Experimental evaluation of pre-ignition and multi-objective optimal controlling of turbocharged direct injection hydrogen engines under high-load and high-speed conditions using Taguchi and TOPSIS methods

Hydrogen demonstrates potential as a renewable energy source for internal combustion engines due to its carbon-free nature and high efficiency. However, the risk of abnormal combustion arises in downsized, turbocharged hydrogen internal combustion engines (H₂ICE), particularly manifesting as low-speed pre-ignition and super knock at high loads and high speeds. In this paper, the characteristics of slight and distinct pre-ignition are identified and analyzed by experiments in a 1.5 L turbocharged direct injection H₂ICE. Taguchi method and analysis of variance are employed to show that frequent pre-ignition begins to occur when the load of brake mean effective pressure (BMEP) of 1.0 MPa at 2500 rpm. Intense pre-ignition tends to happen with a BMEP exceeding 1.4 MPa at 2500 rpm and 5500 rpm. Specific control strategies are also explored to suppress pre-ignitions and enhance engine performance, considering brake thermal efficiency (BTE), coefficient of variation (CoV_IMEP), maximum amplitude of pressure (MAPO), and nitrogen oxides (NOx) emissions in a synergistic method. Additionally, six evaluation indices from the Technique for Order Preference by Similarity to the Ideal Solution (TOPSIS) are ranked to find the multi-objective optimal controlling at different working conditions. The results indicate that increasing λ and delaying ignition timing can reduce 88.7 % pre-ignition numbers and enhance 1.4 % BTE when the BMEP = 1.0 MPa at 2500 rpm. Optimizing split injection (SEOI = −40°CA, SIMP = 35 %) suppress the pre-ignition frequent by 94.4 % and the pre-ignition intense by 81.7 %, while the maximum BTE is improved to 42.02 % when the BMEP = 1.4 MPa at 2500 rpm. In terms of high-speed of 5500 rpm working conditions, optimal variable valve timing (VVT: IVO = 20°CA, EVC = −20°CA) strategies are applied to reach the peak power of 120 kW with no abnormal combustion. The proposed method and controlling strategy of this paper are valuable to developing a large-power H₂ICE with stable combustion and high efficiency when managing and conversing hydrogen energy.