Haiyan Miao

Reduction of Heavy Duty Diesel Engine Emission and Fuel Economy with Multi-Objective Genetic Algorithm and Phenomenological Model

In this study, a system to perform a parameter search of heavy-duty diesel engines is proposed. Recently, it has become essential to use design methodologies including computer simulations for diesel engines that have small amounts of NOx and SOOT while maintaining reasonable fuel economy. For this purpose, multi-objective optimization techniques should be used. Multi-objective optimization problems have several types of objectives and they should be minimized or maximized at the same time. There is often a trade-off relationship between objects and derivation of the Pareto optimum solutions that express the relationship between the objects is one of the goals in this case. The proposed system consists of a multiobjective genetic algorithm (MOGA) and phenomenological model. MOGA has strong search capability for Pareto optimum solutions. However, MOGA requires a large number of iterations. Therefore, for MOGA, a diesel combustion simulator that can express combustion precisely with small calculation cost is essential. Phenomenological models can simulate diesel engine combustions precisely with small calculation cost. Therefore, phenomenological models are suitable for MOGA. In the optimization simulations, fuel injection shape, boost pressure, EGR rate, start angle of injection, duration angle of injection, and swirl ration were chosen as design variables. The values of these design variables were optimized to reduce SFC, NOx, and SOOT. Through the optimization simulations, the following five points were made clarified. First, the proposed system can find the Pareto optimum solutions successfully. Second, MOGAs are very effective to derive the solutions. Third, phenomenological models are very suitable for MOGAs, as they can perform precise simulations with small calculation cost. Fourth, multi-pulse injection shape can affect the amounts of SFC, NOx, and SOOT. Finally, parameter optimization is essential for in diesel engine design.

NUMERICAL SIMULATION OF THE GAS/DIESEL DUAL-FUEL ENGINE IN-CYLINDER COMBUSTION PROCESS

ABSTRACT An alternative fuel such as natural gas may be used in a dual-fuel engine for both economic reasons and emission advantages. However, the performance at relatively light load and idling conditions has been quite poor, while at very high load, engine knock is often encountered. In this study, a three-dimensional, dual-fuel, in-cylinder model has now been developed. This is used to provide an improved understanding of the operational features arising from the interaction between the gaseous fuel and the pilot fuel, the preignition processes, and subsequent combustion of the pilot fuel and gas during the piston movement.

Sensor Placement and Measurement of Wind for Water Quality Studies in Urban Reservoirs

We collaborate with environmental scientists to study the hydrodynamics and water quality in an urban district, where the surface wind distribution is an essential input but undergoes high spatial and temporal variations due to the complex urban landform created by surrounding buildings. In this work, we study an optimal sensor placement scheme to measure the wind distribution over a large urban reservoir with a limited number of wind sensors. Unlike existing sensor placement solutions that assume Gaussian process of target phenomena, this study measures the wind which inherently exhibits strong non-Gaussian yearly distribution. By leveraging the local monsoon characteristics of wind, we segment a year into different monsoon seasons which follow a unique distribution respectively. We also use computational fluid dynamics to learn the spatial correlation of wind in the presence of surrounding buildings. The output of sensor placement is a set of the most informative locations to deploy the wind sensors, based on the readings of which we can accurately predict the wind over the entire reservoir surface in real time. 10 wind sensors are finally deployed around or on the water surface of an urban reservoir. The in-field measurement results of more than 3 months suggest that the proposed sensor placement and spatial prediction approach provides accurate wind measurement which outperforms the state-of-the-art Gaussian model based or interpolation based approaches.

Combustion and particulate emission characteristics of a diesel engine fuelled with diesel-dimethoxymethane blends

Abstract The effect of fuel constituents on the combustion and particle emission characteristics of a compression ignition engine fuelled with diesel—dimethoxymethane (DMM) blends is investigated experimentally. Four engine loads at the maximum torque engine speed of 1600r/min and rated engine speed of 2200r/min were carried out respectively. Three diesel—DMM blended fuels containing 15 vol %, 30 vol %, and 50 vol % DMM, corresponding to 6.35 mass %, 12.67 mass %, and 21.11 mass % oxygen in the blends were used. The study showed that the ignition delay experienced a slight increase while the rapid combustion duration and the total combustion duration decreased with increase in the DMM fraction in the fuel blends. The maximum cylinder pressure, the maximum rate of pressure rise, and the maximum rate of heat release increase with the addition of DMM to the blended fuels. Moreover, the smoke concentration decreases with increase in the oxygen mass fraction in the blends and the reduction rate reaches 80 per cent for 50 vol % DMM in the blend under a high engine load. The influence of DMM on the nanoparticulate distribution was also studied in the tests and it was found that the total number of nanosized particulates are all reduced with increase in the oxygen content in the blends.

Optical Techniques for Diesel Spray and Combustion

Optical techniques play an important role in understanding the diesel spray and combustion to obtain high engine performance and low emissions. Combustion in a diesel engine is closely related to the transient injection of diesel spray into high pressure and temperature air. The air fuel mixing process, including atomisation and vaporization, is followed by the ignition and progressive, diffusive burning of the remaining regions. Diesel combustion is primarily controlled by the mixing process. The quality and distribution of fuel-air mixture are controlled by the characteristics of injection system, the nature of swirl and turbulence in cylinder, and spray characterization, such as spray tip penetration and drop diameter. Effective diagnostics of those phenomena are vital for an improved understanding on them thereby leading to a good control. This paper reviews optical techniques for diesel spray and combustion that were carried out in our laboratory. It starts with the three-dimensional visual measurements of diesel spray and combustion in optical engines. Then measurements of the diesel spray structure, such as spray tip penetration, drop size distribution and drop diameter are discussed. Finally, simultaneous measurements of vapour and liquid concentrations in an evaporating spray by five different optical techniques are introduced.

Ultra-low-emission diesel engine fuelled with dimethoxymethane—diesel fuel blends

Abstract The influences of dimethoxymethane (DMM content), exhaust gas recirculation (EGR) and post-processor on combustion and emission were studied experimentally, and the approaches to meet the Euro III regulation were discussed. Results showed that, for diesel blending fuel with 50 per cent DMM volume fraction, on setting the EGR rate at 28 per cent for low and medium loads and at 7 per cent at high loads, nitrogen oxide and soot emissions are both reduced markedly; a diesel oxidation catalyst (DOC) reduces hydrocarbon and carbon monoxide emissions. Comparison of the combustion process with diesel fuel indicated that application of DMM—diesel blended fuel increases both premixed and diffusion combustion, leading to a higher peak pressure and a pressure rise. EGR does not lengthen the combustion duration significantly. A naturally aspirated diesel engine in the test fuelled with a high percentage of DMM component in the blend, together with EGR and DOC, makes it possible to meet the Euro III emission standard for a vehicle diesel engine.