Experimental study of cycle-by-cycle variations in a spark ignition internal combustion engine fueled with hydrogen

High fluctuations in the combustion process from one cycle to another, referred to as cycle-by-cycle variations, can have adverse effects on internal combustion engine performances, particularly in spark ignition (SI) engines. These effects encompass incomplete combustion, the potential for misfires, and adverse impacts on fuel economy. Furthermore, the cycle-by-cycle variations can also affect a vehicle's drivability and overall comfort, especially when operating under lean-burn conditions. Although many cycle-by-cycle analyses have been investigated extensively in the past, there is limited in-depth knowledge available regarding the causes of cycle-by-cycle (CbC) variations in hydrogen lean-burn SI engines. Trying to contribute to this topic, the current study presents a comprehensive analysis of the CbC variations based on the cylinder pressure data. The study was carried out employing a hydrogen single-cylinder research SI engine. The experiments were performed by varying more than fifty operating conditions including the variations in lambda, spark advance, boost pressure, and exhaust gas recirculation, however, the load and speed were kept constant throughout the experimental campaign. The results indicate that pressure exhibits significant variations during the combustion process and minor variations during non-combustion processes. In the period from the inlet valve close till the start of combustion, pressure exhibits the least variations. The coefficient of variation of pressure (COVP) curve depicts three important points in H2-ICE as well: global minima, global maxima, and second local minima. The magnitude of the COVP curve changes across all the operating conditions, however, the shape of the COVP curve remains unchanged across all the operating conditions, indicating its independence from the operating condition in an H2-ICE. This study presents an alternative approach for a quick combustion analysis of hydrogen engines. Without the need for more complex methodologies like heat release rate analysis, the presented cylinder pressure cycle-by-cycle analysis enables a quick and precise identification of primary combustion features (start of combustion, center of combustion, end of combustion, and operation condition stability). Additionally, the engine control unit could implement these procedures to automatically adjust cycle-by-cycle variations, therefore increasing engine efficiency.