well-designed.

Was that sufficiently confusing?

HisDivineShadow

Yeah, just the kind of stuff I wanted, thanks

Vader

Wow. You're just as deranged as I am...