Assessment of cycle-to-cycle variations in hydrogen fueled internal combustion engine

Cycle-to-cycle variations in spark ignition (SI) internal combustion engines (ICE) fueled with hydrogen (H 2 ) were investigated in the context of enhancing combustion stability. In the first part, the effects of boost pressure, exhaust gas recirculation (EGR), spark advance (SA), and lambda on cycle-to-cycle variations based on Matekunas plots were investigated. In the second part, the integral of the coefficient of variation of pressure (COV P ) curve (ICOV) by varying SA, equivalence ratio (ER), and volumetric efficiency (VE) were examined and their impacts were evaluated. The experimental data were acquired through a test campaign performed on a single-cylinder PFI-SI ICE for 100 consecutive cycles. The Matekunas plots showed that as combustion stability increases, cycle-to-cycle variations decrease, and vice versa. Additionally, a decrease in cycle-to-cycle variations is accompanied by a decrease in maximum pressure ( P max ) values. The increase in the maximum value of COV P results in the increase of the ICOV with a relatively strong linear relationship demonstrated by correlation coefficient (CC) of 0.62 between ICOV and COV P . Therefore, it can be concluded that if the COV P is higher, it results in high cycle-to-cycle variations. The higher values of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>P</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>max</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> lead to high COV P with a strong linear correlation coefficient (CC) value of 0.78 between P max and COV P . As SA and VE increase, and ER decreases, cycle-to-cycle variations during combustion duration increase, concluding less repetitive combustion.