Combustion and Emission Behaviour of a HCCI Wankel Engine Across Lambda Variations: Insights for Future Aviation-Oriented Rotary Engine Concepts

Year 2025, Volume: 9 Issue: 4, 626 - 636, 31.12.2025

Ömer Türkcan , Seyfi Polat

https://doi.org/10.30939/ijastech..1821778

Abstract

This study examines the combustion and emission behavior of a four-stroke Wankel rotary engine operated in Homogeneous Charge Compression Ignition (HCCI) mode using n-heptane fuel over excess-air ratios of λ = 2.2–2.8. A validated three-dimensional CONVERGE CFD model of the Mazda Renesis RX-8 13B MSP engine—verified against experimental spark-ignition pressure data—was used to assess HCCI performance. The simulations employed semi detailed chemistry (SAGE), Renormalization Group (RNG) k–ε turbulence modelling, and adaptive mesh refinement to capture the multi-stage auto-ignition process. The analysis encompassed key combustion and emission indicators, including in-cylinder and peak pressure, heat-release rate, cumulative heat-release behavior, maximum pressure-rise rate, combustion-phasing metrics crank angle at 10% of total heat released (CA10), crank angle at 50% of total heat released (CA50), crank angle at 90% of total heat released (CA90), combustion duration, and major exhaust species carbon monoxide (CO), carbon dioxide (CO2), hydrocarbons (HC) and nitrogen oxides (NOₓ). Stable HCCI operation was achieved only within a narrow range: λ = 2.2–2.8. Richer mixtures exceeded the 10 bar/°CA knock-related pressure-rise-rate limit, while leaner mixtures resulted in misfire. Increasing λ delayed auto-ignition, weakened high-temperature oxidation, and extended combustion duration. CO and HC emissions rose with λ due to reduced combustion temperature and strong near-wall quenching driven by the Wankel chamber’s high surface-to-volume ratio, whereas NOx remained extremely low and nearly eliminated for λ ≥ 2.4. Overall, the findings confirm that HCCI can be successfully realized in a Wankel rotary engine with ultra-low NOx emissions, provided operation remains within its narrow λ window. These results underscore the potential of Wankel HCCI concepts for lightweight aviation and unmanned aerial vehicle (UAV) propulsion, while highlighting the need for improved mixture preparation and combustion-phasing control for practical implementation.

Keywords

Aviation , hcci , wankel , Rotary , Engine , combustion , emissions

Thanks

The authors thank to Convergent Science for providing CONVERGE Academic licenses and technical support for this work.

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