喷氢策略对射流点火天然气发动机燃烧特性的影响OA

To alleviate the challenges of ignition difficulty,slow flame propagation,and knock tendency in large-bore natural gas engines operating under lean-burn conditions,the effects of hydrogen-assisted turbulent jet ignition on reliable ignition and significantly acceleration of flame development were studied by computational fluid dynamics.The effects of single-injection strategies and double-injection strategies on jet characteristics and combustion performance were investigated at a fixed hydrogen energy fraction of 9％,with injection timings set at 330° and 90° crankshaft angle before top dead center(BTDC)of the pison compression stroke.The results show that the pressure difference between the pre-chamber and the main chamber increases initially and then decreases during the jet-ignition process.The single early-injection strategy exhibits the highest jet-flame velocity and temperature.Under the double-injection strategy,local flame quenching occurs near the orifices,and ignition is governed by the jet-flame mechanism.The jet flame develops a hydrogen-wrapped structure and exhibits combustion stratification characterized by locally fuel-rich zones and globally lean-burn regions.Compared with the baseline engine,the double-injection strategy increases the indicated thermal efficiency to 44.02％.As the mass of hydrogen introduced during the late injection(90° BTDC)increases,more unburned hydrogen is transported directly into the main chamber for combustion,resulting in an extended jet-ignition duration.At similar indicated thermal efficiency,the NOx specific emissions decrease by 24.26％.