Research has shown that a large amount of natural gas (NG) is unburned at light loads in an NG fuelled/micro-pilot diesel compression ignition engine. A mechanism of unburned hydrocarbon (HC) reduction using multiple injections of micro-pilot diesel has been proposed in this paper. Multidimensional computations were carried out for a dual-fuel engine based on a modified CAT3401 engine configuration. The computations show that a split injection with a small percentage (e.g. 30 per cent of diesel in the second injection pulse) can significantly reduce HC, CO and NOx emissions. Based on parametric studies to optimize the timing of both of the injection pulses, HC emissions could be reduced by 90 per cent, with a reduction in CO emissions of 50 per cent and NOx emissions of 70 per cent in comparison to a single-injection pulse-base case configuration.

No abstract

A staged combustor concept for reducing pollutant emissions is currently under investigation. A numerical study was performed to investigate the chemically reactive flow with liquid spray injection for staged combustion. The staged combustor consists of an airblast atomizer fuel injector, a rich burn section, a converging connecting pipe, a quick mix zone, a diverging connecting pipe and a lean combustion zone. For computational efficiency, the combustor was split into two subsystems, i.e., the fuel nozzle/rich burn section and the quick mix/lean burn section. The current study investigates the effect of varying the mass flow rate split between the swirler passages for an equivalence ratio of 2.0 on fuel distribution, temperature distribution, and emissions for the fuel nozzle/rich burn section of a staged combustor. It is seen that optimizing these parameters can substantially improve combustor performance and reduce combustor emissions. The optimal mass flow rate split for reducing NOx emissions based on the numerical study was the same as found by experiment.

No abstract

A three-dimensional unsteady turbulent compressible Navier-Stokes solver, KIVA3V, was utilized in the present study to investigate the intake and in-cylinder flowfield of a four-valve direct injection compression ignition engine. Successful modelling of internal combustion engine configurations is highly dependent upon the generation of a quality grid with the correct boundary conditions. The preprocessor of the KIVA3V computer code, K3PREP, was improved, and a complete grid for a four-valve/cylinder single-cylinder caterpillar diesel test engine, CAT3401, was generated. The complete grid consisted of four moving valves, two intake ports, two exhaust ports, and the port runners. Predicted global in-cylinder flow quantities were compared against experimental data. It was found that the intake process was well modelled by KIVA3V with this complete grid. It was also found that important complex flow structures are developed during the intake stroke. While many of these structures decay during the compression stroke, swirl and tumble can survive. The effect of increased swirl ratio at the end of the compression stroke for the CAT3401 engine with a piston bowl is clearly observed in this study. This is important for aiding in good fuel spray atomization. The formation, development, and break-up of tumble flow are seen, contributing to an increase in turbulent kinetic energy at the end of the compression stroke. Other researchers have substantiated this phenomenon for this type of engine flow. The complete engine flowfield, i.e. the inlet jet, pressure variation in the intake runner and ports, and formation of swirl in the intake ports, is also clearly shown in the prediction. The homogeneity of the in-cylinder flow characteristics and temperature field is also studied. Results of these simulations aid in the improved understanding of the intake process and its influence on direct injection compression ignition engine flowfields.

No abstract

A multistage combustion model for diesel engines is presented in this paper. Three combustion stages, ignition of diesel, premixed combustion and diVusion combustion, are considered in the combustion process in a typical medium speed direct injection diesel engine. The transition from the ignition delay to the premixed combustion stage occurs when the highest temperature in the cylinder is beyond a critical value, and the transition from the premixed combustion model to the diVusion combustion model occurs when a calculated fraction of the premixed fuel is burned, which is determined from an empirical correlation based on the engine design and running conditions. Signi cant improvements in the predictions for in-cylinder pressure and heat release rate were achieved compared with previous models. A soot model based on the Hiroyasu soot formation mechanism and the Nagle and Strickland-Constable soot oxidation mechanism was implemented in a standard KIVA3V code. The eVect of the OH radical in soot oxidation was also incorporated into the soot model. Computations show that OH plays an important role during the late combustion stage. Predicted soot and NO x were compared with measured values and a good agreement was achieved.

No abstract