Towards better correlation between optical and commercial spark ignition engines through quasi-dimensional modeling of cycle-to-cycle variability

Abstract

Internal combustion engines are still the main choice when considering propulsion technology in the transport sector. Spark ignition (SI) units offer the advantage of good efficiency with simpler after-treatment systems. Lean operation is a promising strategy that would further improve efficiency, but requires mitigation of cycle-to-cycle variability (CCV). Within this context, and given the increasing trend of using simulation based evaluations during engine development, the current work investigated combustion in an optical SI engine through measurements and quasi-dimensional simulation. The possibility of visualizing in-cylinder processes provides unique insight, but also introduces complications with respect to commercial engines. For this reason, quasi-dimensional simulation was applied so as to better understand the factors that induce CCV. For the specific case of the investigated engine, cycle-to-cycle measured exhaust air-fuel ratio was found to be directly correlated to variations of engine output. Several routes of incorporating these effects into simulations were evaluated. Introducing a random component in the period of laminar-turbulent flame transition was found to ensure good grounds for simulating peak pressure variability. Indicated mean effective pressure (IMEP) on the other hand was found to depend less on the initial stages of combustion and was strongly correlated to aforementioned variability of exhaust air-fuel ratio.

Combustion Diagnosis in a Spark-Ignition Engine Fueled with Syngas at Different CO/H2 and Diluent Ratios

“…Currently, the primary focus of research on syngas-powered engines is centered around optimizing the engines to the fullest potential and enhancing numerical models [14]. Optically accessible engines provide results that can be used to benefit both endeavors, thereby enabling the development of advanced solutions for the optimization of engines, such as the ones developed by Irimesco [19] or Merola et al [20], which can be applied in the development of more efficient commercial engines. The authors of this work have shown in recent studies that the addition of methane to syngas will favor the stability of the flame and the conversion efficiency [15], while the addition of hydrogen will improve not only the flame stability but also its emissions [16,21,22].…”