Effect of common rail pressure on the relationship between BSFC and BSPM at NOx parity.

Open Access
- Author:
- Prabhakar, Bhaskar
- Graduate Program:
- Mechanical Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- July 02, 2009
- Committee Members:
- Andre Louis Boehman, Thesis Advisor/Co-Advisor
Andre Louis Boehman, Thesis Advisor/Co-Advisor - Keywords:
- injection timing
NOx
BSPM
BSFC
rail pressure - Abstract:
- This study concerns the effect of common rail pressure on the relationship between brake specific fuel consumption (BSFC) and brake specific particulate matter (BSPM) at NOx parity using a DDC/VM-Motori 2.5 L, 4 cylinder, turbocharged, direct injection, light duty diesel engine. The research was divided into two tests. Test 1 was performed holding the load constant (40% load at the rated speed) while speed was increased in steps of 300 rpm from 1500 rpm to 2100 rpm. Test 2 was performed holding the speed constant (1800 rpm) while the load was varied in steps of 7.5% from 40% to 55%. Three rail pressures of 425 bar, 500 bar and 575 bar were selected to be within a safe operating range for the engine. Injection was limited to single pulse injection for ease of control. Ultra low sulfur diesel (ULSD) was used as the fuel to perform the experiments. An engine map of the exhaust gas composition, mainly NOx, was created at the given speeds, loads and rail pressures. A sweep of the injection timing was performed over a given range of operating conditions and points of constant NOx were identified on a brake specific basis. While conducting these tests, the influence of engine parameters on performance and emissions were determined. These included the effects of speed and load on specific fuel consumption and NOx, and the effect of injection timing on BSFC. Results confirmed the well established trend that retarding the injection timing helped reduce NOx but at the expense of fuel consumption. Increasing the rail pressure increased NOx emissions while particulate matter (PM) was reduced. Findings at constant NOx indicated the dominance of either speed or injection timing which resulted in high PM at a few conditions of rail pressure and speed. Heat release profiles and bulk temperatures from Test 2 indicated several trends concerning PM formation and its oxidation. A reduction in the engine load resulted in less PM exhausted from the engine. A high bulk temperature from high engine load conditions indicated a preference of PM oxidation to its formation. To determine the influence of engine parameters on soot reactivity, particulate matter was collected at six different conditions at constant NOx for further investigation using thermogravimetric analysis (TGA). Raman spectroscopy was performed on all of these samples to determine the degree of disorder in the primary soot particles to support observations from TGA. Results suggested that increasing the rail pressure made soot more reactive, while a significant impact of speed and injection timing on reactivity was observed, whose trends could not be justified on the basis of a single parameter.