Application of biobutanol in advanced CI engines – A review

Abstract

Butanol is of particular interest as a renewable biofuel for advanced CI engines due to several superior fuel properties over methanol and ethanol. This review is, therefore, concentrated on the application of biobutanol in advanced compression engines including LTC, HCCI, etc. The physico-chemical properties of biobutanol and fundamental studies of biobutanol in advanced CI engine condition are discussed. As one of important fundamental combustion characteristics, ignition delay time can be measured by four different methods based on the experimental apparatus such as shock tube, rapid compression machine (RCM), HCCI engine and ignition quality tester.In LTC mode, in-cylinder injection of n-butanol-diesel blends required appropriate control over the injection timing, injection pressure and EGR. In case of mixture formation by dual fuel injection, n-butanol/PFI+diesel/DI was broadly studied. In the viewpoint of longest ignition delay and lowest soot emissions, higher thermal efficiency with certain EGR of iso-butanol/diesel blends among four isomers-diesel blends, more studies on the combustion and emission characteristics of iso-butanol/diesel blends in LTC are strongly required.Studies concerning HCCI combustion mode can be classified into three groups based on PFI, in-cylinder injection and dual fuel injection. In the mixture formation by in-cylinder injection, neat n-butanol HCCI combustion was mainly investigated. In the dual fuel injection strategy, butanol/PFI and diesel/DI HCCI combustion was chiefly studied. There is no study on the use of butanol/biodiesel blends with in-cylinder injection in HCCI combustion mode. Major findings of this review suggested that similar to those in other HCCI studies, the butanol HCCI combustion encounters problems of the lack of desired controllability over the ignition timing and combustion phasing.According to the literature review in this study, the use of n-butanol as neat or blends with diesel has shown promising potential for enabling LTC and HCCI operation on diesel engines. Among various fuel properties, the long ignition delay, high oxygen content, and high volatility of n-butanol are major contributors to improve the fuel-air mixing and lower the NOx and soot emission.