Exergy analysis of the lean-burn hydrogen-fuelled engine

Abstract

Hydrogen is considered an alternative fuel for use in internal combustion engines. The internal combustion engine will likely remain in use for vehicle and stationary applications for the foreseeable future, therefore identifying and quantifying efficiency losses of burning fuels is important. Exergy analysis is a method for investigating the fundamental origins of losses, the limits to efficiency, and the engineering trade-offs required to reduce losses. This comprehensive exergy analysis of a boosted lean-burn hydrogen spark ignition engine investigates the processes involving exergy destruction under real-world conditions. This efficiency of a hydrogen SI engine and the NO emissions are evaluated by quantifying the exergy destruction for various intake manifold air pressures, lean-burn mixtures, compression ratios, and spark timings. Using an improved two-zone engine model to study in-cylinder processes, the results indicate that increasing air dilution enhances exergy transfer to work, due mainly to diverting exhaust exergy into reversible work. However, increasing air dilution also increases combustion-related exergy destruction due to greater entropy generation for leaner mixtures, but reducing heat loss decreases combustion-related irreversibility. Higher manifold air pressures and compression ratios increase the quantity of exergy directed to work and heat, whilst reducing exergy expelled to exhaust. Gaining understanding of the detail of thermodynamic mechanisms of the routes by which the work potential is lost potentially assists in engineering improvements to minimize exergy losses, and to increase efficiency and work output.