Summary: An investigation has been made of the effectiveness of water injection into the combustion end zone of a spark-ignition engine cylinder for the suppression of knock. Pressure-time recoreds obtained show that injection of water at 60° B.T.C. on the compression stroke at a water-fuel ratio of 0.3 rendered M-3 fuel as good as S-3 fuel from an antiknock consideration. The optimum crank angle for injection of water into the end zone was found to be critical. As the injection angle was increased beyond the optimum, the quantity of water required to suppress knock increased to 3.6 water-fuel ratio at 132° B.T.C. The water quantity could not be increased beyond 3.6 water-fuel ration because of injection-pump limitations; however, a further increase in the injection angle up to the earliest angle obtainable, which was 20° A.T.C. on the intake stroke, continuously increased the knock intensity. The engine operating conditions of the tests did not simulate those encountered in flight, especially with regard to the operating speed of 570 rpm. For this reason the results should only be regarded as of theoretical importance until further investigation has been made.

Abstract : One of the limiting factors influencing the improvement of engine efficiency in gasoline engines is engine knock. Several techniques including reduced compression ratio, cooled exhaust gas recirculation, using high premium fuels, late intake valve closing have been used to mitigate knock at different operating regimes. Water due to its higher latent heat of vaporization compared to gasoline fuel has been used to reduce the charge temperature and mitigate knock. When water is injected into the intake manifold or into the cylinder, it evaporates by exchanging energy from the surrounding mixture resulting in charge cooling. This allows the engine to be run with advanced spark timing without engine knock resulting in better engine performance. With this motive, the impact of water injection on the combustion characteristics of gasoline direct injection engine was investigated. The research was conducted in three parts. First, an analytical model was developed using the principles of thermodynamics to determine the impact of direct water injection on the cycle efficiency. An ideal thermodynamic cycle with constant volume heat addition was considered for the analysis consisting of air, fuel and water mixture. State properties of the mixture were determined at different points in the thermodynamic cycle and efficiency was calculated. This established a baseline on the amount of water that can be injected into the cylinder and its impact on the overall cycle efficiency. This was followed by spray studies on a spray and combustion vessel that were conducted at engine conditions by varying the ambient conditions to determine the vaporization of water and water methanol sprays. This study gives a comparison of the amount of water that can be vaporized from the thermodynamic model. Experimental studies were conducted on a single cylinder engine with a compression ratio of 10.9:1. Baseline tests without water injection were run using gasoline fuel blended with 10% Ethanol (E10) (Anti-Knock Index = 87.0) injected directly into the cylinder. Impact of water injection was studied by injecting water and blends of water and methanol in the intake manifold at different water fuel ratios within controlled knock limit. Furthermore, injection mechanism was changed to direct water injection and tests were conducted at the same conditions to compare the effect of water injection mechanism on the combustion and knock performance.

Abstract : Dilute combustion is an effective way to increase part-load efficiencies in a Spark Ignition (SI) engine. However, dilute combustion leads to a slower combustion rate and longer burn durations, which results in higher heat transfer loss. To overcome this, some degree of charge flow enhancement exists in modern engines that improves combustion rate and shortens burn durations. This flow enhancement has an adverse effect on performance of the modern Transistorized Coil Ignition (TCI) system and hence presents a limitation on improving combustion rates. Additionally, dilute combustion has a detrimental effect on combustion stability, wherein a larger variation in engine cycle work is observed from cycle to cycle which degrades engine performance. Improving combustion stability under dilution poses a challenge for the modern single coil ignition system, which is where the motivation lies in this research. This research details the development and instrumentation of a Configurable Dual Coil Ignition (CDCI) system that is later tested on a single cylinder metal engine. The effectiveness of different ignition profiles developed with the CDCI system in extending the dilution limit while maintaining combustion performance and lower cycle-cycle variations, thereby improving fuel conversion efficiency, is investigated. Effects of dilution by excess air and internal (exhaust) residuals on the performance of these ignition profiles are investigated under different operating conditions. In-cylinder flow is enhanced by means of tumble planks installed in the intake port of the engine. The impact of enhanced in-cylinder flow on the capabilities of the developed ignition profiles is also investigated under different conditions. Moreover, effects of different spark plug gap sizes and orientations are also investigated. Although majority of the tests are done with Direct Injection (DI) gasoline, some tests are performed with Port Fuel Injection (PFI) methane to compare the effects of fuel delivery and charge preparation.