Engine performance during transient and steady-state operation with oxygenated fuels

Owing to the increasing share of biofuels in combustion engines, use of these oxygenated fuels instead of diesel should be evaluated under different engine operating conditions. This paper studies the influence of oxygenated fuels on engine performance parameters under transient, compared to steady-state, operation on a six-cylinder, turbocharged, compression-ignition engine with a common rail injection system. The fuels used in this study were diesel, waste cooking biodiesel, and triacetin (as a highly oxygenated additive). A custom test was used to investigate different engine performance parameters during acceleration, load increase, and steady-state modes of operation. Additionally, a legislative transient cycle (NRTC), composed of many discrete transient modes, was used to study engine performance during a whole transient cycle. In this paper, different engine performance-related parameters were investigated, such as IMEP, BMEP, FMEP, turbocharger lag, air-to-fuel ratio, engine speed and torque, start of injection, start of combustion, injection pressure, maximum in-cylinder pressure, maximum rate of pressure rise, intake and exhaust manifold pressures, and CoV of IMEP. The investigation demonstrates that engine behavior during transient operation is different from steady-state operation. Results during NRTC indicated that, in comparison with diesel, the oxygenated fuels have lower IMEP (up to 18.7%), BMEP (up to 21.7%), and FMEP (up to 12.7%). During transient modes of the custom test, using oxygenated fuels rather than diesel resulted in higher indicated torque, maximum in-cylinder pressure, and maximum rate of pressure rise; however, during steady-state, most of the oxygenated fuels had lower values in these three parameters. Each advance in SOI corresponds to a rise in the maximum in-cylinder pressure and in the maximum rate of pressure rise. Oxygenated fuels had lower intake manifold pressure and CoV of IMEP than diesel. Different fuel properties were used to interpret engine behavior.