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The use of a spark plug ion sensor to detect combustion timing in a homogeneous charge compression ignition (HCCI) engine is a technique that could alleviate the need for pressure transducers, a more expensive alternative. One disadvantage of this approach is the difficulty in obtaining a strong signal at lower equivalence ratios. This article addresses and compares three ion sensing circuitries, namely a voltage follower, a notch filter circuit that removes the 60-Hz wall noise, and a notch filter whose output is coupled to a custom-built “integrator” circuit. The circuit optimizations are aimed at improving signal strength and reliability. The ion signal present in the combustion chamber is experimentally investigated in a 1.9-L Volkswagen engine, modified for HCCI operation and fueled with gasoline. Experiments are conducted across different intake temperatures, pressures, and equivalence ratios. It was found that the custom-built circuit provided the best ion signal strength and reliability. [ABSTRACT FROM PUBLISHER]

Longer chain alcohols, such as butanol, possess major physiochemical advantages over ethanol as bio-components for gasoline, including higher energy content, better engine compatibility, and less water solubility. In this study, two butanol isomers (n-butanol and isobutanol) are investigated as potential fuels for Homogeneous Charge Compression Ignition (HCCI) engines. Wide ranges of intake pressure and equivalence ratio are investigated and the results are presented in comparison to ethanol and gasoline as reference fuels. Under all tested conditions, the butanol isomers require lower intake temperatures for a fixed combustion phasing, indicating higher HCCI reactivity. Both isomers show single-stage ignition behavior at all test points and behave similarly in regard to the combustion stability. Engine operation using n-butanol is slightly more stable under all conditions and misfiring occurs slightly later under very lean and naturally aspirated conditions. Similar to gasoline, n-butanol shows a higher heat release rate (HRR) at the beginning of combustion. The intermediate temperature heat release (ITHR) lowers the coefficient of variation (CoV) of IMEPg (gross indicated mean effective pressure), especially at retarded combustion timing and lean mixtures. However, the knock resistance of n-butanol is lower compared to isobutanol and the other tested fuels. The exhaust emissions of the two butanol isomers are in the same range as the two reference fuels. Overall, the results indicate that butanol is suited for use as a fuel in HCCI engines, either in neat form or in blend with gasoline. [ABSTRACT FROM AUTHOR]

As an approach to replace pressure transducers, ion current sensing is a promising candidate for overcoming the difficult task of controlling the start of combustion in Homogeneous Charge Compression Ignition (HCCI) engines which require feedback from previous cycles. In this study, cyclic variations and prior-cycle effects of ion current signals are analyzed by comparing against pressure transducer signals using time-series methods in an HCCI engine. Additionally, the effects of various calibrated ion signal intensities are tested by adding cesium acetate (CsOAc) to the base fuel. Nonlinear characteristics of ion current signals are identified to cause strong cyclic variations through a single-zone model analysis with different equivalence ratios. By analyzing the time series, return maps, and coefficient of variations (CoV), the study finds that the stability of the ion signals can be largely improved by adding CsOAc due to the low ionization energy. After reconstructing a complex, nonlinear dynamical system model with symbol-sequence statistics, the measured cycle-resolved data of the ion current signal is analyzed to determine the pattern structures within prior cycles of fixed length, which is optimized by a modified Shannon entropy calculation. The results suggest that long, consecutive symbols of the ion current signal can be reliably predicted through the application of designed deterministic patterns especially when a small amount of CsOAc is added, although the ion current signal is normally considered a localized information provider and affected by many dynamical factors. Consequently, ion current signals are very promising for model-based control systems in HCCI engines with tolerable amounts of signal enhancing additives. [ABSTRACT FROM AUTHOR]