Parametric study on effects of excess air/fuel ratio, spark timing, and methanol injection timing on combustion characteristics and performance of natural gas/methanol dual-fuel engine at low loads

• Published in: Energy conversion and management 2020-04, Vol.210, p.112742, Article 112742
• Main Authors: Chen, Zhanming, Chen, Hao, Wang, Long, Geng, Limin, Zeng, Ke
• Format: Article
• Language: English
• Subjects: Air-fuel ratio; Coefficient of variation; Combustion; Dual fuel; Excess air/fuel ratio; Flame propagation; Fuel mixtures; Homogeneous mixtures; Injection; Methanol; Methanol injection timing; Natural gas; Parametric statistics; Thermodynamic efficiency
• ISSN: 0196-8904; 1879-2227
• DOI: 10.1016/j.enconman.2020.112742

•CA0-10 and CA10-90 of natural gas engine are shortened with methanol addition.•Lean-burn capability of natural gas are improved by adding methanol.•The most appropriate MIT is set at the timing of 60 °CA after the intake valve closed. A parametric investigation of the effects of excess air/fuel ratio (λ), spark timing (ST), and methanol injection timing (MIT) on the combustion characteristics and performance of a natural gas/methanol dual-fuel engine was conducted. The operation was carried out at 1600 rpm and a low load. λ was varied from 1.2 to 1.6, in increments of 0.1. The ST was kept close to the optimized value of brake thermal efficiency (ηet) and varied from advanced by an 8° crank angle (8 °CA) to retarded by 8 °CA. The results indicated that the flame development period (CA0-10) and the flame propagation period (CA10-90) were prolonged when λ increased from 1.2 to 1.6. The prolonged CA0-10 and CA10-90 could be shortened via the addition of methanol. ηet increased with an increase in λ and the methanol energy substitution ratio (MSR). The ST corresponding to the maximum value of ηet was delayed with an increase in the MSR. When the MIT is changed from −720 to 0 °CA BTDC, two types of air–fuel mixtures can be formed: a stratified-like mixture (when the MIT is set at the timing of intake only) and a homogeneous mixture (when the MIT is set at the timing of the intake valve closing). The most suitable MIT proved to be approximately 60 °CA after the intake valve closed. When the MIT was set at this point, CA0-10 and CA10-90 were shortened, and the coefficient of variation in the indicated mean effective pressure was reduced.