Effect of start of injection on the combustion characteristics in a heavy duty DI engine running on methanol

Paper #:
  • 2017-01-0560

Published:
  • 2017-03-28
Abstract:
Methanol as an alternative fuel in internal combustion engines has an advantage in decreasing emissions of greenhouse gases and soot. Hence, developing a high performance internal combustion engine operating with methanol has attracted the attention in industry and academic research community. This paper presents a joint experimental and numerical study of methanol combustion in a direct injection compression ignition engine. The aim is to investigate the combustion behavior of methanol when injected at close to top-dead-center (TDC) conditions. The experimental engine is a modified version of a metal heavy duty D13 Scania engine. URANS simulations are performed for various injection conditions. The simulations are based on a relatively detailed chemical kinetic mechanism and a well-stirred reactor (WSR) approach accelerated using a so-called chemistry coordinate mapping (CCM) in a dynamic moving sector engine mesh. The injection of the fuel is treated with Lagrangian particle tracking (LPT) method. The start of injection (SOI) sweep is varied to investigate the transition of combustion mode from HCCI to partially premixed charge (PPC) in order to analyze various characteristics of combustion for methanol. A baseline experimental condition was chosen to validate the model and a good agreement between the experiments and the simulations is found after adjustment of the initial temperature condition. In all injection conditions the combustion phasing is kept the same, i.e. with the 50% heat release at the same crank angle (CA50) by adjusting the intake temperature. It is shown that as SOI is delayed and combustion mode changes from HCCI to PPC, the combustion duration decreases as SOI is delayed, along with an increased pressure-rise-rate (PRR) and heat release rate (HRR). This is contrary to the combustion behavior of diesel and gasoline fuels. Such behavior is attributed to the longer ignition delay time, larger latent heat and lower stoichiometric mixture fraction for methanol than hydrocarbon fossil fuels. It is found that it is rather difficult to achieve PPC mode of methanol combustion with a single injection operation.
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