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Hydrogen is a clean and renewable alternative fuel. In this paper, the combustion mechanism of diesel/hydrogen dual fuel is constructed and verified. The mechanism is combined with three-dimensional numerical simulation to study the effects of pilot injection and main injection on the combustion and emissions of a diesel/hydrogen dual fuel engine. The mechanism uses a 70% mole fraction of n-decane and 30% mole fraction of α-methylnaphthalene as diesel substitutes, and it combines n-decane, α-methylnaphthalene, NOX, PAH, soot and H2/C1-C3 sub-mechanisms to form a diesel/hydrogen dual fuel combustion mechanism. The mechanism was verified by chemical kinetics, including the ignition delay time, JSR (Jet Stirred Reactor) oxidation and laminar flame speed, and then, it was verified by computational fluid dynamics. The results show that the simulated values are in good agreement with the experimental values of cylinder pressure, heat release rate and emissions data. The mechanism can well predict the combustion and emissions of a diesel/hydrogen dual fuel engine. Compared with single injection, the peak heat release rate, peak cylinder pressure and MPIR (Maximum Pressure Rise Rate) increase with the increase in pilot mass percent from 5% to 20%, which makes the phase of CA10 and CA50 advance and reduces CO emissions, but NOX emissions increase. With the advance of pilot injection timing from 10° CA BTDC to 30° CA BTDC, the peak cylinder pressure increases, the peak heat release rate decreases, CA10 and CA50 advance, CO emissions decrease, NOX emissions increase and NOX emissions peak at 30° CA BTDC. When the pilot injection timing is further advanced from 30° CA BTDC to 50° CA BTDC, the peak cylinder pressure decreases, the peak heat release rate increases, CA10 and CA50 are delayed, CO and NOX emissions are reduced, and NOX emissions at 50° CA BTDC are lower than those at 10° CA BTDC. With the advance of main injection timing from 0° CA BTDC to 8° CA BTDC, CO emissions decrease, NOX emissions increase, the peak cylinder pressure increases, the peak heat release rate decreases slightly first and then increases, and the peak cylinder pressure and peak heat release rate corresponding to the overall phase shift forward. When the main injection timing is advanced to 6° CA BTDC, MPIR is 1.3 MPa/° CA, exceeding the MPIR limit of diesel engine 1.2 MPa/° CA.

Predictive simulations of liquid pool fires are based on the previous experimental study from a reduced mechanically ventilated enclosure with a length/height and width of 2 m. An external ventilation system provides an air supply rate ranging from 24 to 40 m 3 /h, corresponding to 3 and 5 Air Change Per Hour (ACPH), respectively. A circular heptane or dodecane pan with a diameter varying from 23 to 40 cm is placed in the middle of the enclosure. The proposed liquid evaporation model in combustion environments is fully coupled with CFD simulation. The results show that the fuel pan above 30 cm leads to faster fire growth implying more important peak up to 200 kW in heat release rate and thus more dangerous fire. In the early stages of a fire, a stratified hotter unburnt fuels layer with a concentration beyond the Lower Flammability Limit (LFL) is formed in the extraction duct connected to a mechanically ventilated enclosure fire. With a long time delay (about 21 min in the current study), the energy released per mass of oxygen consumed allows to raise the smoke temperature above 350°C. Occurrence of flame extinction in vitiated air enclosure with an oxygen concentration below 5% makes a sudden decrease of the pressure level inside enclosure due to cooling effects. This induces a sudden supply of fresh air from dilution duct, providing a sufficient oxygen concentration with a molar fraction of about 10% for triggering the ignition of a hotter fuel-air mixture near the extraction duct. Such auto-ignition, determined experimentally by visual identification of fire, is likely a random phenomenon with a probability of 50% due to the heat leakage through the walls of the experimental facility. When the compartment is more heat-tight by using an insulating material, the auto-ignition occurs for each fire tests. Globally, the phenomena with ignition near the extraction duct can be identified by a rapid decrease of unburnt fuel concentration towards a stoichiometric fuel-air mixture and a sharp increase of temperature with a peak reaching a typical flame temperature of 550°C there.