Investigation of Gasoline Compression Ignition (GCI) Combustion in a High Compression-Ratio Heavy-duty Single-Cylinder Diesel Engine

In this study, a high-efficiency heavy-duty diesel engine platform was used to evaluate gasoline compression ignition (GCI) operation. The experiment was carried out using a single-cylinder engine (SCE) of a high compression ratio (22:1). Pump-grade gasoline fuel 87 research octane number (RON) was used throughout engine testing. Injection strategy was established including double and triple injection schemes to optimize both engine efficiency and emissions. Both low-temperature heat release (LTHR) and high-temperature heat release (HTHR) were seen from a two-stage combustion event resulting from the interaction of pilot and main injections. At low load conditions, besides fuel stratification level by pilot/main injection strategy, higher in-cylinder pressure can greatly improve the ignition of 1^st stage combustion. As engine load increases, spray-wall interaction becomes more critical on engine efficiency and emissions performance. This was explored under two very different combustion systems: wave-like and stepped-lip pistons. Experimental results show that both combustion systems can deliver competitive diesel-like efficiency at lower soot emissions. NO_X emissions were controlled effectively with intermediate-to-high levels of exhaust gas recirculation (EGR). Other emissions species such as carbon monoxide (CO) and unburned hydrocarbon (UHC) from GCI combustion were slightly higher than that of diesel combustion. Low combustion instability and acceptable combustion noise were targeted and achieved under load sweep testing. Overall, this study further emphasizes that GCI combustion concept can be considered as part of the solutions for developing a high-efficiency and low emission combustion system.