Impact of acetaldehyde and NO addition on the 1-octene oxidation under simulated HCCI conditions

Abstract

Due to more and more stringent restrictions on vehicle exhaust emissions, low temperature combustion in automotive engines becomes more and more important. Low temperature combustion is achieved by high rates of Exhaust Gas Recirculation (EGR). EGR gases are used to dilute the fuel/air mixture in the engine and to control ignition delay times. However, nowadays, EGR is also supposed to have chemical impact on the Homogeneous Charge Compression Ignition (HCCI) engine combustion. First, the effects of NO and acetaldehyde addition were studied performing HCCI engine experiments with different concentrations of NO and CH 3CHO. Since the impact of EGR compounds on engine control is difficult to understand in an engine itself, experiments were performed in a Jet-Stirred Reactor (JSR) where conditions are well-controlled. The effects of the addition of NO (100 ppm) and acetaldehyde (200 ppm) on 1-octene oxidation were studied at 1.013 MPa, under dilute conditions. According to the literature, a complex impact of NO was observed, but in contrast to the assumption that aldehydes could have a strong impact on oxidation kinetics, only moderate effects of acetaldehyde were found but leading to a significant impact on combustion in an HCCI engine. However, a synergy between NO and acetaldehyde on the oxidation of 1-octene was observed when these species were added simultaneously leading to an inhibition of fuel oxidation at low temperatures, an important reduction of the NTC-effect, and a promotion of fuel oxidation in higher temperatures. These results tend to demonstrate the importance of taking into account the complexity of EGR composition.