Effects of iso-butanol/diesel and n-pentanol/diesel blends on performance and emissions of a DI diesel engine under premixed LTC (low temperature combustion) mode

This study attempts to achieve simultaneous reduction of smoke and NOx emissions using a combination of low EGR, retarded injection timing and diesel fuel reformulation (with low cetane number alcohols) to enable a partially premixed low temperature combustion (LTC) mode in DI diesel engine. Two higher alcohol/diesel blends, B40 (40% iso-butanol-60% diesel) and P40 (40% n-pentanol-60% diesel) blends were prepared and tested under the combination of three EGR rates (10%, 20% and 30%) and two injection timings (23 degrees and 21 degrees CA bTDC) at high loads and constant engine speed. The performance and emission characteristics of the engine under these conditions are investigated. Results indicate that B40 gives a longer ignition delay, higher peak pressure and higher premixed heat release rate than P40. B40 has superior EGR tolerance and better influence on NOx-smoke trade-off when compared to P40. At retarded injection timing (21 degrees CA bTDC) and 30% EGR, B40 presented simultaneous reduction of NOx (down arrow 41.7%) and smoke (down arrow 90.8%) emissions with diesel-like performance while P40 presented simultaneous reduction of NOx (down arrow 39.3%) and smoke (down arrow 15%) emissions with a small drop in performance. It was found that B40 presented better smoke suppression characteristics than P40. Smoke emissions of both blends increased drastically beyond 30% EGR. HC emissions increased and CO emissions remained low for both blends at all EGR rates. The combination of low EGR, late injection and higher alcohol/diesel blends can achieve partially premixed LTC and reduce smoke and NOx emissions simultaneously. (C) 2015 Elsevier Ltd. All rights reserved.