Predicting HCCI Auto-Ignition Timing by Extending a Modified Knock-Integral Method

One major challenge in Homogeneous Charge Compression Ignition (HCCI) combustion is the difficulty in controlling the timing of auto-ignition which is dependant on mixture conditions. Understanding the effect of modifying the properties of the engine charge on the start of combustion is essential to be able to predict and control the auto-ignition timing. The purpose of this work is to develop a realtime model for predicting HCCI auto-ignition timing.

The standard Livengood and Wu Knock-Integral Method (KIM) is modified to work with values that are easier to measure compared with the instantaneous in-cylinder parameters required in the original KIM. This modified Knock-Integral Method (MKIM) is developed and is then parameterized using HCCI Thermokinetic Kinetic Model (TKM) simulations for a single cylinder engine. Estimating the MKIM parameters is done using an off-line optimization technique. Once the parameters have been identified, the MKIM needs only the rate of Exhaust Gas Recirculated (EGR), equivalence ratio, intake manifold temperature and intake manifold pressure to predict auto-ignition timing. The MKIM is validated with the experimental data from the single cylinder engine in HCCI operation by varying equivalence ratio, EGR level, engine speed, and intake temperature for three different blends of Primary Reference Fuels (PRF) at octane values of 0, 10 and 20.