Velozeta Six-Stroke Engine

Six stroke engines add another two piston motions to each fuel injection cycle to those of the common four stroke engines. Everyday cars and trucks use four stroke engines. These are called four stroke because for each time that a new shot of fuel is burnt, the pistons sweep up twice and down twice, for a total of 4 sweeps or strokes. The four stroke sequence goes like this:

Intake Stroke

This stroke begins with the piston at the top of the cylinder. The piston moves down, opening up space in the cylinder. As it does so, the valves in the head above open and fuel-air mixture gets sucked into the cylinder.

Compression Stroke

When the piston reaches the bottom of the cylinder, the valves close off. As the piston rises up the cylinder, it compresses the fuel air mixture, which now has nowhere to go. This compression primes the mixture for detonation. The stroke ends with the piston at the top of the cylinder and the mixture compressed into the small space in the head above.

Power Stroke

Now the fuel air mixture is detonated by the spark plug. The resulting explosion forces the piston down the cylinder and rotates the crankshaft against any attached load.

Exhaust Stroke

Exhaust valves in the heads above open up, and the piston rises up the cylinder, forcing out the exhaust gases, which are the ashes resulting from the combustion of the fuel air mixture.

Students from the College of Engineering at Trivandrum in India have developed an engine which adds two more strokes after the exhaust stroke. It uses air to scavenge heat from the cylinder and convert it to motive power. This can improve efficiency, because normally that heat is just wasted. The engine is a modified Honda four-stroke engine. After the exhaust stroke, valves open and allow cool air to flow in as the piston descends. The air gains heat from the very hot cylinder which causes it to expand. This heat-driven expansion occurs forcefully enough to actually power the piston down. In other words, there is a secondary, weaker power stroke after the exhaust stroke. On the sixth stroke (which is a secondary exhaust stroke), the rising piston forces the now warmer air out the exhaust.

This engine uses 40% less fuel and can run on normal gasoline.