Effects of pre-turbocharger turbine water injection on the performance of spark-ignition engine

Abstract

Following the stringent emission legislation in the major automotive markets, the downsized boosted engine becomes the engine design trend that almost all automakers have been adopted. A turbocharged engine has the disadvantages of high exhaust gas temperature at medium to high engine load and engine speed operations. Fuel enrichment is the common strategy used to control the high exhaust temperature within the permissible thermal limit of the catalytic converter and turbine vane. Water injection strategies have been proven to be a promising technique to improve the performance of boosted engine while reducing the NOx emission via the latent heat of vaporization of water. Plenty of water injection research was conducted on in-cylinder and intake port water injection. However, the water injection research on the spark ignition engine exhaust system section is still lacking. This research proposed a preturbocharger turbine water injection concept to reduce the turbine inlet temperature. In turn, the stoichiometric engine operation could be achieved at the medium-high load and speed engine operation without resorting to fuel enrichment strategy in reducing the exhaust gas temperature. The purpose of this study was to investigate the effect of injecting water into the exhaust gas at the pre-turbine of a turbocharged spark-ignition engine. This study was initiated by experimenting using a 1.3-litre 4-cylinder turbocharged engine on a test bench to collect engine data for Computational Fluid Dynamics (CFD) baseline model validation. Simultaneously, a one-dimensional engine model was then developed based on the 1.6-litre 4-cylinder turbocharged engine experiment using AVL BOOST software. The CFD model was used to investigate the effects of water injection pressure, pipe diameter and water injector location. The CFD results showed that a 50 mm connecting pipe with 4 bar of injection pressure gives the most exhaust temperature drops. The CFD results were then applied to the one-dimensional engine model. The engine model simulation results showed that the fuel consumption can be reduced up to 13% at 4,000 rpm during wide-open throttle and 75% engine load. This research proved the potential of using water injection at the pre-turbine turbocharger to reduce the fuel consumption of a turbocharged spark-ignition engine. The pre-turbocharger turbine water injection is a new approach, requiring further optimisations and improvements to fulfil the market demand for a fuel-efficient vehicle with stringent emission regulations.