Effects of Equivalence Ratio on High-Compression Boosted HCCI Combustion Characteristics

Homogeneous charge compression ignition (HCCI) combustion offers significant thermal efficiency benefits but faces challenges in combustion phasing control and operating range limitations. This study investigates the effects of equivalence ratio variation on combustion characteristics, pressure development, temperature evolution, and indicated work output in an HCCI engine operating at high compression ratio (۲۱:۱) with ۲ bar intake pressure. CHEMKIN simulations were performed across a wide equivalence ratio range (φ = ۰.۲۲–۰.۳۴) to capture both lean and near-stoichiometric operating conditions. Results reveal two distinct combustion regimes: for lean mixtures (φ ≤ ۰.۲۶), CA۵۰ remains nearly constant at ۳۶۳.۶–۳۶۳.۷°CA with total combustion duration of approximately ۶.۵°CA, while peak temperatures stabilize at ۱۵۵۰ K. For richer mixtures (φ ≥ ۰.۳۰), combustion accelerates significantly, with CA۵۰ advancing to ۳۶۲.۲–۳۶۲.۴°CA and duration shortening to ۳.۱°CA, accompanied by peak temperatures rising sharply to ۱۷۵۰ K at φ = ۰.۳۴. Cylinder pressure increases monotonically with equivalence ratio, reaching ۲۹۵ bar at φ = ۰.۳۴, while normalized indicated work shows progressive improvement across the entire range. The consistent CA۱۰ timing (۳۶۰.۸–۳۶۱.۱°CA) across all conditions confirms that combustion onset is governed primarily by compression thermodynamics rather than mixture strength. These findings demonstrate that CR = ۲۱:۱ combined with ۲ bar boost enables stable HCCI operation from ultra-lean to rich conditions, with φ = ۰.۳۰ representing an optimal balance between work output and thermal management.

کلیدواژه ها:

HCCI engine ، CNG ، equivalence ratio ، combustion phasing ، CHEMKIN