Search Results

The addition of exhaust gas recirculation (EGR) has demonstrated the potential to significantly improve engine efficiency by allowing high CR operation due to a reduction in knock tendency, heat transfer, and pumping losses. In addition, EGR also reduces the engine-out emission of nitrogen oxides, particulates, and carbon monoxide while further improving efficiency at stoichiometric air/fuel ratios. However, improvements in efficiency through enhanced combustion phasing at high compression ratios can result in a significant increase in cylinder pressure. As cylinder pressure and temperature are both important parameters for estimating the durability requirements of the engine - in effect specifying the material and engineering required for the head and block - the impact of EGR on surface temperatures, when combined with the cylinder pressure data, will provide an important understanding of the design requirements for future cylinder heads.

Two constant-volume combustion chambers and a 2.3L SI engine were used to investigate the effects of spark plug electrode configurations on flame kernel formation and development, and on engine performance. The results showed performance differences between the spark plug types tested in terms of lean ignitability limit and 0-2% MFB time. Overall, the spark plugs with 0.6 mm diameter center electrode, referred to as Finewire spark plugs, were able to ignite the leanest mixtures and were the only spark plug type to demonstrate the lowest predicted 0-2% MFB times for both 0% and 20% EGR. The Schlieren images support the results of better ignitability confirming the fastest flame kernel development with Finewire spark plugs and demonstrating the benefits of J-gap design and fine center electrode. The results explain significant advantages in engine performance in terms of engine stability and fuel consumption rate.

Engine tests were conducted on a production 2.5-liter V-6 engine to investigate the effects of spark plug tip designs on a 4-cycle SI engine of current technology. The data suggest that cyclic variation can increase when the ground electrode faces the primary intake port. Lean-operation limits were extended by the use of J-gap spark plugs as compared to surface-gap and ring-gap spark plugs at the conditions tested. The surface-gap type spark plugs lose some energy as the arc traverses the surface of the insulator. Voltage requirements decrease for reversed polarity at the part load conditions tested but increase at wide open throttle.