There are many NO x removal technologies: exhaust gas recirculation (EGR), selective catalytic reduction (SCR), selective non-catalytic reduction (SNCR), miller cycle, emulsion technology and engine performance optimization. In this work, a numerical simulation investigation was conducted to explore the possibility of an alternative approach: direct aqueous urea solution injection on the reduction of NO x emissions of a biodiesel fueled diesel engine. Simulation was performed using the 3D CFD simulation software KIVA4 coupled with CHEMKIN II code for pure biodiesel combustion under realistic engine operating conditions of 2400 rpm and 100% load. To improve the overall prediction accuracy, the Kelvin-Helmholtz and Rayleigh-Taylor (KH-RT) spray break up model was implemented in the KIVA code to replace the original Taylor Analogy Breakup (TAB) model for the primary and secondary fuel breakup processes modeling. The KIVA4 code was further modified to accommodate multiple injections, different fuel types and different injection orientations. A skeletal reaction mechanism for biodiesel + urea was developed which consists of 95 species and 498 elementary reactions. The chemical behaviors of the NO x formation and Urea/NO x interaction processes were modeled by a modified extended Zeldovich mechanism and Urea/NO x interaction sub-mechanism. Developed mechanism was first validated against the experimental results conducted on a light duty 2KD FTV Toyota car engine fueled by pure biodiesel in terms of in-cylinder pressure, heat release rate. To ensure an efficient NO x reduction process, various aqueous urea injection strategies in terms of post injection timing and injection rate were carefully examined. The simulation results revealed that among all the four post injection timings (10 °ATDC, 15 °ATDC, 20 °ATDC and 25 °ATDC) that were evaluated, 15 °ATDC post injection timing consistently demonstrated a lower NO emission level. In addition, both the urea/water ratio and aqueous urea injection rate demonstrated important roles which affected the thermal decomposition of urea into ammonia and the subsequent NO x removal process, and it was suggested that 50% urea mass fraction and 40% injection rate presented the lowest NO x emission levels.

Satisfying the coming International Marine Organization (IMO) NOx emissions requirements and regulations is the main focus of attention in marine engine design. Miller cycle, which reduces in-cylinder combustion temperature by reducing effective compression ratio, is the main measure to reduce NOx specific emissions on the cost of volumetric efficiency and engine power. Therefore, it is essential to combine Miller cycle with highly boosted turbocharging system, for example, two stage turbocharing, to recover the power. In this paper, different two stage turbocharging system scenarios are introduced and compared. The system design and matching process is presented. A multi-zone combustion model based one dimensional cycle simulation model is established. The intake valve closure timing and the intake exhaust valves overlap duration are optimized according to the IMO NOx emission limits by the simulation model. The high and low stage turbochargers are selected by an iterative matching method. Then the control strategies of the boost air and the high stage turbine bypass valves are also studied. As an example, a Miller cycle-regulatable two stage turbocharging system is designed for a type of highly boosted high speed marine diesel engine. The results show that the NOx emissions can be reduced 30% and break specific fuel consumption can also be improved by means of moderate Miller cycle combined with regulatable two stage turbocharing.

The relative benefit of a power turbine as a means of exhaust energy recovery (i.e., turbocompounding) being used in conjunction with altered intake valve closure timing (Miller cycle) on a medium speed diesel engine has been investigated. An assessment of the impact of these different engine architectures on the various loss mechanisms has been performed using second law analysis. The Miller and turbocompounding cycle modification as well as the combination of the two features were studied and their relative benefits are compared and discussed. Results show the corresponding decrease in effective compression ratio achieved with Miller cycle leads to lower pre-turbine exhaust availability, which decreases the potential benefit of turbocompounding.

The purpose of this study is to determine the optimum intake valve closing time of a large diesel engine having lower fuel consumption and lower NOx emission. The performance simulation has been conducted for this purpose, and a phenomenological combustion model is verified by experimental data of heat release rate and NOx emission in order to enhance the prediction quality of the performance simulation. The results of performance simulation are compared with measured data to confirm the modeling method and results. The fuel injection system simulation has been also performed to get fuel injection rate, and the results is also verified by experimental data of fuel injection pump pressure and injected fuel mass. The performance simulation investigate the application of Miller cycle to a large diesel engine, and so, the intake valve closing time is determined at the condition of reducing NOx emission and fuel consumption at the same time. As that result, Miller cycle has a feature that the maximum reduction of NOx emission is 15.7% while the improvement of specific fuel oil consumption is 1.7g/kWh.

An experimental investigation of NOx emission reduction from automotive (petrol) engine using the Miller Cycle was carried out. Two versions of Miller Cycle were designed and realized on a petrol engine. The tests were carried out on the test rig. The test results showed that applying Miller Cycle could reduce the emission of nitrogen oxides from petrol engine.

The Entropy Generation Minimization (EGM) method is based on the analysis by three sciences (thermodynamics, fluid flow and heat transfer) of the different processes that may occur in a system or in an equipment. Herein the EGM method is applied to internal combustion engines to determine the entropy generation caused by different processes. A model incorporating entropy generation calculations is used to assess various engines configurations. Otto cycle was tested and Variable Valve Timing (VVT) and Variable Compression Ratio (VCR) were applied so thermodynamic benefits could be tested and evaluated. With the referred model, the Miller cycle variables are analyzed in order to establish the best working conditions of an engine under a certain load. The intake and exhaust valve timing, combustion start, compression ratio adjustment and heat transfer are the variables for which a best working condition is determined based on the minimization of the entropy generation of the several engine processes.