Investigation of Combustion Noise Development with Variation in Start of Injection using 3-Dimensional Simulations by Applying Representative Interactive Flamelet (RIF) Model

Engine noise pollution is as harmful as other forms of pollution to human health. Apart from the health effects, noise also has an adverse effect on the engine structure, thus requiring a sturdier construction to maintain long engine life. In a conventional direct injection diesel engine the fuel ignites spontaneously shortly after the beginning of injection. The Combustion process causes fluctuations in heat release and therefore, fluctuations in combustion chamber pressure. Combustion generated noise can be lowered by lowering the fluctuations in heat release or pressure. Which can be achieved by separating the fuel evaporation and fuel-air mixing from start of ignition in space and in time. The noise is mainly affected by the early part of the combustion process due to higher rates of heat release. Combustion noise generation in the early stage of combustion is not yet entirely understood. Three-dimensional numerical simulations can be helpful to address this problem and to identify the parameters involved in the generation of combustion noise.

In the present work experiments and simulations were performed for different start of injection (SOI) to investigate the effect of mixture formation on combustion generated noise. The experiments were done on a 1.9 Liter four cylinder direct injection GM-FIAT diesel engine using European diesel fuel. Representative Interactive flamelet model (RIF) was applied for the numerical simulations. RIF model uses a CFD code coupled interactively with the flamelet model. The diesel fuel for simulations is substituted by a two-component surrogate fuel which is a mixture of 70% n-decane and 30% α-methylnaphthalene (by liquid volume fraction) and is known as IDEA fuel. The chemical reaction mechanism consists of 506 elementary reactions and 118 chemical species. The simulated results using RIF are in good agreements with the experimental results. Ringing intensity correlation was used as a quantitative indicator of combustion noise for the experiments and simulations. Additionally, an approach based on unsteady flamelet temperature solutions in mixture fraction space is proposed to investigate combustion noise. This method provided a deeper understanding of noise generation.