Abstract
Research and engineering questions: Homogenous combustion is the method to pass coming EURO 6 norm without any after treatment and with a good efficiency. The main questions in this case are, how to avoid the self ignition and knock and how to control the ignition timing. The new type of 4/2 stroke engine, developed by Aumet Oy, offers new thermo dynamical possibilities to solve these problems. As the TDC temperature is possible to control separately, no self ignition occurs. As the ignition takes place always on the right side of NTC regime, no knock is possible. The way to control ignition timing in this case is SAHCCI, assisted with active radicals. Many research reports support this. The part load efficiency stays very high with this combination of methods.
Methodology: The basic questions of the Z-engine were tested with a prototype engine during two year tests in a test bench. The gas exchange and the turbulence in the cylinder was simulated and optimized with Star CD, Diesel-RK, GT-power and NSF-3 CFD simulation programs, both in steady and non-steady conditions. Chemkin was used to calculate the Livengood-Wu integral for the control of the ignition. The fuel injection with a super-cavitating nozzle was simulated with Fluent and the droplet model was calibrated with experimental data. A new evaporation model for the droplets in the special conditions in the Z-engine was created. The non-steady CFD-simulation of the gas exchange showed the importance of the understanding of the gas dynamics in this case. Also four master theses and a part of a doctor theses has been made from the Z-engine. A lot of research reports has been analysed in order to convince our self of the correctness of this project. Some of those seems to be quite unknown to the majority of researchers in this field, as the homogenous combustion has not been since a long time the main stream in the combustion research.
Results: The prototype engine confirmed the possibility to do the very rapid gas exchange and also the possibility to reach very good part load efficiency. The Diesel-RK simulation program was modified during some years to be able to perform the simulation and optimization of the Z-engine, including the integrated 4-dimensional ignition delay map for the homogenous mixture. The fuel injection to a low pressure, hot gas in the cylinder and the rapid evaporation of the small droplets was simulated .The model of the super-cavitating fuel injector was created and the results were compared with experimental date with a good match. The steady and non-steady CFD-simulations of the gas exchange of the Z-engine confirmed the small losses of the gas exchange. The exergy increase during the gas exchange at small load and at high intern EGR, gave the explanation to the very good part load efficiency. These effects has seldom been taken in account in the field of combustion engines.
Limitations of this study: As Aumet Oy is a small company, there are of course limitations of manpower and the possibility to use the other available simulation programs. As there are not so much research reports from this type of engines, a lot of literature research has been needed, because it would be not possible to Aumet Oy to do these engine tests itself. On the other hand, it is not important who makes these tests, as long the results are reliable and easy to reach as it is the case today through internet.
This paper is the most new research report from the Z-engine and it consist the results of the simulations, achieved with Diesel-RK optimization program, using 10 variables and 4 limitations in the optimization at the same time.
Conclusion: This research project show, that a new type of combustion process has been created. It is based on a new type of gas exchange and thermo dynamics in the Z-engine. Thus almost NOx- and particle free combustion is possible without knock.
Keywords: Homogenous Combustion, Emissions, Efficiency, Down Sizing, Diesel