Investigation of the effect of steam injection on performance and emissions in a turbocharged diesel engine running with the Miller cycle

It is known that ship based emissions, particularly NOx emissions, have so many detrimental effects on the environment. MARPOL (International Convention for the Prevention of Pollution from Ships) regulations, which determines the limit values of pollutants released from vessels, is going to reduce the limitations of the NOx emissions originating from marine diesel engines severely, in the near future. Therefore, the development of the control methods which are new and quickly adaptable are required to decrease the levels of the ship sourced NOx emissions. As new methods are developed and applied to the engines, the optimum design and operating conditions must be determined by considering effective power and specific fuel consumption which define economical performance as much as emission levels which describe ecological performance. In this study, the effects of the applications of the Miller cycle based on late intake valve closing technique, electronically controlled steam injection and turbocharging on the performance and NOx emissions of a single-cylinder diesel engine running at full load condition have been experimentally and theoretically investigated. In the section of the theoretical studies, parametrical studies based on thermodynamical analyses, single-zone and two-zone combustion simulations have been carried out. The thermodynamical analyses and performance optimization of the Dual-Miller cycle have been conducted and compared with those of the other gas cycles. Moreover, combustion and heat transfer influences on the cycle performance have been parametrically examined. The optimum steam temperatures and mass ratios have been determined with respect to turbocharging pressures. A new thermodynamical model based on finite time thermodynamics, which is comparable with experimental results, has been developed. Additionally, single-zone and two-zone combustion simulation models have been developed. The effects of the Miller cycle, steam injection and turbocharging on the engine performance and NO emissions could be investigated with these models. In the experimental studies, the performance and emissions for three different cam shafts (for 5,10 and 15 degree, crank angle retard closing), three different steam ratios (10%, 20% and 30%) and three different turbocharging pressures (1.1, 1.2 and 1.3 bar) have been obtained and compared with those of the standard conditions. The theoretical results obtained with the finite time thermodynamical model (FTTM) and combustion simulation model (CSM) have been compared with the experimental data. The results show that a diesel engine operating with Dual-Miller cycle have higher performance than a diesel engine running with Dual-Diesel cycle at the same cycle temperature and pressure ratios. Hereby, Dual-Miller cycle causes to lower combustion temperatures and NOx formation. Moreover, it has been theoretically demonstrated that temperature of injected steam does not lead to condensation in the cylinder. In this study, two-zone combustion model gives closer results to the experimental data compared to single-zone combustion model. Thus, two-zone combustion model has been selected as CSM. The experimental results have been compared with the results of CSM and FTTM. The maximum errors are 10% and 6% for FTTM and CSM, respectively. The best condition has been obtained with camshaft 57 and 30% steam rate in terms of NOx emissions. However, the engine performance has been remarkably reduced. The conditions at the camshaft 57, 20% steam rate and 1.1 bar turbocharging pressure have been found as optimum conditions, when the performance and all emissions are considered together. In these conditions, the maximum reduction rates of NOx, HC, CO, CO2 and specific fuel consumption (SFC) are 46%, 46%, 74%, 8% and 15.3%, respectively. However, the maximum moment increase rate is 22.5%. The results demonstrate that the applications of these methods together in the marine diesel engines operated with constant speeds and stationary power plants will be very useful ecologically and economically.