Efficient Approach for Optimization of Piston Bowl Shape, Compression Ratio and EGR for DI Diesel Engine 2011-24-0013

In order to meet emission norms, modern day diesel engines rely on methods of in cylinder emission reduction and expensive exhaust after treatment devices. Engine manufacturers across the world are finding it hard to maintain balance between customers' demand for better fuel consumption and obeying the stringent legislative emission regulations. Optimum combination of variables such as piston bowl shape, compression ratio, fuel injection and turbo charging systems precisely matched with engine, Exhaust Gas Re-circulation (EGR) rate etc can result in refined combustion leading to better engine out emissions as well as fuel efficiency.

Optimization of piston bowl geometry and EGR rate would require a lot of experiments, which involves cost and time. If the numbers of variants of piston bowl shapes or EGR rates are more, so would be the expensive and require more testing time. Such approach proves to be inefficient in today's scenario, where minimizing the development time and expenses are the key objectives. In the present work, a approach based on 3D CFD simulation for optimization of piston bowl together with EGR rate is presented. Multidimensional CFD code “Engine Simulation Environment” i.e “ESE Diesel” of AVL-FIRE is used to run the simulations. The model is first validated with available engine measurements and then used for the optimization work. Three different shapes of piston bowl were selected for simulation. Combustion simulation was carried out to select optimum bowl shape. With the optimum bowl shape, simulation iterations were performed by varying EGR rate from 0 to 20%. NOx & exhaust soot trends are compared for different simulation model. Optimum bowl shape and EGR rate were decided based on the targets for specific fuel consumption, exhaust emissions, percentage of soot etc. Final combination of piston bowl shape and EGR rate was actually tested on engine. Test results in close conformity with simulation results were observed.

A significant reduction in number of test experiments and the associated time and cost was experienced by following this simulation centric approach.