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Technical Paper

Development and Application of a Non-Gradient Step-Controlled Search Algorithm for Engine Combustion Optimization

A new search technique, called Non-Gradient Step-Controlled algorithm (NGSC), is presented. The NGSC was applied independently from pre-selected starting points and as a supplement to a Genetic Algorithm (GA) to optimize a HSDI diesel engine using split injection strategies. It is shown that the NGSC handles well the challenges of a complex response surface and factor high-dimensionality, which demonstrates its capability as an efficient and accurate tool to seek “local” convergence on complex surfaces. By directly tracking the change of a merit function, the NGSC places no requirement on response surface continuity / differentiability, and hence is more robust than gradient-dependent search techniques. The directional search mechanism takes factor interactions into consideration, and search step size control is adopted to facilitate search efficiency.
Technical Paper

Application of A Multiple-Step Phenomenological Soot Model to HSDI Diesel Multiple Injection Modeling

Multiple injection strategies have been revealed as an efficient means to reduce diesel engine NOx and soot emissions simultaneously, while maintaining or improving its thermal efficiency. Empirical soot models widely adopted in engine simulations have not been adequately validated to predict soot formation with multiple injections. In this work, a multiple-step phenomenological (MSP) soot model that includes particle inception, surface growth, oxidation, and particle coagulation was revised to better describe the physical processes of soot formation in diesel combustion. It was found that the revised MSP model successfully reproduces measured soot emission dependence on the start-of-injection timing, while the two-step empirical and the original MSP soot models were less accurate. The revised MSP model also predicted reasonable soot and intermediate species spatial profiles within the combustion chamber.
Technical Paper

In-Cylinder Measurement of Particulate Radiant Heat Transfer in a Direct Injection Diesel Engine

A method of determining the total hemispherical in-cylinder radiant heat transfer of a direct injection diesel engine was developed using the Two Color theory. A radiant probe was installed in the head of a single cylinder test engine version of a Cummins N14 diesel engine to facilitate the optical measurement. Two probes, installed one at a time, were used to provide the data to calculate the hemispherical radiant heat flux. Each of the probes had a different field of view but both had a near-hemispherical field of view and used a window material that exhibits a cosine-normalized response. The radiant probes were designed to be self-cleaning and remained free of soot deposits during engine operation at high load. The test engine was operated at 1200 and 1500 RPM and at 50, 75, and 100% load for each engine speed. At each operating combination of engine speed and load, measurements were made at several injection timings.
Technical Paper

Modeling the Effects of Late Cycle Oxygen Enrichment on Diesel Engine Combustion and Emissions

A multidimensional simulation of Auxiliary Gas Injection (AGI) for late cycle oxygen enrichment was exercised to assess the merits of AGI for reducing the emissions of soot from heavy duty diesel engines while not adversely affecting the NOx emissions of the engine. Here, AGI is the controlled enhancement of mixing within the diesel engine combustion chamber by high speed jets of air or another gas. The engine simulated was a Caterpillar 3401 engine. For a particular operating condition of this engine, the simulated soot emissions of the engine were reduced by 80% while not significantly affecting the engine-out NOx emissions compared to the engine operating without AGI. The effects of AGI duration, timing, and orientation are studied to confirm the window of opportunity for realizing lower engine-out soot while not increasing engine out NOx through controlled enhancement of in-cylinder mixing.
Technical Paper

Comparison of Numerical Results and Experimental Data on Emission Production Processes in a Diesel Engine

Simulations of DI Diesel engine combustion have been performed using a modified KIVA-II package with a recently developed phenomenological soot model. The phenomenological soot model includes generic description of fuel pyrolysis, soot particle inception, coagulation, and surface growth and oxidation. The computational results are compared with experimental data from a Cummins N14 single cylinder test engine. Results of the simulations show acceptable agreement with experimental data in terms of cylinder pressure, rate of heat release, and engine-out NOx and soot emissions for a range of fuel injection timings considered. The numerical results are also post-processed to obtain time-resolved soot radiation intensity and compared with the experimental data analyzed using two-color optical pyrometry. The temperature magnitude and KL trends show favorable agreement.