Results and Discussion: Preheated Biodiesel Blends with Intake Air Preheating Mode Run Engine
7.2 Materials and methodology
7.2.1 Experimental Facilities
Tests were performed considering a modified experimental setup demonstrated in Figure 3.13.
Table 3.1shows the specification of the engine. For preheating intake air, we have developed a novel shell and tube counter flow type heat exchanger which is located at the air inlet, and it preheat the combustion air to the required temperature for ignition of fuel. In the modified experimental set up, along with intake preheater, a helical coiled type heat exchanger is also integrated for heating the biodiesel (refer Figure 3.13). The detailed technical specifications each preheater are given in Table E.1(Appendix-E). Both the heat exchangers are indigenously designed with an assumption to meet the requirements with specific intended purpose. While designing a fuel and
intake air preheater, the laws, which govern this process, should be well understood and thus should be used in this design, construction, testing and operation of the equipment. The intake air and biodiesel were preheated by engine exhaust gas temperature, when it is passed through a newly designed preheating systems. An exhaust gas analyzer (AVL-444 DI-GAS, India) was used for emissions of HC, CO, CO2 and NOx measurement. Finally, the experiments with all the fuel samples in the diesel engine are conducted to study combined impact of air and fuel preheating on the engine performance, combustion and emission characteristics under stable conditions of operation at constant speed (1500 rpm) with default CR 17.5, 200 bar and 23° bTDC of fuel IP and IT, and are shown in test matrix Table 3.3. For each test (PBD0, PPBD20, PPBD40, and PPBD60), important observations such as, mass flow rate of fuel, mass flow rate of air, temperatures, temperatures at various locations and emission measurements (CO, HC, CO2, and NOx) were made. The best operating condition for each blends of was calculated/measured (BSFC, BTHE, cylinder pressure, heat release rate, PCP and ID, and finally the optimum condition (intake air preheating temperature) for the operation of CI engine was determined.
7.2.2 Methodology
While executing the tests, the supply of exhaust gas to both preheating device (fuel and intake air preheaters) is regulated in combination to a manual control gate valves (gv2 and gv3) so that preheat temperatures in both devices are properly controlled (refer Figure 3.13). The operation of fuel preheater (Hx1) is controlled manually by two valves “gv1 & gv2” and both are regulated in combination to control exhaust gas flow rate so that the preheat temperature is properly set. When the engine starts, the valve (gv2) is fully open while valve (gv1) is closed partially to restrict exhaust flow to the atmosphere. It allows major quantities of the engine exhaust gases to come in contact with the surface of helical coil. Once the required temperature is displayed in a digital temperature gauge instrument, the opening of valves (gv2) is manually decreased. Subsequently, increasing the opening angle of valve (gv1) allows more exhaust gas flow to atmosphere such that the exhaust gas supply get restricted in order to maintain constant temperature of fuel. When the temperature drops below the necessary value, the opening of the valve for “gv2” is increased and for “gv1”, it is decreased to execute other heating process. This POME (biodiesel) with elevated temperature then flows through secondary fuel pipe (made of the same material as that of fuel injection line) and then connected to the fuel blend metered glass burette. The blending of different percentage fractions of biodiesel with diesel was done manually based on the percentage in volume
requirements of preheated POME using a biodiesel and diesel fuel flow control two-way valves (v1 and v2) as shown in Figure 3.13. Once proper blend ratio achieved, both valves, (v1 and v2) were closed and the enginegets fuel from the metered glass burette through valve “v3”.
Similarly, an intake air preheater (shell and tube type) device, (Hx2) has been arranged in the modified experimental setup as shown in Figure 3.13. It is not fixed directly in exhaust gas line rather adequate distance is maintained closure to intake manifold. The heating device is kept, as close as possible to the inlet openings of the cylinders. This arrangement assists the intake air combustion is taken from the atmosphere through an air filter (refer Figure 3.13). The filtered air is passed through the copper tubes in the intake line surrounded with the exhaust gases in the shell.
This arrangement guarantees fast heating of the intake air as well as increased robustness and simplified mounting. The operation of preheater is similar to that of a fuel-preheater, for which the flow exhaust gas temperature to intake air preheater is controlled manually by using two valves (gv1 and gv3) as shown in Figure 3.13. While executing the tests, both are regulated in combination to control exhaust gas flow rate so that preheat temperatures in both devices are properly controlled. The operating intake air preheating temperatures (from atmospheric temperature of (33 °C to 41°C, 49 °C and 61°C) and fuel preheating temperature (114 °C), were decided based on optimal engine operations at constant 90% (10.8 kg) of engine load. The experiments were carried out with a standard operating conditions (CR 17.5, fuel IP of 200 bar, fuel IT of 23° bTDC) at 90% engine load without EGR. It may be emphasized here that a diesel engine has better fuel combustion and the effective conversion of chemical energy into useful work. In most of diesel engine, in the range of 80−90% of full load, the engine has the maximum thermal efficiency, but increasing to 100% of full load, the thermal brake efficiency decreases because the engine reaches the smoke limit (Najafi et al., 2018). All diesel engines attain best performance including specific fuel consumption and thermal efficiency at rated power. For a constant speed for four stroke diesel engines operated in the range of 80-90% load, the general tendency is that specific fuel consumption (fuel consumption per unit brake power) decreases efficiently. Beyond this load (> 90%), it gradually increases, thereby, the effectiveness to convert the chemical energy contents of fuel into useful work drops leading to decrease of mechanical efficiency and increase of radiation losses (un accountable losses) and frictional losses. That is why, in this experimental study, the full load (100%) engine loading operating condition was not considered so as to avoid the exhaustion and failure of the engine as a precautionary measure.