Computational study of added H2 impacts on mixture formation, OH radical and unregulated emissions of spark-ignition methanol engine under various boundary parameters

Numerical simulations of hydrogen (H-2) impacts on mixture formation, OH radical generation, and formaldehyde (HCHO) and unburned methanol (CH3OH) emissions of spark-ignition (SI) methanol engine based methanol late-injection strategy under different methanol injection timings (MIT), ignition timings (IT), excess air ratios (lambda) and added H-2 ratios (R-H2) boundary parameters were conducted. The simulation results show that the ideal methanol concentration distribution is obtained at the MIT = 85 degrees CA BTDC. The OH radical plays a dominant role in methanol oxidation. The OHPMF (peak OH radical mass fraction) of R-H2 = 9 % >> OHPMF of R-H2 = 6 % > OHPMF of R-H2 = 3 % > OHPMF of R-H2 = 0 % at MIT = 85 degrees CA BTDC. Compared with IT and lambda, the R-H2 is more decisive for the generation of OH radical. The HCHO is a major intermediate and an important unregulated emission of methanol engine. In the initial stage of methanol reaction, added H-2 can accelerate the generation of OH radical, further promote the oxidation of methanol, and greatly raise the generation of HCHO. The peak HCHO mass fraction increases with the increase of R-H2. At MIT = 85 degrees CA BTDC and exhaust valve opening, the HCHO emission of R-H2 = 3 %, 6 %, and 9 % is approximately 51 %, 76.5 % and 89.4 % lower than that of R-H2 = 0 %, respectively. The generation and post-oxidation of HCHO mainly depended on average in-cylinder temperature. There is a lowest CH3OH emission at MIT = 85 degrees CA BTDC, IT = 28 degrees CA BTDC, lambda = 1.4 and pure methanol. At MIT = 85 degrees CA BTDC, lambda = 1.4 and exhaust valve opening, the CH3OH emission of R-H2 = 3 %, 6 %, and 9 % is approximately 52.8 %, 75.5 % and 92.5 % lower than that of R-H2 = 0 %, respectively.