Original Article International J of Engine Research 2014, Vol 15(1) 112–122 Ó IMechE 2013 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/1468087413481345 jer.sagepub.com Cylinder-to-cylinder variation sources in diesel low temperature combustion and the influence they have on emissions Joshua Bittle, Junnian Zheng, Xingyu Xue, Hoseok Song and Timothy Jacobs Abstract Cylinder-to-cylinder variation in a multi-cylinder diesel engine was found to increase substantially when transitioning to a low-temperature combustion mode. This study was started to investigate the potential influence this effect could have on the emissions levels. Initial testing showed an imbalance in the fuel distribution that prompted this article to focus on data from before and after swapping two injectors under both conventional and low-temperature combustion modes. A significant improvement is observed in cylinder variation based both on visual heat release inspection and on mean effec- tive pressure variation. This is likely a result of a changing combination of exhaust gas recirculation and fuel distribution such that less cylinder-to-cylinder variation is present (e.g. high dilution and low fuel, switched to low dilution and low fuel). Interestingly, despite the reduced cylinder-to-cylinder variation, the results show that the emissions levels are actually not affected. Despite the lack of influence on emissions results, the cylinder-to-cylinder variation in low-temperature combustion modes is still a critical factor that could impact its ability to be implemented in a commercial setting. Further cylinder balancing was attempted and achieved by introducing small (microsecond) adjustments to each cylinder start of injection and injection duration. The balancing is effective, but due to exhaust gas recirculation imbalance, a single adjust- ment setting does not apply to both conventional and low-temperature combustion modes. Additionally, day-to-day ambient conditions also negate the effectiveness. This supports the idea that some type of consumer-based real-time automatic balancing system may be needed in the future. Keywords Cylinder balance, cylinder variation, low-temperature combustion, diesel combustion, combustion control Date received: 13 November 2012; accepted: 11 February 2013 Introduction The benefits of low-temperature combustion (LTC) are well documented and include the ability to reduce soot (particulate matter (PM)) and nitric oxide (NO) forma- tion simultaneously. 1 The drawbacks, however, have been equally well demonstrated. These drawbacks include limited load operating conditions 2 and increased products of incomplete combustion in the exhaust (carbon monoxide (CO) and hydrocarbons (HCs)). 3 Recent investigation in our group has shown significant cylinder-to-cylinder variation while operat- ing in an LTC mode. The observations are made using a medium-duty diesel engine equipped with electroni- cally controlled common rail fuel system supplying solenoid injectors. It is hypothesized that a significant portion of the perceived decrease in combustion effi- ciency (or increase in CO and HC emissions) may be a result of one or two cylinders undergoing significantly different combustion processes than the others. This could be due to differences in cylinder geometry, injec- tor behavior, air and/or exhaust gas recirculation Department of Mechanical Engineering, Texas A&M University, College Station, TX, USA Corresponding author: Timothy Jacobs, Department of Mechanical Engineering, Texas A&M University, 3123 TAMU, College Station, TX 77843-3123, USA. Email: tjjacobs@tamu.edu