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Ion sensors have been shown to be a low-cost and robust method of measuring start of combustion (SOC) in Homogeneous Charge Compression Ignition (HCCI) engines. The combustion event in an HCCI engine is governed by temperature sensitive chemical-kinetics and is highly fuel dependent. Autoignition variability between various fuels can also affect emissions, efficiency, and overall operating range of the HCCI engine. Ion sensors (i.e. modified spark-plugs) can be used pragmatically to detect the combustion event for various fuels in HCCI engines over a wide range of operating conditions. An investigation of the ion currents produced from the combustion of gasoline, ethanol, and n-heptane in a 1.9L 4-cylinder VW TDI diesel engine (converted to run in HCCI mode) is conducted over a range of equivalence ratios, intake temperatures, and intake pressures. Gasoline, ethanol and n-heptane have diverse autoignition characteristics which affect the overall operation of the HCCI engine.

We numerically simulate a Homogeneous Charge Compression Ignition (HCCI) engine fuelled with a blend of ethanol and diethyl ether by means of a stochastic reactor model (SRM). A 1D CFD code is employed to calculate gas flow through the engine, whilst the SRM accounts for combustion and convective heat transfer. The results of our simulations are compared to experimental measurements obtained using a Caterpillar CAT3401 single-cylinder Diesel engine modified for HCCI operation. We consider emissions of CO, CO2 and unburnt hydrocarbons as functions of the crank angle at 50% heat release. In addition, we establish the dependence of ignition timing, combustion duration, and emissions on the mixture ratio of the two fuel components. Good qualitative agreement is found between our computations and the available experimental data.

The influence of the small amounts (1-3%) of the additive di-tertiary butyl peroxide (DTBP) on the combustion event of Homogeneous Charge Compression Ignition (HCCI) engines was investigated using engine experiments, numerical modeling, and carbon-14 isotope tracing. DTBP was added to neat ethanol and diethyl ether (DEE) in ethanol fuel blends for a range of combustion timings and engine loads. The addition of DTBP to the fuel advanced combustion timing in each instance, with the DEE-in-ethanol mixture advancing more than the ethanol alone. A numerical model reproduced the experimental results. Carbon-14 isotope tracing showed that more ethanol burns to completion in DEE-in-ethanol blends with a DTBP additive when compared to results for DEE-in-ethanol without the additive. However, the addition of DTBP did not elongate the heat release in either case.