Advanced Diesel Combustion of a High Cetane Number Fuel with Low Hydrocarbon and Carbon Monoxide Emissions

• Published in: Energy & fuels Vol. 25; no. 4; pp. 1444 - 1456
• Main Authors: Lilik, Gregory K, Boehman, André L
• Format: Journal Article
• Language: English
• Published: American Chemical Society 21.04.2011
• Subjects: Combustion
• ISSN: 0887-0624; 1520-5029
• DOI: 10.1021/ef101653h

Advanced diesel combustion is of great interest due to its promise of simultaneously reducing emissions of nitrogen oxides (NO x ) and particulate matter (PM), while maintaining or improving efficiency. However, the extended ignition delay along with the combustion of a partially premixed charge results in excessive emissions from incomplete combustion, specifically total hydrocarbons (THC) and carbon monoxide (CO). In this study, a light-duty turbodiesel engine was operated in an advanced diesel combustion mode, specifically high efficiency clean combustion (HECC), using three different fuels including a conventional ultralow sulfur diesel fuel (diesel), a synthetic fuel produced in a high temperature Fischer−Tropsch (HTFT) process, and a synthetic fuel produced in a low temperature Fischer−Tropsch (LTFT) process. Start of injection (SOI) timing was swept from −8° ATDC to 0° ATDC to find the optimized injection timing for each fuel. The HTFT fuel, which had a derived cetane number (DCN) of 51, was found to decrease THC and CO emission by 32% and 31%, respectively, compared to the diesel fuel which had a DCN of 45. The higher ignition quality of the HTFT fuel was found to reduce emission from incomplete combustion by presumably consuming more of the fuel charge before it reached a region of the cylinder where it was too lean to effectively burn. However, with the HTFT fuel, NO x and PM emissions increased relative to the diesel baseline due to a higher peak heat release rate, presumably caused by 2% less EGR during the HTFT fuel’s operation. In contrast, the LTFT fuel with a DCN of 81 enabled an 80% reduction in THC emissions and a 74% reduction in CO emissions compared to the diesel fuel. The LTFT fuel, though having a very short ignition delay, did not increase NO x and PM emissions apparently due to the fuel burning in a shorter, less intense premixed combustion phase followed by a prominent mixing controlled combustion phase. This study revealed that a high ignition quality (DCN 81) fuel is well suited for operation under a high EGR advanced diesel mode and led to reductions in all primary pollutant emissions.