The most common car engine is a 4-cylinder 4-stroke engine. The car manufacturers have a great pressure to lower the cost of the cars and this deal also with the engines. The challenges are the coming new emission norms (for example EURO-6) and also the customer acceptance, because of the fact, that the car drives are used to the 4-cylinder engine and they want to have the same driving fun also from the new engines One of the latest development in 2-stoke engines is the Z-engine (1), having the compression partially transferred outside of the working cylinders. This offers new thermo dynamical possibilities to adjust the working cycle and the combustion. As there are methods to control the temperature at TDC, a HCCI-combustion is possible in the Z-engine at all loads. This lowers significantly the cost of the engine, as no urea injection, or NOx catalyst is needed to pass the coming EU-6 emission norm. The cost of the Z-engine is lower also because of the fact that it has only 2 working cylinders instead of 4. So far, four master's theses, four SAE Papers (71, 72) and four Fisita Papers have been completed on the subject. Modern simulation tools, such as Star CD, GT-Power, Diesel RK, Fluent and Chemkin have been used. The prototype engine made its first start in December 2004 and testing of the engine has been made two years in a test bench. In the HCCI combustion simulation of the Z-engine, a 4-dimensional ignition delay map, calculated with Chemkin and integrated in Diesel RK (74), has been used. The simulations and tests (1) with the test engine show that the Z-engine has a very good efficiency, especially at part load. A HCCI-combustion at all loads is possible in the Z-engine, with lambda about 1,7-2,2 and EGR-rate 15-45%, depending of the load. The TDC-temperature at part load is about 800 K and at full load (BMEP 30 bar) about 700 K. The HCCI-ignition, triggered with a pre chamber spark plug (88, 89) or small amount of fuel injection, occurs between 0° - 20° ATDC and this limits the pressure and maximal temperature. No knock is present, as the ignition occurs always at the right side of the NTC (negative temperature coefficient) regime (30,31 Intern EGR and active radicals stabilize the combustion (32-37) and lower the activation energy needed for the ignition.The robust HCCI-combustion without ignition problems (spark) has been validated with 2-stroke test engines in Dr. Zhengs Doctor Theses together with his research colleges in Drexel University, Philadelphia, USA, 2005, (36). The fuel consumption is: part load 192 g/kWh, best point 174 g/kWh and full load 188 g/kWh. The part load efficiency is much better than by PCI and RCCI, best point and full load values are of the same order. The explanation for the very good part load efficiency is the exergy increase, when the intercooled, compressed air is led in to the work cylinder and mixed with the hot, almost atmospheric combustion gases , having high intern energy, but almost zero exergy. The pressure increase at the end of the gas exchange increases also the efficiency.


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    HCCI combustion in the Z-engine

    Janhunen,T. / Aumet,FI | Kraftfahrwesen | 2014


    Dynamic Engine Control for HCCI Combustion

    Lahti, John / Moskwa, John | SAE Technical Papers | 2012


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    Janhunen,T. / Aumet Oy,FI | Kraftfahrwesen | 2010


    HCCI Combustion in DI Diesel Engine

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    Dynamic Engine Control for HCCI Combustion

    Lahti, J. / Moskwa, J. / Society of Automotive Engineers | British Library Conference Proceedings | 2012