Experimental analysis and multi-objective optimization of heavy-duty hydrogen SI engine performance and emissions based on GA-BP-MOGWO

Abstract

The heavy-duty hydrogen engine, as a key technology for achieving zero-carbon emissions, shows great development potential. The main problem of the hydrogen engine is high fuel consumption, high NOx emissions and hydrogen leakage. This study combined experimental and computational techniques to systematically study the effects of the excess air coefficient (λ) and spark timing (SPK) on the combustion, performance and emission characteristics of large-displacement multi-cylinder commercial hydrogen engines at a speed of 1200 r/min and throttle opening of 40 %. Further, the study explored the effects of key operating parameters on the hydrogen engine’s power characteristics (power), economic characteristics (Brake Specific Fuel Consumption, BSFC), and emission characteristics (NOx, Hydrogen Leakage). The experiment results reveal that the leaner the mixture, the better the economy, but it had adverse effect on power. The lowest BSFC of around 75 g/kWh is achieved when controlling λ at 2.8 and the SPK timing at approximately −30 °CA ATDC. Additionally, the lean mixture is conducive to reducing NOx emissions, and the minimum hydrogen leakage is located in a narrow area around λ at 2.2 and the SPK timing from −17 °CA ATDC to –33 °CA ATDC. In this paper, the complex relationship between independent variables (λ, SPK timing, intake pressure, CA50) and dependent variables (power, BSFC, NOx, Hydrogen Leakage) was established based on Genetic Algorithm-Back Propagation Neural Network (GA-BP) method. Finally, the study combined the Multi-Objective Grey Wolf Optimizer (MOGWO) algorithm and Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) to find the optimal trade-off between the performance and emissions of the hydrogen engine and obtain the optimal operating conditions. The multi-objective optimization results show that the NOx emissions and hydrogen leakage can be effectively reduced. Specifically, compared with the base condition (λ = 1.5, SPK timing = -1°CA ATDC), NOx was reduced about 95 % to 149.55 ppm, and hydrogen leakage was reduced about 88 % to 103.09 ppm, while increasing power up to 111.20 kW and reducing BSFC down to 78.34 g/kWh, a decrease of about 6.9 %. The above optimal result is obtained when controlling the operating conditions at λ of 2, SPK timing of −36 °CA ATDC, intake pressure of 129 kPa, and CA50 of 1°CA ATDC.