Extension of an operating load range of a four-cylinder gasoline homogeneous charge compression ignition engine via a blowdown supercharge system, aiming at in-cylinder thermal stratification

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Abstract
In order to extend the operational range with a gasoline fueled multi-cylinder homogeneous charge compression ignition engine, a blowdown supercharge system and an exhaust gas recirculation guide was developed. The concept was to provide a large amount of diluted mixture and a strong in-cylinder thermal stratification for decreasing nitrogen oxide emissions and pressure rise rate during high-load homogeneous charge compression ignition operation. Secondary air injection was also proposed to reduce a cylinder-to-cylinder variation in ignition timing, which is one of the limiting factors of multi-cylinder homogeneous charge compression ignition operation. In advance of experimental works, the blowdown supercharge system and the exhaust gas recirculation guide were proved to be effective to reduce pressure rise rate for high-load operation using three-dimensional in-cylinder flow simulations and zero-dimensional multi-zone simulations with detailed chemical kinetics. Based on the simulation results, experiments were conducted using a slightly modified production four-cylinder gasoline engine. At first, the effects of the proposed techniques were experimentally investigated by focusing on one cylinder out of four. Then, a four-cylinder homogeneous charge compression ignition operation test using the new techniques was carried out. The one-cylinder measurements revealed that the blowdown supercharge system with an exhaust gas recirculation guide is capable of extending the homogeneous charge compression ignition operating range up to a net indicated mean effective pressure of 590 kPa for naturally aspirated conditions. In addition, secondary air injection was experimentally demonstrated as a technique for reducing a cylinder-to-cylinder variation in ignition timing. Reducing the cylinder-to-cylinder variation in ignition timing, four-cylinder homogeneous charge compression ignition operation with a net indicated mean effective pressure of 570 kPa was successfully achieved with the blowdown supercharge system and the exhaust gas recirculation guide.

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