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The performance of two spray models for predicting liquid and vapor fuel distribution, combustion and emissions is investigated. The model predictions are compared with extensive data from in-cylinder laser diagnostics carried out in an optically accessible heavy-duty, D. I. diesel engine over a wide range of operating conditions. Top-dead-center temperature and density were varied between 800 K and 1100 K and 11.1 and 33.2 kg/m3, respectively. Two spray breakup mechanisms were considered: due to Kelvin-Helmholtz (KH) instabilities and to Rayleigh-Taylor (RT) instabilities. Comparisons of a wide range of parameters, which include in-cylinder pressure, apparent heat release rate, liquid fuel penetration, vapor distribution and soot distribution, have shown that a combination of the KH and the RT mechanisms gives realistic predictions. In particular, the limited liquid fuel penetration observed experimentally was captured by including these two competing mechanisms in the spray model. Furthermore, the penetration of the vapor fuel ahead of the liquid spray was also captured. A region of high soot concentration at the spray tip was observed experimentally and also predicted by the KH-RT spray breakup model. [S0742-4795(00)01504-0]

A multi-dimensional code has been developed to study the effects of injection pressure and nozzle hole inlet conditions on diesel engine performance and emissions. The code includes a new liquid core and spray breakup model. The models were validated using spray visualization images obtained from a single-cylinder version of the Caterpillar 3406 heavy-duty truck engine instrumented with an endoscope system. The computational results were also compared with experimental emissions data. The results show that combustion and emissions predictions are controlled by the details of the spray model. With modifications to the spray model to account for Rayleigh-Taylor and Kelvin-Helmholtz drop breakup mechanisms, the predicted liquid and vapor-fuel penetration agrees well with that measured. The models were applied over a wide range of engine operating conditions and were found to provide good prediction accuracy. The simulations also showed that sharp edged-inlet nozzles give significantly lower particul...

An endoscope-based image acquisition-and-processing camera system was used for diagnostics of pilot injection combustion in a single-cylinder heavy duty diesel engine. A study of the pilot injection or light load is of interest because the spray breakup, mixing and vaporization processes are less influenced by heat feedback from the flame than in full injection cases. This allows the spray process to be decoupled from the combustion process. The experimental cases were modeled using a version of the KIVA-II code that includes improvements in the turbulence, wall heat transfer, spray, ignition and combustion models. The combustion of the pilot injections was characterized by ignition sites located below the point where the spray impinges on the piston bowl surface for the injector configuration used in this study. Multiple ignition sites were observed and the majority of the combustion occurred at the bottom of the piston bowl, spreading along the bowl edge. As the start-of-injection timing was retarded some evidence of ignition above the impingement point was observed. However, these ignition sites did not develop into major combustion zones. Comparisons of the experimental results, which included pressure traces, heat release rates and the luminous flame images, and the numerical computations were made tomore » assess the performance of current models in the KIVA-II code. Good agreement was obtained for the timing and location of ignition. The penetration of the flame observed in the luminous flame images was also captured in the predictions. A feature of the pilot injection that was not captured by the prediction is the spread of the flame along the edge of the piston bowl. The comparisons indicate that recent improvements in KIVA-II allow better prediction of the combustion of pilot injections.« less

Progress on the development and validation of a CFD model for diesel engine combustion and flow is described. A modified version of the KIVA code is used for the computations, with improved submodels for liquid breakup, drop distortion and drag, spray/wall impingement with rebounding, sliding and breaking-up drops, wall heat transfer with unsteadiness and compressibility, multistep kinetics ignition and laminar-turbulent characteristic time combustion models, Zeldovich NOx formation, and soot formation with Nagle Strickland-Constable oxidation. The code also considers piston-cylinder-liner crevice flows and allows computations of the intake flow process in the realistic engine geometry with two moving intake valves. Significant progress has been made using a modified RNG {kappa}-{var_epsilon} turbulence model, and a multicomponent fuel vaporization model and a flamelet combustion model have been implemented. Model validation experiments have been performed using a single-cylinder heavy duty truck engine that features state-of-the-art high pressure electronic fuel injection and emissions instrumentation. In addition to cylinder pressure, heat release, and emissions measurements, new combustion visualization experiments have also been performed using an endoscope system that takes the place of one of the exhaust valves. Modifications to the engine geometry for optical access were minimal, thus ensuring that the results represent the actual engine.more » The intake flow CFD modeling results show that the details of the intake flow process influence the engine performance. Comparisons with the measured engine cylinder pressure, heat release, soot and NOx emission data, and the combustion visualization flame images show that the CFD model results are generally in good agreement with the experiments. In particular, the model is able to correctly predict the soot-NOx trade-off trend as a function of injection timing. 44 refs., 21 figs., 6 tabs.« less