Thermodynamic model for homogeneous charge compression ignition combustion with recompression valve events and direct injection: Part II—Combustion model and evaluation against transient experiments

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This two-part article presents a model for boosted and moderately stratified homogeneous charge compression ignition combustion for use in thermodynamic engine cycle simulations. The model consists of two components: one an ignition model for the prediction of auto-ignition onset and the other an empirical combustion rate model. This article focuses on the development and validation of the homogeneous charge compression ignition model for use under a broad range of operating conditions. Using computational fluid dynamics simulations of the negative valve overlap valve events typical of homogeneous charge compression ignition operation, it is shown that there is no noticeable reaction progress from low-temperature heat release, and that ignition is within the high-temperature regime (T . 1000 K), starting within the highest temperature cells of the computational fluid dynamics domain. Additional parametric sweeps from the computational fluid dynamics simulations, including sweeps of speed, load, intake manifold pressures and temperature, dilution level and valve and direct injection timings, showed that the assumption of a homogeneous charge (equivalence ratio and residuals) is appropriate for ignition modelling under the conditions studied, considering the strong sensitivity of ignition timing to temperature and its weak compositional dependence. Use of the adiabatic core temperature predicted from the adiabatic core model resulted in temperatures within 61% of the peak temperatures of the computational fluid dynamics domain near the time of ignition. Thus, the adiabatic core temperature can be used within an auto-ignition integral as a simple and effective method for estimating the onset of homogeneous charge compression ignition autoignition. The ignition model is then validated with an experimental 92.6 anti-knock index gasoline-fuelled homogeneous charge compression ignition dataset consisting of 290 data points covering a wide range of operating conditions. The tuned ignition model predictions of u 50 have a root mean square error of 1.7°crank angle and R 2 = 0.63 compared to the experiments.

Section: Ignition Model Tuning and Validationmentioning

confidence: 87%

Section: Engine Experimentsmentioning

confidence: 99%

Section: Cfd Simulation Set-upmentioning

confidence: 99%

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A thermodynamic model for homogeneous charge compression ignition combustion with recompression valve events and direct injection: Part I — Adiabatic core ignition model

Shingne

Middleton

Assanis

et al. 2016

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“…It must be noted that chemistry during NVO is ignored. Shingne 34 has shown that reactions during NVO can change the temperature and composition of the charge. However, Olesky et al 32 show in their experimental study that early combustion phasing, similar to current simulations, lead to high combustion efficiency and little NVO heat release due to unburned fuel.…”

Section: Open-cycle Cfd Simulationsmentioning

confidence: 99%

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

Shingne

Middleton

Borgnakke

et al. 2018

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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.

“…12 Multi-cycle computational fluid dynamics (CFD) models have also been used to show this effect and have determined that the remaining fuel and intermediate species from the previous cycle can lead to combustion during the negative valve overlap (NVO) recompression and an early combustion phasing in the following cycle. 13…”

Section: Introductionmentioning

confidence: 99%

Homogeneous charge compression ignition combustion stability improvement using a rapid ignition system

Gordon

Wouters

Kinoshita

et al. 2020

When compared to traditional engines, homogeneous charge compression ignition has the potential to significantly reduce NO x raw emissions, while maintaining a high fuel efficiency. Homogeneous charge compression ignition is characterized by compression-induced autoignition of a lean homogeneous air–fuel mixture. Since homogeneous charge compression ignition does not utilize direct ignition control, it is strongly dependent on the state of the cylinder charge and can suffer from high cyclic variability. With spark-assisted compression ignition, it has been demonstrated that misfires can be reduced, while preserving the high thermal efficiency of homogeneous charge compression ignition as a result of the more favorable physical mixture properties due to dilution. However, spark-assisted compression ignition reduces the NO x benefits of homogeneous charge compression ignition, as it increases the local combustion temperatures. To merge the advantages of the homogeneous charge compression ignition and the spark-assisted compression ignition combustion processes, a field-programmable gate array for detailed simulation of the physical gas exchange is combined with a rapid spark system. The low latency and computational speed of the field-programmable gate array allows the simulation process to be implemented in real time. When combined with the rapid reaction time of the high-frequency current-based rapid ignition system, a feedforward controller based on the cylinder pressure or heat release is realized. The developed model-based controller determines if a spark is required to assist the homogeneous charge compression ignition combustion process. The use of the field-programmable gate array and rapid ignition system allows for the calculation of combustion properties and controller output within 0.1 °CA. This article presents the development and experimental validation of the developed controller on a single-cylinder research engine. The combustion stability has been significantly improved as reflected in an improved standard deviation of the indicated mean effective pressure and a reduction of the combustion phasing variations. Furthermore, compared to a traditional homogeneous charge compression ignition system, the hydrocarbon emissions can be reduced, while maintaining low NO x emissions.