Efficiency improvement investigation through Miller cycle strategy for SI engine operating on stoichiometric producer gas and methane blends

Abstract

Decentralized power generation through gasifier-engine system is an attractive alternative for reducing environmental impact and power grid dependency. For effective sewage sludge-waste to end-use electricity generation by engine integration, this work aims to simulate and investigate thermal efficiency enhancement in SI engine by employing late inlet valve close (LIVC) strategy with 12.0:1 geometrical compression ratio miller cycle and operating engine with sewage sludge-based producer gas (SSPG) by blending methane in various proportions. A quasi-dimensional thermodynamic model is simulated to explore SI engine performance, after validation from an experimental reference. Effects of blending SSPG to methane, varying LIVC and spark timing were analyzed respective to indicated thermal efficiency (ITE), indicated power (IP), brake thermal efficiency (BTE), brake power (BP), brake-specific energy consumption (BSEC) and emissions (CO and NO). Parametric results were found in trade-off nature of performance corresponding to engine efficiency and power. Thus, response surface methodology (RSM) was applied to find the best operating conditions for enhancing performance and diminishing emissions of the blended fuel SI engine. 64.7 % SSPG Blend, 70.33⁰ (ABDC) LIVC, and 34.03⁰ (BTDC) SOI were found as optimum operating parameters corresponding to the generated optimal responses of 35.47 % ITE, 5.18 kW IP, 27.95 % BTE, 4.08 kW BP, 12.671 MJ/kWh BSEC, and 0.688 V% CO, 1456.93 ppm NO emissions. The ANOVA-based regression model shows composite desirability of 0.8 with 95 % confidence level. In summary, the optimization method and optimal operation parameters offer significant reference for improving engine performance for high CR miller cycle-based LIVC approach.