An investigation into the RCCI engine operation under low load and its achievable operational range at different engine speeds
•The response of allowable RCCI operating range to engine speed variation is studied.•The RCCI and diesel LTC engine operations at are compared at low engine load.•The potential of expanding RCCI operating range at low engine speed is explored. Reactivity controlled compression ignition (RCCI) is de...
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Published in | Energy conversion and management Vol. 124; pp. 399 - 413 |
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Main Authors | , , , , , |
Format | Journal Article |
Language | English |
Published |
Elsevier Ltd
15.09.2016
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Subjects | |
Online Access | Get full text |
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Summary: | •The response of allowable RCCI operating range to engine speed variation is studied.•The RCCI and diesel LTC engine operations at are compared at low engine load.•The potential of expanding RCCI operating range at low engine speed is explored.
Reactivity controlled compression ignition (RCCI) is demonstrated as a promising combustion strategy to achieve high efficiency and clean combustion. However, less effort has been devoted to examine the achievable RCCI operational range over a wide range of engine speed. In addition, previous studies have found that superior EGR rate and high diesel/gasoline fuel ratio are required to ease the extension of the low-load operating range of RCCI regime. Even then, relatively high CO and HC (unburned hydrocarbon) emissions and the accompanying fuel con-sum ption penalty still remain a problem to be resolved. Therefore, in this work the potential of diesel-fueled LTC to achieve simultaneously low NOx and soot emissions while maintaining high thermal efficiency at low load (IMEP ≈0.23–0.26MPa) is investigated and compared with the gasoline/diesel RCCI strategy. The results show that the diesel LTC operation can yield slightly higher soot and NOx emissions (soot: 0.002g/kWh, NOx: 0.446g/kWh), but CO and HC emissions as well as the fuel consumption are much lower than the RCCI strategy, implying the diesel LTC regime may be more suitable for low-load operations. In addition, the RCCI operational range at speeds ranging from 900 to 2500r/min is determined, the results show that the maximum achievable load (IMEP) increases with an increase in speed, and a maximum IMEP of 1.2MPa can be achieved at an engine speed of 2300r/min. Ultra-low NOx and soot emissions (soot<0.003g/kWh, NOx<0.4g/kWh) can be achieved under the maximum loading conditions at each speed investigated. However, high levels of CO and HC emissions still remain a big problem to be solved. The lowest fuel consumption (168.6g/kWh) occurred at an engine speed of 1900r/min with an EGR rate of 56%, and the corresponding indicated thermal efficiency is up to 50%. In addition, intake boosting can be very effective for expanding the RCCI operating range at low engine speed (900r/min), but excessive pressure rise rates could become problematic with increased amount of fuel injection. |
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ISSN: | 0196-8904 1879-2227 |
DOI: | 10.1016/j.enconman.2016.07.026 |