Thermodynamic Potential Study
8.3 Thermodynamic Potential of Emulsified POME
8.3.1 Energy Analysis
The segments of energy flows per unit time at various locations of the engine systems are expressed in Table 8.3. The average value of standard deviation is found as ±0.04. The average energy input per unit time for all the combinations of CR and IT for WIP run diesel engine is 10.95 kW. The expenditure of energy per unit time are found to be 3.22 kW, 3.50 kW, and 2.55 kW for shaft work, energy flown out through engine cooling water and exhaust gas per unit time. Finally, the uncounted energy that has been lost per unit time in the form of friction, radiation, heat transfer to surrounding etc., is recorded as 1.68 kW. Therefore, the diesel engine runs on WIP, can recover almost 30% of the fuel energy supplied in the form of shaft power. Being wasted away by various means, rest 70% of the input energy still remains unused. However, this result is certainly an improvement towards the application of emulsified POME. This is because the ratio of utilized and unutilized energy of the base fuel of WIP (POME) is found to be 26% and 74%. Table 3.4 shows that, the LHV of WIP is inferior to diesel. Nevertheless, WIP provided a higher recovery of shaft work than diesel at full load condition. The vaporization of the encapsulated water, disintegrate the POME droplets into a number of small parts. As a result, the surface area of the atomized fuel increases, which allows additional air to meet it. This leads to an enhanced fuel evaporation and turbulent mixing (Yang et al., 2013). In order to perform energy analysis, the values of various associated parameters are calculated by using the Eqs. (C1) through (C6). The variations of engine operating parameters (CR and IT) have a number of significant effect on the energy distributions (Figs. 8.10 and 8.11). The effect of CR change on the distributions has been considered by averaging the values of the three ITs, plotting and vice versa.
0.030 0.031 0.032 0.033 0.034 0.035 0.036
15.5 16 16.5 17 17.5 18 18.5
Entropy Generation (kW/K)
Compression Ratio IT (POME): 20⁰BTDC
IT (POME): 23⁰BTDC IT (POME): 28⁰BTDC
LOAD:100%
SPEED: 1500 RPM FUEL: POME
Figure 8.10 Influence of compression ratio on energy distribution for emulsified POME run engine
The percentage values of shaft works for averaged IT with respect to the fuel energy input for CRs of 17, 17.5 and 18 are 28.6%, 29.5% and 30.3%, with IT averaged. However, with averaged CR, these values are 30.86%, 29.19% and 28.36% for the ITs of 20°, 23° and 28ºBTDC. Except 18-20º (CR=18 and IT=20ºBTDC), for all other ITs, the increase in CR reduces the fuel energy input. However, unlike all other CR-IT combinations, at 18-20º WIP produces a complete 3.5 kW of rated power with a lower intake than diesel, as evident from the fuel energy input values (Table 8.3). A few researchers suggest that, the method of emulsion preparation has a significant effect on its engine performance (Lin and Chen, 2006b). The preparation of emulsion by means of ultrasonic waves, results smaller water droplets trapped inside the continuous phase (Lin and Chen, 2008). This increases the number of individual water droplets inside the fuel droplet during the high pressure atomization process of fuel injection. As the number of water droplet increases, the chances of simultaneous water bubble evaporation and more rigorous micro-explosion enhances.
Finally, the mixing of fuel air improves and leads to a better combustion performance. This is the main reason for WIP to perform better than diesel. Figure 8.12 shows the effect on BTHE for the WIP run engine as consequence with CR-IT variation. It is seen that higher the CR and more the retarded IT, higher is the BTHE. The BTHEs at 17, 17.5 and 18 CR and at retarded IT of 20ºBTDC are 26.81%, 27.47% and 27.35%, respectively. The injection of WIP at higher CR and retarded IT have allowed WIP to be injected closer to TDC, in a cylinder volume which is relatively lower than other CR-IT specifications. As a result, at the start of fuel injection, the atmosphere inside the cylinder is heated up. This enhances faster breakup of fuel droplets as water inside it will evaporate quickly. Consequently, the burning ratio is
10 15 20 25 30 35
16.8 17.0 17.3 17.5 17.8 18.0 18.3
Energy (% Fuel Input)
Compression Ratio
Qs Qw Qe Qu LOAD: 100%
SPEED: 1500 RPM FUEL: WIP
increased and the combustion is improved. This causes an increase in the percentage of shaft work with respect to fuel input at higher CR and retarded IT (Figures 8.10 and 8.11).
