Abstract
Aumet Oy has developed a new type of combustion process, the Z-process. It differs more from the actual combustion engine processes than any of those have differed from the previous ones.
The Z-process is a mixture of the 2-stroke and the 4-stroke processes. Like in the 4-stroke process, the exhaust gases exit the cylinder through the exit valves and the incoming gas enters through the intake valves into the cylinder. Like in the 4-stroke engine, the piston removes the exhaust gases from the cylinder in the Z-process. The gas exchange occurs at every crankshaft rotation, like in the 2-stroke engine, but totally differently. The gas exchange occurs during a very small crank angle, close at the top dead centre, while it occurs close at the bottom dead centre in the 2-stroke engine. The gas exchange pressure is very high in the Z-process, typically 15 25 bar, while in the 2-stroke engines it is typically 1,5 2 bar. The Z-engine, working according to the Z-process, produces work at every rotation of the crankshaft, like the 2-stroke engine. The geometrical compression ration of the Z-engine is high, typically 50 and the expansion ration is typically 20 30, while it is 7 - 10 in the 4-stroke engines. The high expansion ration is possible, because of the control of the temperature of the pre compressed gas. After the gas exchange, there is a secondary compression in the working cylinder in the Z-engine. During this period the pressure of the gas rises typically to 160 bar, but its temperature stays at reasonable low level an it is adjustable. The high pressure of the incoming scavenging gas causes a rapid swirl, the swirl number is typically 30 40 and it can be adjusted. In the Z-engine the combustion space (swirl chamber) is in the piston crown and this enables the tangential injection with a conical single hole nozzle using only 500 bar pressure. The out coming fuel stream is a tube, dia typically 3 mm and the wall thickness only 0,03 mm (like CAV Microjector). Thus it is easy to realize HCCI-combustion in the Z-engine, as the size of the drops is very small. Also a controlled continuous burning is possible, making it possible to control the ROHR (rate of heat release), without NOx or particulate emissions.
The advantages of the Z-process are: low NOx level, low particle level, high efficiency, especially at part load and the HCCI and or continuous combustion. The Z-engine can be constructed for example as a 2-cylinder opposite piston engine or as a 2-cylinder in-line engine, with separate or integrated compressor part and with or without turbo or supercharger. For more information: see www.aumet.fi