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

• Iso-butanol and n-pentanol were used to enable a partially premixed LTC in a diesel engine.
• Combustion-phasing and charge-dilution were controlled by EGR and injection timing.
• Test fuels presented enhanced premixed combustion with high peak pressures and HRR.
• Simultaneous reduction of NOx/PM was realized with test fuels under moderate EGR & late injection.
• Iso-butanol blends offered better EGR tolerance than n-pentanol blends.

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° and 21° 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° CA bTDC) and 30% EGR, B40 presented simultaneous reduction of NOx (↓ 41.7%) and smoke (↓ 90.8%) emissions with diesel-like performance while P40 presented simultaneous reduction of NOx (↓ 39.3%) and smoke (↓ 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.