Test set-up and experimentation

Test set-up and experimentation

The feasibility of using the Taguchi method to optimize selected engine design/operating parameters for low emission was investigated using a Dhandapani Foundary (DPF) diesel engine in Part-I1. In order to examine whether the variation in key combustion parameters have the same effect and influence on every diesel engine of any make, the same research methodology was adopted on TEXVEL diesel engine with the same hardware configurations. Extensive research into the mechanisms governing diesel combustion and emissions has already been reported2,3. The vast amount of investigation done in the diesel combustion and emissions still not well understood due to the complex interrelationships that exist between combustion system parameters and fuel injection system parameters. Taguchi developed multivariate experimental techniques4,5 using orthogonal design arrays that allow one to isolate the effect of a single parameter on a particular response characteristic. Taguchi methods have been most extensively used in industrial and manufacturing sectors; their application to investigate diesel combustion and emissions has been very limited6. The objective of this research study was to examine the effects of changes in several key combustion and fuel injection system parameters on engine exhaust using Taguchi methods to have a better understanding of how these changes affect the diesel combustion and emission formation processes.

Experimental Procedure

Test set-up and experimentation

 A test rig has been installed for experimentation to measure the NOX, CO, HC and smoke levels of engine emissions. The rig comprises of fuel tank, manometer, air tank, electronic temperature measuring unit, fuel injection system, and exhaust gas analyzer. A single cylinder, direct injection TEXVEL engine having bore (114 mm) and stroke (140 mm) was taken for investigation. Fig. 1 shows the experimental test set-up put in the research laboratory at Government College of Technology, Coimbatore.

 Steady state tests were conducted on diesel engine with 18 different hardware configurations at 40% and 60% of maximum load during the experiment. The injector unit was removed often to change the nozzle/nozzle protrusion. The trials associated with the change of piston-to-head clearance (gasket change)  were  tested  in  random order to save testing

A statistical analysis was done for the experimental data obtained which are shown in Table A2 from the L18 experiment. The average emission responses and S/N ratios were calculated for each control factor. Analysis of variance (ANOVA) was performed to identify the most significant control parameters and to quantify their effects on NOX, CO, HC and smoke. Table 3 shows variance (Fo) and percentage of contribution ratio (r).

Response curve analysis

 Response curve analysis is aimed at determining influential parameters and their optimum levels. Figs 2 and 3 show significant effects for each emission response at each factor level for 40% Wmax and 60% Wmax  respectively. The S/N ratios for the different emission responses were calculated at each factor level and the average effects were determined by taking the total of each factor level and dividing by the number of data points in that total. The greater difference between the levels, the parametric influence will be much. The parameter level having the highest S/N ratio corresponds to the parameters setting indicates lowest emission.

 Referring (Fig. 2) the response curve at 40% Wmax for the CO emissions, the highest S/N ratio was observed at nozzle spray holes (4 holes), piston-to-head clearance (1.8 mm), nozzle protrusion (4.35 mm), start of injection timing (25.3 bTDC), injection control pressure (170 mm) and swirl level (full throttle open). Similarly the optimum parameter setting for lowest HC emissions were found to be a nozzle spray holes (4 holes), piston-to-head clearance (1.8 mm), nozzle protrusion (4.35 mm), start of injection timing (25.3 before TDC), injection control pressure (170 atm) and swirl level (full throttle open). Smoke emissions were lowest at nozzle spray holes (4 holes), piston-to-head clearance (1.4 mm), nozzle protrusion (4.35 mm), start of injection timing (25.3 before TDC), injection control pressure (160 atm) and swirl level (full throttle open). NOX emissions were lower at nozzle spray holes (3 holes), piston-to-head clearance (1.2 mm), nozzle protrusion (3.4 mm), start of injection timing (25.3 before TDC), injection control pressure (180 atm) and swirl level (full throttle).

Referring (Fig. 3) the response curve, looking 60% Wmax  for the CO emissions, the highest S/N ratio was observed at nozzle spray holes (4 holes), piston-to-head clearance (1.8 mm), nozzle protrusion (4.35 mm), start of injection timing (25.3 before TDC), injection control pressure (170 atm) and swirl level (full throttle open). Average HC emission was lowest for nozzle spray holes (4 holes), piston-to-head clearance (1.8 mm), nozzle protrusion (4.35 mm), start of injection timing (25.3 bTDC), injection control pressure (170 mm) and swirl level (full throttle open). Smoke emission were lowest at nozzle spray holes (4 holes), piston-to-head clearance (1.8 mm), nozzle protrusion (2.5 mm), start of injection timing (25.3 before TDC), injection control pressure (160 atm) and swirl level (full throttle open). NOX emissions were lowest at nozzle spray holes (3 holes), piston-to-head clearance (1.2 mm), nozzle protrusion (3.4 mm), start of injection timing (25.3 before TDC), injection control pressure (170 atm) and swirl level (full throttle open).

Finding optimum parameter settings

 Table 4 summarize the optimum parameter setting determined for each response at 40% Wmax and 60% Wmax. Note that the term optimum reflects only the optimal combination of the parameters defined by this experiment. Summary table needs to be constructed, in which only the level sums of SN ratio of significant factors appear. The optimum setting is determined by choosing the level with the highest SN ratio. Control factor A is most significant in CO, HC, and smoke than NOX. However, since factor A is less meaningful in HC, smoke emission than CO emission. So the optimum condition is A2. In respect of control factor B and C; factors B and C are significant only in HC emission and CO emission respectively. Hence B3 and C3 are predicted as the optimal levels for the parameters B and C. For factors D, F and G, more than one response is significant. So it is confirmed that D1, F2 and G3 are the optimal conditions for parameter D, F and G respectively at 40% maximum load. Same combination of parameters was obtained in a similar way for the 60% maximum load. Therefore, the optimal combinations of control factors are A2 B3 C3 D1 F2 G3 for minimized concentration of NOX, CO, HC, and smoke in the diesel engine emission both at 40% and 60% of Wmax.