A sparkplug ion sensor can be used to measure the ion current in a homogeneous charge compression ignition (HCCI) engine, providing insight into the ion chemistry inside the cylinders during combustion. HCCI engines typically operate at lean equivalence ratios (•) at which the ion current becomes increasingly indistinguishable from background noise. This paper investigates the effect of fuel additives on the ion signal at low equivalence ratios, determines side effects of metal acetate addition, and validates numerical model for ionization chemistry. Cesium acetate (CsOAc) and potassium acetate (KOAc) were used as additives to ethanol as the primary fuel. Concentration levels of 100, 200, and 400mg/L of metal acetate-in-ethanol are investigated at equivalence ratios of 0.08, 0.20, and 0.30. The engine experiments were conducted at a boosted intake pressure of 1.8bar absolute and compared to naturally aspirated results. Combustion timing was maintained at 2.5° after top-dead-center (ATDC), as defined by the crank angle degree (CAD) where 50% of the cumulative heat release occurs (CA50). CsOAc consistently produced the strongest ion signals at all conditions when compared to KOAc. The ion signal was found to decrease with increased intake pressure; an increase in the additive concentration increased the ion signal for all cases. However, the addition of the metal acetates decreased the gross indicated mean effective pressure (IMEPg), maximum rate of heat release (ROHR), and peak cylinder pressure. Experimental results were used to validate ion chemistry mechanisms for cesium and potassium using a single-zone numerical engine model.
Bibliographical noteFunding Information:
This study was supported by LLNL under award number B586434 (Low Temperature Combustion Chemistry at Boost Pressures for Surrogate Fuels and Ethanol Use in HCCI Engine Experiments). The KOAc additive for this study was provided by T.S. Lee at the Joint BioEnergy Institute (JBEI) led by Lawrence Berkeley National Laboratory (LBNL). Additional thanks to Jacob Cross, Franciel Gusberti, Samveg Saxena, Darko Kozarac, David Vuilleumier, Daniel Schuler, Tung Phan, and Aditya Desai for their contributions.
© 2015 Published by Elsevier Ltd.
- Fuel additive
- Homogeneous charge compression ignition
- Internal combustion
- Ion sensing
ASJC Scopus subject areas
- Renewable Energy, Sustainability and the Environment
- Nuclear Energy and Engineering
- Fuel Technology
- Energy Engineering and Power Technology