Due to the simplicity of the exhaust gas aftertreatment system, the heavy-duty natural gas spark ignition (SI) engines play an important role in achieving the macro targets of the reduction of petroleum consumption, carbon and harmful emissions. Considering that power-to-methanol is economically more feasible than power-to-methane, methanol is proposed to continue the advantages of natural gas engines. Based on the fuel properties of methanol and our researching experience, methanol mixture preparation and flow within the cylinder are the most significant. A novel high-pressure port fuel injection (PFI) system is utilized to promote atomization and evaporation of methanol. The effects of the injection strategy, including injection pressure (p_inj) and injection timing (α_inj), and excess air–fuel ratio (λ) on the mixture formation were simulated and then studied by engine experiments.

Three-dimensional simulation and engine tests were conducted under the condition of 1500 rpm and the brake mean effective pressure (BMEP) of 0.854 MPa. p_inj varied from 8 MPa to 24 MPa by 4 MPa, α_inj was from 240°CA BTDC to 400°CA BTDC by 40°CA and λ was set to be 1.1,1.2 and 1.3, respectively. Simulation results indicate that the mixture homogeneity can be promoted by the optimized injection strategy. The mixture is the most homogeneous at α_inj = 340 °CA BTDC and p_inj = 8 MPa and the most inhomogeneous at α_inj = 400 °CA BTDC and p_inj = 24 MPa when λ = 1.2. The experimental results indicate that the more homogeneous mixture can improve engine brake thermal efficiency by shortening CA_0-10 and CA_10-90 as well as methanol lean-burn. The optimized injection strategy can improve the brake thermal efficiency by 2.6%, 2.7% and 2.8% when λ = 1.1, 1.2 and 1.3, respectively.

由于废气后处理系统的简单性，重型天然气火花点火（SI）发动机在实现降低石油消耗、碳排放和有害排放的宏观目标方面发挥着重要作用。考虑到动力制甲醇比动力制甲烷在经济上更可行，因此建议采用甲醇来延续天然气发动机的优势。根据甲醇的燃料特性和我们的研究经验，甲醇混合气的制备和气缸内的流动是最重要的。新型高压进气道燃油喷射 (PFI) 系统用于促进甲醇的雾化和蒸发。喷射策略的影响，包括喷射压力 (p _inj ) 和喷射正时 (α _inj)，以及过量空燃比 (λ) 对混合气形成的影响，然后通过发动机实验进行研究。

在1500 rpm、制动平均有效压力（BMEP）为0.854 MPa的条件下进行三维仿真和发动机试验。p _inj从 8 MPa 到 24 MPa 变化 4 MPa，α _inj从 240°CA BTDC 到 400°CA BTDC，变化 40°CA，λ 分别设置为 1.1、1.2 和 1.3。仿真结果表明，优化后的喷射策略可以促进混合气的均匀性。混合物在 α _inj  = 340 °CA BTDC 和 p _inj  = 8 MPa 时最均匀，在 α _inj  = 400 °CA BTDC 和 p _{inj 时}最不均匀 = 24 MPa 当 λ = 1.2 时。实验结果表明，更均匀的混合气可以通过缩短 CA _0-10和 CA _10-90以及甲醇稀燃来提高发动机制动热效率。当λ=1.1、1.2和1.3时，优化后的喷射策略可使制动热效率分别提高2.6%、2.7%和2.8%。