Studies On Jet Controlled Diesel Premixed Charge Compression Ignition System

By synthesizing the advantages of gasoline and diesel engines, Premixed Charge Compression Ignition (PCCI) system with low temperature combustion can achieve ultra-low NOx and PM emissions as well as high efficiency. One of the key obstacles that preventing PCCI from practical use is the control of its combustion phasing. To achieve a direct ignition control of diesel premixed mixture, the Jet Controlled Compression Ignition (JCCI) combustion system was proposed and developed. Triggered with the jets issued from an ignition chamber, the ignition of diesel premixed diesel charge can be directly controlled.A JCCI experimental engine was developed based on a single-cylinder diesel engine CF186FA. The design criterions of the ignition chamber in JCCI combustion system were determined, based on which the ignition chamber and gas fuel supply system was designed and installed in the cylinder head. The shape of piston cavity was modified from the deep co type to a shallow bowl shape which is suitable for premixed combustion and the compression ratio was reduced. High disturbance nozzles combined with early injection strategy was used to form uniform premixed charge. Using CompactRIO platform, the gas injection and spark timing control programs were developed based on the crank angle signal. Using a combination of state machine and producer-consumer, cylinder pressure can be measured simultaneously with gas fuel injection and ignition control. The off-line combustion analysis system was developed using hybrid program of Matlab and Lab VIEW.The experimental results of JCCI engine showed good linear relationships between spark timing and CA10or CA50at most operating conditions, and ignition delay was not sensitive to load, indicating no auto-ignition in main combustion chamber before jet injected from the ignition chamber, and the combustion system possesses the ability of direct combustion phasing control. At about full load, the ignition delay decreased and are a relative early auto-ignition in the main combustion chamber was observed due to high in-cylinder temperature as well as relatively high compression ratio. At these conditions, ignition and combustion of the diesel mixture were controlled by the in-cylinder thermal conditions. Without inlet boost and EGR, the NOx and smoke in JCCI engine with mechanical fuel injection pump were reduced greatly. The max reductions of them were both over90%compared with the original diesel engine.The simulation results of JCCI showed that most of the flame was quenched after passing through the small orifices of the ignition chamber. Then the combustion in the main chamber was initiated around the high temperature radical jets. Due to the absence of flame propagation, the multiple auto-ignition sites can be expected as well as the low temperature and low NO emissions.The high pressure common rail system was used to replace the mechanical fuel injection system. The preliminary experimental results showed that the maximum reduction of NOx was over90%at relatively high load and the smoke was almost zero. At high load, the maximum reduction of NOx was near80%, and the smoke was also very low. The brake thermal efficiency was a little higher than that of original diesel engine.