Computational optimization of a hydrogen direct-injection compression-ignition engine for jet mixing dominated nonpremixed combustion

Abstract

Hydrogen (H2) nonpremixed combustion has been showcased as a potentially viable and preferable strategy for direct-injection compression-ignition (DICI) engines for its ability to deliver high heat release rates and low heat transfer losses, in addition to potentially zero CO2 emissions. However, this concept requires a different optimization strategy compared to conventional diesel engines, prioritizing a combustion mode dominated by free turbulent jet mixing. In the present work, this optimization strategy is realized and studied computationally using the CONVERGE CFD solver. It involves adopting wide piston bowl designs with shapes adapted to the H2 jets, altered injector umbrella angle, and an increased number of nozzle orifices with either smaller orifice diameter or reduced injection pressure to maintain constant injector flow rate capacity. This work shows that these modifications are effective at maximizing free-jet mixing, thus enabling more favorable heat release profiles, reducing wall heat transfer by 35%, and improving indicated efficiency by 2.2 percentage points. However, they also caused elevated incomplete combustion losses at low excess air ratios, which may be eliminated by implementing a moderate swirl, small post-injections, and further optimized jet momentum and piston design. Noise emissions with the optimized DICI H2 combustion are shown to be comparable to those from conventional diesel engines. Finally, it is demonstrated that modern engine concepts, such as the double compression-expansion engine, may achieve around 56% brake thermal efficiency with the DICI H2 combustion, which is 1.1 percentage point higher than with diesel fuel. Thus, this work contributes to the knowledge base required for future improvements in H2 engine efficiency.

Optimization of Hydrogen Injection Flow Rate for Hydrogen Internal Combustion Engines Based on IQGA

“…The mass flow rate of hydrogen injection is determined by both the nozzle diameter and the hydrogen injection pressure. Reducing the nozzle diameter and the hydrogen injection pressure alone can reduce the intake blockage caused by hydrogen expansion [16][17][18]. In order to solve the problem of intake blockage in hydrogen internal combustion engines, this article uses quantum genetic algorithm and improved quantum genetic algorithm to optimize the nozzle diameter and hydrogen injection pressure, find the optimal nozzle diameter and hydrogen injection pressure, and then solve the problem of intake blockage.…”

Introduction to the current and future use of H2 and H2-based e-fuels in combustion engines and fuel cells Special Issue

“…Papers in the no-carbon emission group touch on topics such as: the efficiency of hydrogen fuel cell vehicles under real-world operating conditions, 1 the use of hydrogen in internal combustion engines in both spark-ignited and compression ignition operation, [2][3][4] the concept of a split-cycle hydrogen engine with argon as the working fluid 5 and the use of ammonia in a spark-ignited engine. 6 A number of papers focused on intermediate-term solutions that would be accompanied by some engine-out carbon emissions.…”

“…the use of hydrogen in internal combustion engines in both spark-ignited and compression ignition operation, 2–4…”

Experimental Investigation on Indicated Pressure and Heat Release for Direct Hydrogen Injection in a Dual Fuel Diesel Engine

“…It is also focused there that the reasons for observed changes in the combustion process are not explained. The hydrogen combustion process is very interestingly presented in the paper [33]. Using a computational solver, the authors analyzed the pure hydrogen combustion as a potentially cost-effective and preferred strategy for direct injection compression ignition engines, due to its ability to achieve high heat release rates and low heat transfer losses, as well as potentially zero CO 2 emissions.…”