At UC Berkeley last year I built a rig to accurately measure the combustion efficiencies of a piston IC engine to see what the real eff. numbers are. We used ethanol for a fuel source and squirted a small amount of if (200 proof bourbon) into the combustion chamber. The rig has a small piston with a seal that prevents any energy from escaping around the piston so it seals completely.

The rig consists of a clear plastic tube, a pressure sensor, a piston and a computer. The computer records the pressure and a high speed camera @1000 FPS measures the piston position in the tube after ignition.

The silver piston reaches the top of it’s travel in 0.033 seconds or about 60 feet per second. The piston then returns to it’s starting position after all of the energy from the fuel is expended.

We found that ethanol has a maximum efficiency of 29%. Gasoline roughly the same.

This means that from the gas tank to powering the car is at most around ~30% eff.. Tesla EV is about 90% efficiency. That’s the advantage.

We then proceeded to fire these 3D printed mortar rounds out in the parking lot for fun ?