Effects of dual-spark ignition system with two different piston bowl shapes on combustion and efficiency in a single-cylinder engine

In this study, a dual-spark ignition system was systemically evaluated in a single-cylinder engine. Since the test engine was originally based on the diesel engine, two sparks were located symmetrically on the left and right, with the diesel injector in the middle of the engine head. At first, the effect of dual-spark ignition on the combustion process was compared with the single-spark (only right used) condition under 1600 rpm/gIMEP 0.7 MPa. Also, varying excessive air ratios were evaluated for the two conditions. The second experiment changed the piston bowl shape from (a Mexican) hat to a flat (bathtub-shaped) for the dual-spark ignition system under five representative operating conditions. Also, the maximum load was verified under a knocking frequency of 30%. The results emphasized that dual-spark ignition showed superb CoV of net indicated mean effective pressure (nIMEP) as 2.71% under excessive air ratio 1.55 condition, while it was higher than 5% with single-spark ignition. In addition, the net indicated thermal efficiency was 37.33%. Also, when flat bowl-shaped piston was used with dual-spark ignition system, the maximum load with avoidance of severe knocking could be increased from nIMEP 1.07 to 1.44 MPa due to enhancing flame propagation speed.