Search Results

The simultaneous reduction of engine-out nitrogen oxide (NOx) and particulate emissions via low-temperature combustion (LTC) strategies for compression-ignition engines is generally achieved via the use of high levels of exhaust gas recirculation (EGR). High EGR rates not only result in a drastic reduction of combustion temperatures to mitigate thermal NOx formation but also increases the level of pre-mixing thereby limiting particulate (soot) formation. However, highly pre-mixed combustion strategies such as LTC are usually limited at higher loads by excessively high heat release rates leading to unacceptable levels of combustion noise and particulate emissions. Further increasing the level of charge dilution (via EGR) can help to reduce combustion noise but maximum EGR rates are ultimately restricted by turbocharger and EGR path technologies.

Single cylinder optical engines are used for internal combustion (IC) engine research as they allow for the application of qualitative and quantitative non-intrusive, diagnostic techniques to study in-cylinder flow, mixing, combustion and emissions phenomena. Such experimental data is not only important for the validation of computational models but can also provide a detailed insight into the physical processes occurring in-cylinder which is useful for the further development of new combustion strategies such as gasoline homogeneous charge compression ignition (HCCI) and Diesel low temperature combustion (LTC). In this context, it is therefore important to ensure that the performance of optical engines is comparable to standard all-metal engines. A comparison of optical and all-metal engine combustion and emissions performance was performed within the present study.

Planar laser-induced fluorescence (LIF) imaging of formaldehyde (CH2O) and OH has been performed to investigate the homogeneous charge, compression ignition (HCCI) combustion process inside the piston bowl of an optically-accessible, direct injection Diesel-fueled HCCI engine. In particular, the effects of charge dilution and the adoption of single and split injection strategies on the two-stage HCCI combustion have been studied. Results obtained show that the level of exhaust gas recirculation (EGR) significantly affects the pre-combustion or so called cool flame phase during which formaldehyde is detected. The cool flame phasing as indicated by the formation of this intermediate species is unaffected by the EGR level however, auto-ignition timing which marks the start of main combustion is inevitably advanced following a reduction in EGR and this ultimately determines the formaldehyde lifetime and consequently the degree of homogeneity attained.