CI/ PCCI Combustion Mode Switching of Diesohol Fuelled Production Engine

Paper #:
  • 2017-01-0738

Published:
  • 2017-03-28
Abstract:
Premixed charge compression ignition (PCCI) combustion has the potential to utilise alternative fuels such as alcohols. PCCI combustion emits significantly lower oxides of nitrogen (NOx) and particulate matter (PM) and resulted thermal efficiency similar to conventional CI engines. However, PCCI combustion cannot be used in production grade engines due to its incapability to operate at high engine loads. This study focussed on development of hybrid combustion engine, which can operate in both combustion modes such as CI combustion as well as PCCI combustion mode. Hybrid combustion system was controlled by an open ECU, which varied the fuel injection parameters for mode switching between CI and PCCI combustion modes. At low-to-medium engine loads, engine was operated in PCCI combustion mode and at higher engine loads ECU automatically switched the engine operation in CI combustion mode. Experiments were carried out using diesohol (10% ethanol in mineral diesel, v/v) at constant engine speed (1500 rpm) and load was varied from idling to full load (6 bar BMEP). To explore the emission behaviour in different combustion modes and mode transition periods, continuous sampling of exhaust gas was carried out, which included regulated emission measurement, unregulated gaseous species measurement and particulate measurement. Results showed significantly lower NOx and particulate from PCCI combustion however performance of PCCI combustion was slightly inferior compared to CI combustion. During mode transition from PCCI to CI combustion mode, sudden increase in exhaust gas temperature (~ 75°C) was the main reason for improved CI combustion. Slightly higher concentration of unregulated emission species such as SO2, HCHO, etc. in PCCI combustion was an important observation of this study. Relatively lower concentration of cyclic compounds in PCCI combustion compared to CI combustion is another advantage of PCCI combustion, which reduces the toxicity of exhaust gas. Particulate number-size distribution showed the presence of nano-particles in CI combustion however in PCCI combustion, most of the particulates lied in accumulation size range.
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