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Problems such as higher heat load in the diesel engine and the occurrence of crazes within the valve bridge of heavy-duty vehicle diesel engine should be solved, with the increase of the power density of heavy-duty vehicle diesel engine. In this paper, the heat load experiment of complete machine, temperature-measuring of bottom part of cylinder head and the three-dimension numerical simulation on coolant flow and heat transfer in the water jacket have been performed. The result shows that the main reasons of higher heat load of the engine are insufficiency of heat-sinking capability of the water-radiator and shortage of coolant flux; and the unsuitable flow field in water jacket in cylinder head, where only a little of the coolant can cool the bottom of cylinder head, is the main cause of cylinder head bottom over-heated and thermal crack in the valve-bridge region.

Pure diesel and biodiesel were tested inside a constant-volume combustion chamber which simulates the in-cylinder conditions similar to a diesel engine and is more flexible to change the engine operation boundary conditions. The ambient temperature effect on flame lift-off length for both fuels was first investigated with fixed injection pressure, duration, ambient density, and ambient oxygen concentration. This was determined from time-averaged OH chemiluminescence imaging technique. Then, the impacts of the observed lift-off length variations on oxygen ratio upstream of the lift-off location and the soot formation process were also studied. A Forward Illumination Light Extinction (FILE) soot measurement technique was adopted to study the soot formation process. The FILE technique with the capability of two-dimensional time-resolved quantitative soot measurement provides the much-needed information to investigate the soot formation mechanism.