Results and Discussion: Preheated Biodiesel Blends Run Engine
6.3 Result and Discussion
6.3.2 Effect of Preheated Biodiesel Blends on Engine Performance Parameters
Figure 6.3: Variation of calorific value with percentage of preheated POME biodiesel blends.
6.3.1.5 Optimum Preheated Blending Ratios
When preheated biodiesel is blended with diesel the characteristics of the new fuel changes as per the volumetric percentage of biodiesel in a mixture of biodiesel and diesel. The blending ratio will be optimum when the blended fuel will satisfy the different standards as specified by the different countries.Accordingly, an optimum blending ratio was recommended for the POME at the ratios of 20% to 60% according to the properties of the POME−diesel blends. The optimal blends (PPBD20−PPBD60) would have the kinematic viscosity of 3.38 mm2/s to 4.08 mm2/s and density of 851 kg/m3 to 863 kg/m3 which comply with the limits of the blended biodiesel standard specifications. The calorific value (43.12 MJ/kg −41.67 MJ/kg), flash point (103 °C−181°C) and pour point (-1°C to 4 °C) are above the lower limit (35 MJ/kg, 52 °C and 3 max.), respectively. So an optimum blending ratio of up to 60% blending (up to PPBD60) has been recommended by compliance of the preheated biodiesel-diesel blend specification to the specified standards, which can be used in diesel engines without modification and without sacrificing much power loss.
two phases for each performance parameters (BSFC, BTHE, EGT, and volumetric efficiency). In the first phase, tests were carried out at varying engine loads (0%−100%) with 20% increments without EGR rate, and results of various preheated biodiesel blends were compared with diesel. In second phase, similar experiments were performed at varying EGR rates (10%−40%) in steps of 10% under full engine load, and the results were compared to with no-EGR operating conditions.
Accordingly, an optimum blending ratios were recommended for the preheated POME biodiesel blends, for the considerable utilization of high blend ratios of preheated POME biodiesel as a fuel in a diesel engine. The results of the experiments are presented in the following sub-sections.
6.3.2.1 Effect of Preheated Biodiesel Blends on BSFC
Figure 6.4(a) shows the effect of preheated POME biodiesel/diesel blends on BSFC as a function of engine load without EGR. It is seen in BSFC all tested fuels gradually decreases with increasing engine load in a similar trend as mentioned in references (Chauhan et al., 2010; Rambabu et al., 2013). It is mainly due to better combustion characteristic due to improved fuel-air mixing rate at high engine loads. At full load and with respect to PPBD100, the average reduction of BSFC for PPBD20, PPBD40, PPBD60 and PPBD80 was found to be 32.74 %, 28.79 %, 17.78 % and 10.14
%, respectively. It can be seen BSFC increases with increase in preheated POME biodiesel quantity in the blend as more amount of blends are required to produce the same amount of power by the engine due to the less energy content of POME biodiesel when compared to diesel fuel. It clearly indicates that PPBD20−PPBD60 offered better BSFC compared to other tested fuels. With respect to pure diesel (PBD0), the BSFC is seen to be 7.8%, 11.1% and 21.5% higher for PPBD20, PPBD40 and PPBD60.
The effect of increasing EGR rates on BSFC for preheated POME biodiesel/diesel blends at full engine load is presented in Figure 6.4(b). BSFC generally increases for all preheated POME biodiesel /diesel blends at increasing EGR rates with the consumption being more for PPBD60 blends (Kegl et al., 2013; Qi et al., 2009). This is because of the reduction in oxygen availability in cylinder for combustion, which leads the reduction in in-cylinder temperature due to the application of EGR leading to incomplete combustion. It is indicated that BSFC for PPBD100 is higher for every EGR rates as compared to other tested fuels. This is because of reduction in in- cylinder gas temperature due to higher oil viscosity leading to incomplete combustion. However, BSFC for PPBD20 to PPBD60 are seen to be decreased as compared to other test fuels. Thus, it
offers improved fuel properties, increased in-cylinder temperature, better air-fuel mixing process and combustion characteristic.
(a) (b)
Figure 6.4: Variation of BSFC: (a) With loads (no-EGR); (b) With EGR rates at full load.
6.3.2.2 Effect of Preheated Biodiesel Blends on BTHE
By referring to Figure 6.5(a), the BTHE, show opposite trends with respect to BSFC. It shows the effect of preheated POME biodiesel/diesel blends on brake thermal efficiency as a function of engine load without EGR. It can be seen that BTHE increase with engine load but decreases slightly from 90% to 100% loads. This slight drop could be due to the low excess air ratio at high engine loads that worsened the combustion (Heywood, 1988). It can be seen that preheated POME biodiesel/diesel blends have lesser BTHE than diesel. Increasing preheated POME biodiesel fraction in the blend caused a drop in BTHE due to the less energy content of POME biodiesel when compared to diesel fuel. A maximum drop of BTHE for PPBD20, PPBD40, PPBD60 and PPBD80 were 22.67%, 17.86%, 12.2% and 5.2%, respectively as compared to PPBD100 at full engine load. Thus, it is understood that, BTHE for POME was significantly improved with a combined effects of heating and blending with diesel fuel. Relating to neat diesel (PBD0), the BTHE of PPBD20, PPBD40 and PPBD60 was lower 2.16%, 6.0% and 10.5%. Hence, PPBD20, PPBD40 and PPBD60 test fuel offers the most efficient BTHE as compared with other tested fuels.
