Estimation of Fueling Variation in Multiple Pulse Injection
Increasingly stringent emission norms have been one of the major driving forces behind the research in diesel engines for more innovative combustion strategies, after-treatment techniques and fuel injection systems. Multiple pulse injection strategies have been investigated to be effective in providing a trade-off to limit the exhaust emissions, noise and fuel consumption. Though multiple injection strategies are advantageous, they are challenging to monitor and control. Multiple injections behave differently in terms of injection parameters such as start of injection (SOI) delay, hydraulic duration and needle velocity which eventually leads to fueling variation for the same rail pressure and commanded on-time values. Thus, estimation and control strategies for single pulse injection are insufficient for multiple injection cases. To compensate for the fueling variation, the first step is to identify or estimate the fueling variation for the given case of multipulse injection. After the first pulse is injected, pressure waves are set up inside the injector body. This changes the initial conditions for the next injection. The current study focuses on the effect of these body pressure fluctuations to estimate the fueling variation in two-pulse cases. A hybrid modeling approach is followed to develop a simple model for the lower body of the injector to estimate the mass flow rate and fueling. The model is calibrated using an optimization technique to compute a set of coefficients defining the given injector configuration using a set of simulated single pulse injection cases. These coefficients are implemented to estimate the fueling and calculate the fueling variation (i.e. delta fueling) for the second pulse of a two-pulse case by using a simulated body pressure signal. The results of the technique are discussed for a number of rail pressure, commanded on-time and hydraulic separation values. The injectors under study belong to the family of Cummins Scania XPI injectors. These are solenoid actuated, high pressure injectors. The work is sponsored by Cummins Fuel Systems, Columbus, Indiana.
Meckl, Purdue University.
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