Figure 8.11 Influence of injection timing on energy distribution for emulsified POME run engine
Figure 8.12 Influence of compression ratio and injection timing on brake thermal efficiency for emulsified POME run engine
Figure 8.13 Influence of compression ratio and injection timing variation on peak pressure and peak heat release rate for emulsified POME run engine
10 15 20 25 30 35
18 20 22 24 26 28 30
Energy (% Fual Input)
Injection Timing (ºCA)
Qs Qw Qe Qu LOAD: 100%
SPEED: 1500 RPM FUEL: WIP
27 28 29 30 31 32
16.75 17 17.25 17.5 17.75 18 18.25
Brake Thermal Efficiency (%)
Compression Ratio IT (WIP): 20ºBTDC
IT (WIP): 23ºBTDC IT (WIP): 28ºBTDC
LOAD:100%
SPEED:1500 RPM FUEL:WIP
5 15 25 35 45 55 65 75
55 60 65 70 75 80 85 90
16.8 17.0 17.3 17.5 17.8 18.0 18.3
Peak Heat Release Rtae (J/ºCA)
Peak Pressure (bar)
Compression Ratio
IT (WIP): 20ºBTDC IT (WIP): 23ºBTDC IT (WIP): 28ºBTDC LOAD:100%
SPEED:1500 RPM FUEL:WIP
Table 8.3 Results of energy analysis for emulsified POME run engine
(± standard deviation)
Fuel CR IT Qin (kW) Qs (kW) Qw (kW) Qe (kW) Qu (kW)
Diesel 17.5 23 12.11 ±(0.09) 3.49 ±(0.07) 4.00 ±(0.11) 2.55 ±(0.08) 2.06 ±(0.17)
W
I
P
17 20 10.52 ±(0.05) 3.16 ±(0.03) 3.26 ±(0.09) 2.83 ±(0.10) 1.28 ±(0.34) 17.5 20 10.31 ±(0.07) 3.16 ±(0.03) 3.34 ±(0.06) 2.36 ±(0.08) 1.45 ±(0.19) 18 20 11.05 ±(0.00) 3.53 ±(0.08) 3.84 ±(0.08) 2.22 ±(0.15) 1.46 ±(0.17) 17 23 12.45 ±(0.11) 3.48 ±(0.07) 3.88 ±(0.09) 2.29 ±(0.11) 2.80 ±(0.39) 17.5 23 10.73 ±(0.03) 3.15 ±(0.03) 3.31 ±(0.07) 2.59 ±(0.02) 1.69 ±(0.02) 18 23 10.63 ±(0.04) 3.21 ±(0.01) 3.45 ±(0.03) 2.35 ±(0.08) 1.61 ±( 0.06) 17 28 11.05 ±(0.00) 3.06 ±(0.06) 3.32 ±(0.07) 2.64 ±(0.04) 2.02 ±(0.15) 17.5 28 10.94 ±(0.01) 3.12 ±(0.04) 3.51 ±(0.01) 2.77 ±(0.08) 1.54 ±(0.12) 18 28 10.84 ±(0.02) 3.12 ±(0.04) 3.58 ±(0.01) 2.86 ±(0.11) 1.28 ±(0.34)
The performance of WIP at higher CR can be analyzed with respect to the peak pressure and peak heat release rate curve (Figure 8.13). The CR rise from 17 to 18 increases the average value of peak pressure by 18.66% for the WIP run engine. It is reported that a rise in CR increases temperature at the end of compression stroke (Aziz et al., 2005). Both of these facts cause 34.04% rise of peak heat release rate near to TDC for WIP. However, for neat POME, the rise of peak pressure and peak heat release rate, both were approximately of 15%. This high increase of peak heat release rate shows that WIP emulsion burns with almost double intensity than neat POME near to TDC. For a constant speed engine, the presence of “micro- explosion” of emulsified POME is probably the better way to explain this fact, since at each load relative air fuel ratio should be fixed to produce same power. Alongside, it is seen that, IT advancement elevations peak pressure. Advancement of IT means that fuel is supplied at cooler atmosphere to that of retardation. Hence, fuel consumption becomes more for the same BP. It is also observed from Fig. 8.11, that the increase in CR decreases exhaust heat loss.
This is also proved from the curves of EGT (Figure 8.14). The increase of CR from 17 to 18 has reduced EGT around 15% by average. It is realized that, a fall of uncounted heat loss takes place for WIP run engine. The loss of energy per unit time (% of fuel input) which cannot be trapped are 17.6%, 14.6% and 13.4% for CR of 17, 17.5 and 18 and 13.14%, 17.80% and 14.72% for ITs of 20°,23°and 28ºBTDC. This is a reasonably definite drop, which can be achieved with the increase of exhaust energy loss per unit time.