Abstract: Abstract: Homogeneous charge induced ignition (HCII) is an effective way to reduce NOx emission and soot emission simultaneously while keeping high thermal efficiency. However, the former research about it was limited to single cylinder engine which was original or modified by multi-cylinder engine. Usually, separate intake system, exhaust system and fuel supply system would be set up for the test cylinder, while fuel supply to the other cylinders was cut off. Thus, there was only the test cylinder working normally for the experimental engine. Besides, a fuel-free air compressor, as an external equipment not belonging to the engine body, was used to replace turbocharger. Therefore, the experimental condition of intake-exhaust, EGR (exhaust gas recirculation) - turbocharger coupling effect and mechanical loss was quite different from which engines actually worked in. To study the real emission performance of HCII, a six-cylinder turbocharged diesel engine was modified to achieve MHCII (multi-cylinder homogeneous charge induced ignition, which means all cylinders operate in HCII mode simultaneously) in this paper. The experimental engine incorporated an extra gasoline injection system, and the technology of intake port MFI (multi-point fuel injection) was used, while diesel injection kept the original high pressure common rail system without any change. Furthermore, a dual-fuel ECU (electronic control unit) that could be adjusted flexibly was equipped to control both of the fuels. The whole research in this paper included 2 aspects. Firstly, the influence of gasoline ratio and EGR ratio on MHCII was studied in a typical engine working condition, i.e. rotating speed of 1 438 r/min and IMEP (indicated mean effective pressure) of 0.7 MPa. Based on it, the basic principles of optimizing these 2 parameters were established. Secondly, DOC (diesel oxidation catalyst) device was matched to the experimental engine and the ESC (European steady state cycle) test was conducted under the guidance of those principles established in the first step. Test results of the first step showed that even 90% gasoline in total fuel energy could control the combustion phase sufficiently. With the gasoline ratio increasing, the percentage of pre-mixed combustion got larger and the shape of heat release rate curve changed from double peaks to one peak, in the meantime, NOx emission and soot emission both decreased dramatically. However, gasoline ratio could not get large indefinitely, or it would cause the problem of rise rate of maximum pressure increasing sharply. In the experimental condition, the maximum gasoline ratio should be less than 90%. With EGR ratio increasing, the combustion of lean gasoline homogeneous charge, as the major component of total fuel, was improved, in the meantime, combustion efficiency and effective thermal efficiency both got larger, so the combustion of MHCII could be optimized under suitable EGR ratio. However, similar to gasoline ratio, excessive EGR ratio would make the effect of diesel combustion deterioration prominent, so the maximum EGR ratio should still be controlled at around 30%. With EGR ratio increasing, the NOx emission decreased while soot emission remained nearly unchanged, and thus larger EGR ratio could be applied to inhibit NOx formation. Test results of ESC showed that the specific emissions of NOx, CO (carbon monoxide) and THC (total hydrocarbon) could reach 1.89, 0.90 and 0.12 g/(kW·h), meeting China Ⅴ limits of 2.00, 1.50, and 0.46 g/(kW·h) separately, only with the aid of DOC. In the meantime, the weighted value of soot, calculated from summing the product of soot emission and weighting coefficient at each ESC test point, was also at an extremely low level of 0.034 m-1. Therefore, MHCII can reduce the emission of whole diesel engine significantly and it is highly possible to meet all the requirements of China Ⅴ emission standard under steady state test.