(a) (b)
Figure 6.5: Variation of BTHE: (a) With load (no-EGR), (b) With EGR rates at full load.
The effect of increasing EGR rates on preheated POME biodiesel/diesel blends at full engine load (12 kg) was presented in Figure 6.5(b). It can be see that BTHE decreases very slightly for all preheated POME biodiesel/diesel blends at increasing EGR rates (Agarwal et al., 2011;
Saravanan, 2015). Increase in EGR impedes the normal combustion process and reduces the burning rate. The increase of the percentage of exhaust gas recirculated to the engine threatens the normal engine combustion process because it decreases in-cylinder gas temperature along with oxygen deficiency. The average percentage decrements of BTHE for PPBD20, PPBD40 and PPBD60 test fuel at 30 % EGR rate were 6.53%, 7.36% and 6.75%, respectively as compared to no-EGR rate (0%EGR). However, at 40% EGR rate the BTHE for different blends of fuels are found decreased significantly as compared to no-EGR rate, thus BTHE at 30% EGR rate for PPBD20−PPBD60 test fuel found to be the optimum as compared to no-EGR rate studied in these investigations.
6.3.2.3 Effect of Preheated Biodiesel Blends on EGT
Another performance indicator of the fuel quality during combustion process is the EGT. Figure 6.6(a) shows the variation of exhaust gas temperature as function of engine load under no-EGR. It can be seen that exhaust gas temperature increases with increasing preheated POME biodiesel content in the blend. It essentially means fuel energy has been efficiently used at higher loads
because of improved oil quality and the presence of oxygen content in biodiesel. It is seen that all the test fuels of POME have higher EGT as compared diesel. The higher value of EGT implies increased in-cylinder gas temperature and thus ensures efficient combustion characteristics of the fuel. Since the biodiesels have higher Cetane numbers, the premixing time reduces and combustion phasing moves earlier towards the compression stroke. In addition, the occurrence of higher oxygen content in POME facilitates better combustion and causes EGT to be higher. The earlier experimental findings do highlight similar results (Pradhan et al., 2014). In general, the preheating ensures higher EGT but with lower blending ratio, the EGT drops with heating. At full load condition, the overall increase of EGT for PPBD100, PPBD80, PPBD60, PPBD40 and PPBD20 were, 20.54 %, 16.84%, 12.93 %, 9.9% and 8.03 %, respectively, as compared to diesel (PBD0) even though it has higher calorific value.
(a) (b)
Figure 6.6: Variations EGT (a) With load (no-EGR), (b) With EGR at full load.
Figure 6.6(b) shows effect of increasing EGR percentages on exhaust gas temperature for all preheated biodiesel/diesel blends at full engine load. It can be seen that the exhaust gas temperature slightly decreases in EGR rates for all blends as a result of oxygen in combustion chamber and reduction in peak combustion temperature brought about by the increase of EGR conditions (Agarwal et al., 2011; Saravanan, 2015). At EGR 40%, the overall reduction of EGT is about 25% for all test fuels as compared to EGR0% (without EGR).
6.3.2.4 Effect of Preheated Biodiesel Blends on Volumetric Efficiency
Figure 6.7(a) illustrate the effect of preheated POME biodiesel/diesel blends on the volumetric efficiency with variation of loads under no-EGR. For all fuels, it drops slightly with increase of loads (Rambabu et al., 2013). This is because of increased in-cylinder gas temperature at higher engine load leading to higher gas pressure in the cylinder. Hence, it restricts the air quantity at inlet of the engine cylinder resulting slightly drop of the volumetric efficiency of the engine with increasing load. The effect of preheating POME helps to improve volumetric efficiency of diesel engine. The heated POME blend fuels causes improvement in fuel injection characteristics and combustion efficiency leading to increased amount of air intake. Due to this fact, there is a slight increase of volumetric efficiency, but it is still somehow lower than the mineral diesel fuel. At 100% loading condition, the average value of volumetric efficiency is about 80 % for all test fuels including diesel. The variations of volumetric efficiency for different fuels with EGR rates at full engine loading condition is shown in Figure 6.7(b). All the test fuels show marginal drop (2.5 %) with increasing the EGR rates which is in line with reported literatures (Agarwal et al., 2011). It is mainly due to the reduction of amount of intake air mass flow into engine cylinder for combustion and supply of exhaust gases to in the engine cylinder through EGR system.