Control-oriented model-based ignition timing prediction for high-degrees-of-freedom spark ignition engines

Abstract

The pressure to improve automotive fuel economy and emissions has driven the introduction of more complex spark ignition engines. As the number of control actuators increases, traditional ignition timing calibration and control methods become restrictive, creating a need for new feedforward approaches to manage transient operation. This research was conducted to determine whether a control-oriented turbulent flame entrainment model could be developed to predict the ignition timing of an engine with a large number of control actuators. A physics-based approach is used to capture the influence of additional control actuators on the complex interactions affecting the ignition timing. Each actuator is characterized by its influence on the fundamental combustion parameters, such as the residual gas fraction and the turbulence intensity. Experimental results are used to generate semiempirical input and combustion models that are capable of running in real time within an engine controller. The model is used to predict the combustion duration, from the spark to 50% mass fraction burned, at every crank angle position within a reasonable ignition timing window for each engine operating point. With minimal engine mapping, the model was capable of predicting the spark timing to within several degrees of ideal values, demonstrating the feasibility of this approach for use in high-degrees-of-freedom spark ignition engines.

Premixed Combustion in Spark Ignition Engines and the Influence of Operating Variables

“…The polytropic index of compression n does vary with engine conditions, but a constant value of 1.29 has been used to yield acceptable overall results [47]; some researchers [5] have suggested a linear fit to measured or estimated values of charge dilution mass fraction. The charge density at spark timing is calculated from pressure and temperature advancing the hypothesis of ideal gas mixture, or simply by the ratio of total trapped mass m tot and available chamber volume V ST .…”

“…Nevertheless, these models also require some form of calibration using real measurements. Recent published work by Hall et al [47] and by Prucka et al [5] offers examples of relatively simple phenomenological flame propagation and entrainment models, suited for inclusion into fastexecution ST control algorithms, to ensure optimal phasing of the 50% MFB location (i.e. 7 or 8 CA degree ATDC) and improve engine efficiency and fuel economy.…”

“…The recent work by Hall et al [47] outlines a relatively simple, physics-based, quasi-dimensional flame propagation model capable of capturing the influence of variable valve timing, ethanol/gasoline blend ratio and other parameters relevant to modern SI engines, to provide estimates of the 50% MFB location and hence phase the combustion period most appropriately with respect to TDC. The model advanced by Prucka et al [5] is similarly used for predicting best ignition timing in complex SI engine architectures (featuring not only VVT technology but also a charge motion control valve), but it is different in its logic as it relies on a simplified adaptation of the turbulent flame entrainment concept originally introduced by Blizard and Keck [61]. The present section introduces the reader to the first type of combustion models, which is less reliant on complex descriptions of fuel burning rate and turbulence regimes, and hence more readily implementable.…”

“…These have included the electronic fuel injection system, exhaust emissions after-treatment, Exhaust Gas Recirculation and, increasingly, the use of some form of variable actuation valve train system. The modern SI engine, addressed to as high-degree-of-freedom engine by Prucka et al [5], may also feature flexible fuel technology, typically to allow running on ethanol-gasoline blended fuels.…”

A New Approach for Ignition Timing Correction in Spark Ignition Engines Based on Cylinder Tendency to Surface Ignition

“…Knock restricts the combustion efficiency and engine performance in spark ignition (SI) engines. With the direct relation between the spark advance and knock; knock is a limitation that affect the ignition timing [1]. Engine designer try to optimize the parameters that contribute in knock phenomena.…”