Abstract: Abstract: One of the key points in diesel premixed combustion is the realization of combustion phasing control. The sensitivity of diesel to temperature and equivalent ratio was the crucial obstacle. In order to directly control the diesel premixed combustion phasing, a novel method called the jet controlled compression ignition (JCCI) for diesel premixed compression ignition was proposed. A single cylinder diesel engine was modified to study the JCCI system. First, a small ignition chamber comprising a gas fuel injector and a spark plug was mounted on the cylinder head in this diesel engine. Six small orifices were used to connect the ignition chamber and the main chamber. Furthermore, the compression ratio was reduced to 12 to avoid the auto-ignition of the premixed diesel fuel. Experiments were conducted on the JCCI engine under overall loads at a constant speed to study the trend of combustion and the emission characteristics of JCCI system. The results showed that the combustion phasing and emissions could be controlled by using the JCCI system. At medium load region whose brake's mean effective pressure was below 0.44 MPa, there was little change in the start phase of combustion and the midpoint phase of combustion and the combustion duration with the variation of load. The timing of jets issued from ignition chamber was controlled by spark timing. Therefore it meant that a direct control of the combustion phasing of diesel premixed combustion by employing spark timing in JCCI system could be expected. Due to a reduction of compression ratio and the relatively longer mixing time the combustion temperature was greatly reduced compared with that of original diesel engine. Then nitrogen oxide (NOx) was reduced accordingly. The maximum reduction of NOx was over 80% compared with that of original diesel during the medium high load region. At high load region whose brake's mean effective pressure was above 0.44 MPa, the controllability of jet was weakened with the load increasing as well as the linearity between spark timing and start phase of combustion and midpoint phase of combustion. The cylinder temperature increased as the load increased. When approaching full load, the cylinder was too high to avoid the auto-ignition of diesel mixture. It meant that the combustion of diesel mixture had begun before it was triggered by the jets issued from the ignition chamber. The combustion phasing was advanced greatly due to an auto-ignition of diesel mixture. Therefore the start phase of combustion and the midpoint phase of combustion and the combustion duration were reduced quickly with the load increasing. Furthermore, the acceleration of cylinder temperature increase could be expected and a great increase of NOx was caused as well. When approaching full load, NOx in JCCI was higher than that of original diesel engine. During overall load region, the smoke was maintained at a low level due to longer mixing time of diesel mixture compared with that in traditional diesel engine. The high emission of hydrocarbon (HC) and carbon monoxide (CO) could be seen during overall load region due to incomplete oxidation of fuel. The research can provide a reference for the control of diesel premixed combustion phasing.