Abstract
Keywords - efficiency, emissions, diesel engine, combustion
From 1990 to 2000 many car manufacturers and research companies searched for ways of improving the 2-stroke car diesel engine. The aim was to produce a lighter, smaller and more economical engine. Some remaining problems, such as HC emissions and excessive piston ring wear, prevented the introduction of the 2-stroke diesel engines in modern road vehicles.
In 1999, Aumet Oy began to research a 2-stroke car diesel engine, called the Z engine, in cooperation with the Internal Combustion Engine Laboratory at the Helsinki University of Technology (HUT) and the Energy Technology Department at the Lappeenranta University of Technology (LUT). So far, three master´s theses, two SAE Papers and one Fisita Paper have been completed on the subject. Modern simulation tools, such as Star CD, GT-Power and Diesel RK have been used . Aumet´s research project was a part of the Finnish Engine Technology Programme, ProMotor, and it was supported by the National Technology Agency Finland, TEKES. A prototype engine made its first start in December 2003 and the testing of the engine has been made three years in a test bench at VTT (Technical Research Centre of Finland). The Z engine has got until now five international patents, several are pending and Euro patent is expected to get before summer 2008.
The Z engine introduces a completely new work cycle. It combines the best parts of 2- and 4- stroke engines. In the Z engine, work is produced at every crankshaft revolution as in 2-stroke engines. The Z engine does not have 2-stroke type scavenging or its disadvantages: mixing of the new charge with the exhaust gas or the loss of the scavenging gas to the exhaust channel. The Z engine uses poppet valves, so there are no problems with the wear of the piston rings and the emissions caused by lubricants. Thus, it is possible to halve the number of the working cylinders of the engine by having one integrated compressor cylinder in the engine. In engines, size of car engines, the piston compressor has a better efficiency than rotating blowers, for example Roots blower and it is also more economical to produce. The turbocharger lowers the volume of the compressor cylinder by 50-70%. A 2-cylinder Z engine is equal to a 4-cylinder 4-stroke engine in its power output and balancing.
In the Z engine, it is possible to utilize the combined high swirl Z combustion with a controlled homogenous charge compression ignition combustion (HCCI). The Z engine has the potential to comply with future environmental legislation without expensive exhaust gas after-treatment.
By using the Z engine it is possible to reduce the manufacturing costs of the vehicles. All the components used in the Z engine are like those used in normal engines and compressors. For this reason, there is no need for many changes in the component supply chain. It is possible to have a diesel car without a NOx catalyst, when using the Z engine.