This continuous combustion 6-cycle engine is a modification of an existing 4-cycle air cooled diesel engine. It operates on the Brayton/Joul (turbine) cycle. Air is ingested and compressed by the piston and transferred to an integral but separate insulated combustion chamber where fuel is added and combustion occurs. The expanding gases are delivered back to the piston for 2 separate power and exhaust strokes to achieve double the expansion volume. The 6 cycles are air intake, compression into the combustion chamber, expansion of half the combustion gases in the piston/cylinder assembly, exhaust, expansion of the remaining combustion gases into the piston/cylinder assembly, exhaust. Four valves are required to guide the gases.
The prototype has been started and operated on diesel, kerosene, vegetable oil, JetA, and E85. The engine has also run, but not started, on olive oil. Ignition takes place with either a spark plug or a glow plug in the insulated combustion chamber. The ignition source can be disconnected and continuous combustion takes place after a short warm up period.
This engine system has a wide flex-fuel capability. Combustion is insensitive to cetane rating, octane rating, and other special fuel needs for typical 4 cycle engines. Operation can take place even with mixtures of fuels. Fuel is combusting continuously in a high-pressure furnace. There is potential for very low emissions of HC, CO and particulates without complex after treatment systems, especially for oil type fuels. Combustion outside of the piston cylinder assembly can provide for a long time frame for combustion to take place (10x+) within the combustion chamber, compared to 4-cycle systems. Combustion is disconnected and separate from the piston movement in the cylinder. Also combustion is not sensitive to specific air/fuel ratios and can take place with excess air, helping to insure complete combustion. The basic engine construction is very similar to existing 4 cycle engine parts and geometry and could fit into the existing engine manufacturing capabilities.
A computer thermodynamic analysis performed at the University of Wisconsin-Madison showed efficiency potential in excess of a comparable diesel engine at similar compression ratios. The analysis also showed the 6-cycle system has high potential efficiency at partial throttles, which is where many engines operate the majority of the time.
At this point in the development engine rpm has been limited to 2900. The combustion chamber requires an improved insulated construction, possibly with a vacuum barrier between outer and inner wall. The timing of the valve letting combustion gases back into the piston cylinder assembly needs development. Maximum pressures are still short of those in the original diesel engine. The lower pressures and rpm have resulted in reduced power output. There is still much development to do.
Sufficiently developed, the 6-cycle engine system could be a compact, relatively simple, flex-fuel, efficient, low emission engine for use in future extended range electric vehicles.