A hybrid spark ignition/homogeneous charge compression ignition engine model for simulating the spark ignition to homogeneous charge compression ignition transition in a four-cylinder gasoline engine is presented. This hybrid spark ignition/homogeneous charge compression ignition model has been developed to provide help in understanding the complicated spark ignition to homogeneous charge compression ignition transition process and in tackling the control problems associated with it. The model was built in Matlab/Simulink, coupled with a tabulated stochastic reactor model and a detailed chemical kinetics mechanism. Typical computational times encountered in the simulation using this model were of the order of seconds for one engine cycle. The model was validated in steady-state spark ignition and homogeneous charge compression ignition operation by experimental data, followed by model-based parametric studies in homogeneous charge compression ignition operation. Then, a spark ignition to homogeneous charge compression ignition mode transition was simulated using the model. The results showed good agreement with experimental data, in terms of cylinder pressure, combustion phasing, air/fuel ratio, residual gas fraction and nitrogen oxides. The high computational efficiency and relatively high accuracy of this model enable its good applicability in experimental design and controller development, and potential use in hardware-in-loop applications.

An established Stochastic Reactor Model (SRM) is used to simulate the transition from Spark Ignition (SI) to Homogeneous Charge Compression Ignition (HCCI) combustion mode in a four cylinder in-line four-stroke naturally aspirated direct injection SI engine with cam profile switching. The SRM is coupled with GT-Power, a one-dimensional engine simulation tool used for modelling engine breathing during the open valve portion of the engine cycle, enabling multi-cycle simulations. The mode change is achieved by switching the cam profiles and phasing, resulting in a Negative Valve Overlap (NVO), opening the throttle, advancing the spark timing and reducing the fuel mass as well as using a pilot injection. A proven technique for tabulating the model is used to create look-up tables in both SI and HCCI modes. In HCCI mode several tables are required, including tables for the first NVO, transient valve timing NVO, transient valve timing HCCI and steady valve timing HCCI and NVO. This results in the ability to simulate the transition with detailed chemistry in very short computation times. The tables are then used to optimise the transition with the goal of reducing NO x emissions and fluctuations in IMEP. Copyright © 2010 SAE International.

This paper presents experimental results and a new computational model that investigate cycle to cycle variations (CCV) in a spark ignition (SI) engine. An established stochastic reactor model (SRM) previously used to examine homogeneous charge compression ignition (HCCI) combustion has been extended by spark initiation, flame propagation and flame termination sub-models in order to simulate combustion in SI engines. The model contains a detailed chemical mechanism but relatively short computation times are achieved. The flame front is assumed to be spherical and centred at the spark location, and a pent roof and piston bowl geometry are accounted for. The model is validated by simulating the pressure profile and emissions from an iso-octane fuelled single cylinder research engine that showed low CCV. The effects of key parameters are investigated. Experimental results that show cycle to cycle fluctuations in a four-cylinder naturally aspirated gasoline fuelled SI engine are presented. The model is then coupled with GT-Power, a one-dimensional engine simulation tool, which is used to simulate the breathing events during a multi-cycle simulation. This allows an investigation of the cyclic fluctuations in peak pressure. The source and magnitude of nitric oxide (NO) emissions produced by different cycles are then investigated. It was found that faster burning cycles result in increased NO emissions compared with cycles that have a slower rate of combustion and that more is produced in the early stages of combustion compared with later in the cycle. The majority of NO was produced via the thermal mechanism just after combustion begins.

Air/Fuel Ratio (AFR) and Residual Gas Fraction (RGF) are difficult to control during the SI-HCCISI transition, and this may result in incomplete combustion and/or knocking. As a result, engine load may fluctuate, as indicated by the Net Indicated Mean Effective Pressure (NIMEP). The objectives of this work are to further understand this process and develop control methods to minimize the engine load fluctuation. This paper presents instantaneous AFR and RGF measurements, both taken by novel experimental techniques. The data provides an insight into the cyclic AFR and RGF fluctuations during the switch. The results suggest that the relatively slow change in the intake Manifold Air Pressure (MAP) and actuation time of the Variable Valve Timing (VVT) are the main causes of undesired AFR and RGF fluctuation, and hence unacceptable NIMEP fluctuation. We also found large cylinder-to-cylinder AFR variation in the transition. Therefore, besides throttle opening control and VVT shifting, cyclic and individual cylinder fuel injection control is necessary to achieve a smooth transition. The control method was developed and implemented in the test engine, and resulted in much reduced NIMEP fluctuations during the switch. The instantaneous AFR and RGF measurements could be adopted to develop more sophisticated control methods for SI-HCCI-SI transition.

