The effects of boost pressure on stratification and burn duration of gasoline homogeneous charge compression ignition combustion

Abstract

This article investigates the effects of intake pressure (boost) on the pre-ignition stratification and burn duration of homogeneous charge compression ignition combustion. Full cycle computational fluid dynamics simulations are performed with gasoline kinetics. An intake pressure sweep is performed while maintaining the same combustion timing and mean composition. The burn duration reduces with increasing boost, even though intake temperature is reduced to hold combustion timing constant. It is shown that the compositional stratification increases with boost whereas thermal stratification decreases. A quasi-dimensional model is employed to assess the effect of compositional stratification, pressure, mean temperature and isolate the effect of thermal stratification on burn duration. The analysis reveals that reducing charge temperature neutralizes the effect of increased boost on reactivity and the shorter burn durations at higher boost are primarily due to the lower thermal stratification. It is shown that higher pressures do not significantly increase the mixing and the lower thermal stratification is due to lower wall heat losses per unit charge mass. A follow-up set of non-reacting simulations with adiabatic walls corroborate this claim by revealing a constant magnitude of thermal stratification across the boost sweep.

An applicable approach to mitigate pressure rise rate in an HCCI engine with negative valve overlap

“…Scaringe et al [18] reported the same trend for lean HCCI operation and proved that PRR-limited load range could not be extended with alternative mixture dilution measures, such as EGR. The recent work by Shingne et al [24] uses reactive computational fluid dynamics simulations and quasi-dimensional modelling to attempt to explain why raising intake pressures leads to increased PRR max . The authors prove that high boost reduces the heat (per unit charge mass) transferred to cylinder walls.…”

Physics-based modeling of homogeneous charge compression ignition engines with exhaust throttling

“…The main contribution of this paper is the development of a physics-based single-zone crank-angle-resolved model for an HCCI engine with the cost effective exhaust throttle, which is little explored in the literature. By capturing the gas exchange and combustion processes, the proposed crank-angle-resolved model provides more detailed information than the existing mean value model in Souder et al 35 On the other hand, the proposed single-zone model provides satisfactory prediction of the HCCI combustion phasings with reduced computation cost compared to the existing multi-zone models in Shingne et al, 31 Garcia-Guendulain et al, 32 Wick et al 33 The closed-loop simulation results with the LQG controller shows an application example of the proposed model and the potential of using the cost effective exhaust throttle for regulation of HCCI combustion timings.…”

“…For instance, re-induction can be achieved by reopening the exhaust valve during the intake stroke, hence some of the exhaust gas is reinducted into the cylinder along with the fresh charge. 24,26,27 On the other hand, early closing of the exhaust valve and late opening of the intake valve, also known as negative valve overlap (NVO) [28][29][30][31][32][33] leads to retention of burned charge inside the cylinder. Stability analysis is conducted based on an HCCI engine with high dilution reinducted by a second opening of the exhaust valve during the intake stroke.…”

“…The proposed exhaust throttle mechanism, which is little explored, is cost effective and can easily be installed even on two wheelers. The crank angle resolved model gives the full trace of the cylinder pressure, temperature, and burned gas fraction, hence provides more insight about the gas exchange and combustion process compared to the mean value model in Souder et al 35 On the other hand, compared to the multi-zone models in Shingne et al, 31 Garcia-Guendulain et al, 32 Wick et al, 33 which provide more detailed thermodynamic conditions, the zero-dimensional single zone model is capable of predicting the HCCI combustion timings with reduced computation cost in the real-time hardware-in-the-loop (HIL) simulation environment when uniform distributions of the mixture and temperature are considered. 38 The dynamics of the engine model are exhibited collectively by the evolution of states in the intake, exhaust runners, and the cylinder.…”