Optimization of EGR Mixer to Minimize Thermal Hot Spot on Plastic Duct Soot Deposition on Throttle Valve Using CFD Simulation

摘要

In recent time, with inception of BS VI emission regulation with more focus on fuel economy and emission, many engine parts which were conventionally made from metal are getting replaced with plastic components for reducing weight to attain better fuel economy. EGR is commonly used technique to reduce emissions in diesel engine along with after treatment devices. EGR reduces peak combustion temperature inside the combustion chamber thereby reducing NO_x. EGR is bypassed from the exhaust manifold, cooled down in EGR cooler and mixed with intake air at upstream of the intake manifold. Throttle valve is used for controlling the charged air flow to cylinders for different vehicle operating conditions. With compact engine layout EGR mixer are often located near to throttle valve thereby increasing the possibility of soot deposition on throttle valve. Once these soot & hydrocarbons cool down they can transform into sticky amorphous carbon, which obstruct the functioning of throttle valve thereby leads to not meeting the required emission levels. At the same time, hot EGR impinging on plastic intake ducts can melt the plastic surface. Mixer module is provided to create turbulence for better mixing of EGR & fresh air. While most of the literature work done in past is based on EGR distribution analysis, this paper focuses on minimizing the thermal hotspot and chances of soot deposition on throttle valve along with cylinder-to-cylinder EGR distribution. It was challenging to design an EGR mixer with given constraints which could meet all the above requirements. The boundary conditions for the highly pulsating flow are used from transient 1-D simulation. CFD simulations are performed for different EGR mixers to evaluate & reduce temperature on the plastic duct, soot deposition and increase EGR mixing quality. For the final model, hot spot location, soot deposition and cylinder-to-cylinder distribution were optimized.