PERFORMANCE AND COMBUSTION CHARACTERISTICS OF DIESEL ENGINE: METHEDOLOGY

METHEDOLOGY

Figure.1gives the details of insulated piston, insulated liner and ceramic coated cylinder head employed in the experimentation. LHR diesel engine contains a two-part piston; the top crown made of low thermal conductivity material, superni-90 screwed to aluminum body of the piston, providing a 3mm-air gap in between the crown and the body of the piston. The optimum thickness of air gap in the air gap piston is found to be 3-mm, for better performance of the engine with superni inserts with diesel as fuel.

A superni-90 insert is screwed to the top portion of the liner in such a manner that an air gap of 3mm is maintained between the insert and the liner body. At 500oC the thermal conductivity of superni-90 and air are 20.92 and 0.057 W/m-K respectively.

Fig1Performance and Combustion-1
Figure 1: Assembly Details of Insulated Piston, Insulated Liner and Ceramic Coated Cylinder Head

Experimental setup used for the investigations of LHR diesel engine with jatropha oil based bio-diesel is shown in Figure .2. CE has an aluminum alloy piston with a bore of 80 mm and a stroke of 110mm. The rated output of the engine is 3.68 kW at a rate speed of 1500 rpm. The compression ratio is 16:1 and manufacturer’s recommended injection timing and injection pressures are 27obTDC and 190 bar respectively. The fuel injector has 3 holes of size 0.25mm.

The combustion chamber consists of a direct injection type with no special arrangement for swirling motion of air. The engine is connected to electric dynamometer for measuring brake power of the engine. Alcohol is inducted through the variable carburetor jet, located at the inlet manifold of the engine at different percentages of diesel flow rate by mass basis and crude vegetable oil is injected in conventional manner. Two separate fuel tanks and burette arrangements are made for measuring vegetable oil and alcohol consumptions.

Air-consumption of the engine is measured by air-box method. The naturally aspirated engine is provided with water-cooling system in which inlet temperature of water is maintained at 60oC by adjusting the water flow rate. The engine oil is provided with a pressure feed system. No temperature control is incorporated, for measuring the lube oil temperature.

Copper shims of suitable size are provided in between the pump body and the engine frame, to vary the injection timing and its effect on the performance of the engine is studied, along with the change of injection pressures from 190 bar to 270 bar (in steps of 40 bar) using nozzle testing device.

The maximum injection pressure is restricted to 270 bar due to practical difficulties involved. Exhaust gas temperature (EGT) is measured with thermocouples made of iron and iron-constantan.

Fig2Performance and Combustion-2
Figure 2: Experimental Set-up 1. Engine, 2.Electical Dynamo meter, 3.Load Box, 4. Outlet jacket water temperature indicator, 5.Outlet-jacket water flow meter Orifice meter, 6. Piezo-electric pressure transducer, 7. TDC encoder 8.Console, 9. Pentium Personal Computer, 10. Printer, 11.Exhaust gas temperature indicator,12.AVL Smoke meter, 13. Netel Chromatograph NOx Analyzer, 14. Filter, 15.Rotometer, 16.Heater, 17. Round bottom flask containing DNPH solution, 18.Burette, 19. Variable jet carburetor, 20. Air box, 21.Orifice meter, 22. U-tube water manometer, 23.Vegetable oil tank, 24.Alcohol tank, 25. Three-way valve.

Pollution levels of smoke and NOx are recorded by AVL smoke meter and Netel Chromatograph NOx analyzer respectively at the peak load operation of the engine. With alcohol-vegetable mixture operation, the major pollutant emitted from the engine is aldehydes. These aldehydes are carcinogenic in nature, which are harmful to human beings. The measure of the aldehydes is not sufficiently reported in the literature. DNPH method is employed for measuring aldehydes in the experimentation. The exhaust of the engine is bubbled through 2,4 dinitrophenyl hydrazine (2,4 DNPH) solution. The hydrazones formed are extracted into chloroform and are analyzed by employing high performance liquid chromatography (HPLC) to find the percentage concentration of formaldehyde and acetaldehyde in the exhaust of the engine.

Piezo electric transducer, fitted on the cylinder head to measure pressure in the combustion chamber is connected to a console, which in turn is connected to Pentium personal computer. TDC encoder provided at the extended shaft of the dynamometer is connected to the console to measure the crank angle of the engine. A special P-9 software package evaluates the combustion characteristics such as peak pressure (PP), time of occurrence of peak pressure (TOPP) and maximum rate of pressure rise (MRPR) from the signals of pressure and crank angle at the peak load operation of the engine.