A Stochastic Reactor Model (SRM) has been used to simulate the transition from Spark Ignition (SI) mode to Homogeneous Charge Compression Ignition (HCCI) mode in a four cylinder in-line four-stroke naturally aspirated direct injection SI engine with cam profile switching. The SRM is coupled with GT-Power, a one-dimensional engine simulation tool used for modelling engine breathing during the open valve portion of the engine cycle, enabling multi-cycle simulations. The model is initially calibrated in both modes using steady state data from SI and HCCI operation. The mode change is achieved by switching the cam profiles and phasing, resulting in a Negative Valve Overlap (NVO), opening the throttle, advancing the spark timing and reducing the fuel mass as well as utilising a pilot injection. Experimental data is presented along with the simulation results. The model is used to investigate key control parameters and their effects on parameters that are difficult to measure experimentally. The effect of the spark in the first HCCI cycles is found to have a major impact on the stability of the transition.

In this work, the formation of soot in a Direct Injection Spark Ignition (DISI) engine is simulated using the Stochastic Reactor Model (SRM) engine code. Volume change, convective heat transfer, turbulent mixing, direct injection and flame propagation are accounted for. In order to simulate flame propagation, the cylinder is divided into an unburned, entrained and burned zone, with the rate of entrainment being governed by empirical equations but combustion modelled with chemical kinetics. The model contains a detailed chemical mechanism as well as a highly detailed soot formation model, however computation times are relatively short. The soot model provides information on the morphology and chemical composition of soot aggregates along with bulk quantities, including soot mass, number density, volume fraction and surface area. The model is first calibrated by simulating experimental data from a Gasoline Direct Injection (GDI) Spark Ignition (SI) engine. The model is then used to simulate experimental data from the literature, where the numbers, sizes and derived mass particulate emissions from a 1.83L, 4-cylinder, 4 valve production DISI engine were examined. Experimental results from different injection and spark timings are compared with the model and the qualitative trends in aggregate size distribution and emissions match the exhaust gas measurements well.

A previously developed Stochastic Reactor Model (SRM) is used to simulate combustion in a four cylinder in-line four-stroke naturally aspirated direct injection Spark Ignition (SI) engine modified to run in Homogeneous Charge Compression Ignition (HCCI) mode with a Negative Valve Overlap (NVO). A portion of the fuel is injected during NVO to increase the cylinder temperature and enable HCCI combustion at a compression ratio of 12:1. The model is coupled with GT-Power, a one-dimensional engine simulation tool used for the open valve portion of the engine cycle. The SRM is used to model in-cylinder mixing, heat transfer and chemistry during the NVO and main combustion. Direct injection is simulated during NVO in order to predict heat release and internal Exhaust Gas Recycle (EGR) composition and mass. The NOx emissions and simulated pressure profiles match experimental data well, including the cyclic fluctuations. The model predicts combustion characteristics at different fuel split ratios and injection timings. The effect of fuel reforming on ignition timing is investigated along with the causes of cycle to cycle variations and unstable operation. A detailed flux analysis during NVO unearths interesting results regarding the effect of NOx on ignition timing compared with its effect during the main combustion. © 2009 SAE International.

This paper presents experimental results and a new computational model that investigate Cycle to Cycle Variations (CCVs) in a Spark Ignition (SI) engine. An established Stochastic Reactor Model (SRM) previously used to examine Homogeneous Charge Compression Ignition (HCCI) combustion has been extended by spark initiation, flame propagation and flame termination sub-models in order to simulate combustion in SI engines. The model contains a detailed chemical mechanism but relatively short computation times are achieved. The flame front is assumed to be spherical and centered at the spark location, and a pent roof and piston bowl geometry are accounted for. The model is validated by simulating the pressure profile and emissions from an iso-octane fueled single cylinder research engine that showed low CCVs. The effects of key parameters are investigated. Experimental results that show cycle to cycle fluctuations in a four-cylinder naturally aspirated gasoline fueled SI engine are presented. The model is then coupled with GT-Power, a onedimensional engine simulation tool, which is used to simulate the breathing events during a multi-cycle simulation. This allows investigation of the cyclic fluctuations in peak pressure. The four cylinder engine has been modified so that transition to HCCI operation is possible via cam profile switching. It is then demonstrated why the detailed exhaust composition obtained may be necessary to simulate the transition between SI-HCCI-SI engine operating modes in future work.