LITERATURE REVIEW AND SCOPE OF RESEARCH
3.5 Experimental Procedures
Figure 3.8 Schematic of gas mixer
Figure 3.9 Fabricated gas mixer
experimental design a load level was set for engine operation. Once the engine reaches the steady-state condition, the engine was ready to present the baseline results. For this, the following data were recorded manually:
1) Engine jacket water (in/out), calorimeter water (in/out) and exhaust gas temperature, 2) The difference in liquid level in the manometer for air flow, and
3) Volume of diesel fuel consumption by the engine in one minute.
After setting the above inputs manually to the computer software program, the data were converted to engineering units and were updated and displayed on a monitor at every second.
The engine efficiency data were displayed in the form of BP, BMEP, IP, IMEP, bsfc, efficiencies, air and fuel flow rate, A/F ratio, heat balance, etc. The crank angle measurement was sensed by an optical sensor and then was acquired on a PC at time interval of two-degree CA. The engine peak cylinder pressure andP−θ diagram were recorded for each tested load.
For emission measurements, exhaust gas samples were drawn from the exhaust manifold into flue gas analyzer through a probe during the steady engine operation. The emission readings were recorded directly from the flue gas analyzer for the sample. This experimental measurement procedure was repeated for 0%, 20%, 40%, 60%, 80% and 100% engine loading. The load variations on the engine were conducted at 1500 50± rpm. The load was varied in steps by means of the eddy-current dynamometer with the help of a manually controlled knob with a digital load indicator provided in the engine controller.
3.5.2 Biogas dual fuel tests
For the biogas dual fuel operation, biogas flow was opened up slowly from gas balloon and allowed biogas to reach gas carburetor. The homogeneous air-gas mixture from carburetor was then sucked into the cylinder to take part in the dual fuel combustion via engine manifold. The amount of biogas was increased manually till engine shows signs of misfire.
This limits the maximum biogas flow for the dual fuel operation. During the process, engine speed increased due to added extra chemical energy from biogas. To maintain a constant level power and speed from both diesel and dual fuel modes, the quantity of diesel or JOME was varied by adjusting liquid fuel cut-off valve. The original and modified design of fuel cut-off valve is shown in Fig. 3.10 and 3.11 respectively. Finally, the cut-off valve was locked manually at the rated engine speed of 1500 rpm. This means that the engine operated with minimum pilot consumption at these operating conditions. Now, at a steady-state dual
fuel operation, again the same input manual parameters, as described for baseline tests, were inserted into the computer software program for efficiency and combustion results. For emission results, exhaust gas sample was examined by flue gas analyzer.
Figure 3.10 Original fuel cut-off design
Figure 3.11 Modified fuel cut-off design
3.5.3 Syngas–diesel dual fuel tests
For the syngas dual fuel operation, the H2 and CO gases were supplied from respective high pressure cylinder to an outlet pressure of about 1 to 2 bar using two-stage pressure relief valves. To avoid any possible fire hazard due to burning of H2 in presence of possible oxygen or air availability in the gas mixer, CO gas was supplied initially into the mixer followed by highly flammable H2 gas. The simulated syngas was prepared by mixing individual components of H2 and CO on a calculated volumetric ratio in the gas mixer. For an example, volumetric ratio of H2:CO is 1:1 for H2:CO ratio of 50:50 syngas. The proportion of H2 and CO in syngas was controlled throughout the dual fuel operation by adjusting the individual gas flow rate. The required flow rates of H2, CO and syngas, were achieved by manual adjustment of the control valves, and are measured separately using calibrated flow meters.
For stable operating conditions, at a set engine load, the syngas fuel valve was opened slowly and allowed the fuel-gas to enter from mixer to gas carburetor. The homogeneous air-gas mixture from carburetor was then sucked into the cylinder to take part in the dual fuel combustion. The syngas flow was increased till engine shows signs of misfire. This decided the maximum gas flow for the dual fuel operation. During the process, engine speed increased due to added extra chemical energy from gaseous fuel. To maintain the constant engine operating speed of 1500 rpm and also, to keep same power output as of 100% diesel mode, supply of diesel to the engine was reduced by adjusting diesel cut-off valve. Finally, the cut-off valve was locked manually at the rated engine speed. Now, for a steady-state dual fuel operation, again the same input manual parameters, as described for baseline tests, were inserted into the computer software program for efficiency and combustion results. For emission results, exhaust gas sample was analyzed for NOx, HC, CO and CO2 emissions from the flue gas analyzer.
Once the entire above test readings were sorted out, the normal diesel oil operation of the engine was restored by shutting gas flow and adjusting liquid fuel cut-off valve to original position. The engine was then in a position for another set of operating conditions and its experimental results starting from baseline readings. This above experimental measurement procedure was repeated as per the experimental design. At the end of whole experimental design, gas flow rate was ceased completely and the engine was made to run at a steady-state condition using only diesel at no-load condition before shut down.
3.5.4 Experiment repeatability
Experimental design was used for univariate data collection and analysis of results. The performance parameters were measured thrice as per experimental design for both diesel and dual fuel modes and averaged for each operating point. The recorded average experimental data were employed for analysis purpose.
3.5.5 Analysis procedure
The formulae used in the various performance and combustion parameter calculations of baseline and dual fuel modes were illustrated in Appendix A. The dependant variables calculated from these were analyzed and compared.
3.5.6 Uncertainty analysis
The uncertainties associated with both the diesel and dual fuel mode engine performance calculations were estimated using sequential perturbation techniques (Kline and McClintock, 1953; Moffat, 1982). The details of each measured independent parameter and also, each performance parameter overall relative measurement errors were summed up in Appendix C.
It includes contributions from individual uncertainties in measurement mass of diesel flow