Literature Review
2.3.4 Effect on Engine Performance
water (10%) has been found to be sufficient in W/O emulsion to produce lesser sedimentation (Lin and Wang, 2004b).
Figure 2.6 The separation of W/O and O/W/O emulsions for temperature variation after being motionless for a duration of 16 days (Lin and Chen, 2006a)
Figure 2.7 Effects of water contents and revolutionary speed on the sedimentation layers of the W/O and O/W emulsions (Lin and Wang, 2003)
2.3.4.2 Brake Thermal Efficiency
An experimental work with water in diesel emulsion using SPAN 80 and TWEEN 80 as surfactant with water quantity varied from 5 to 20%. It is noted that, at various engine speeds, the increase in water percentage in the emulsion increase brake thermal efficiency (BTHE) with (Abu-Zaid, 2004). This type of trend was also observed in other studies (Sawa and Kajitani, 1992; Ganesan and Ramesh, 2002). Investigation performed on two and three-phase water-diesel emulsion with water quantity varied from 10%, 15% to 20% at speeds of 1600 and 1800 rpm. The study showed a higher BTHE is obtained for W/O emulsion with 15% of water at 1600 rpm (Lin and Wang, 2004a; Lin and Chen, 2006b). However, at high speed conditions (2000 rpm to 3000 rpm), BTHE reduces with the increase in load (Armas, 2005).
A study performed by using carbon nanotubes (CNT) with 5% water emulsified diesel shows to improves engine efficiency at higher loads (Basha and Anand, 2011a). This is because at higher load condition, the CNT with its high surface area captures more heat and accelerate the ‘micro-explosion’ of water. As a result, the micro-explosion process takes place at a faster speed, which boosts the engine efficiency. Same group of authors reports similar results using alumina nanoparticles with 5% of water (Basha and Anand, 2011b).
Experimental study with emulsion of diesel and ethanol (or EMF), in the ratio of 50:50, 60:40, and 70:30 without surfactant showed a performance improvement with higher ethanol quantity (50%) (Ashok and Saravanan, 2007). The presence of higher oxygen quantity in ethanol is believed to enhance the BTHE. Again the variation of injection angles to 18°, 20°, 23° and 24° showed that at higher injection angles 50:50 diesel ethanol emulsion provides a better BTHE. This is because of the increase in rotational movement of fuel, which enhances air and fuel vapor mixing and improves efficiency. They extended their study to emulsified ethanol diesel fuel with 5% water and 6% H2O2 with the presence of hydrophilic surfactant TWEEN 80 (Ashok, 2011b). Their study shows that emulsified fuel without water shows better performance than same with water. Presence of water reduces the quantity of free oxygen in the emulsion and hence the Cetane number. The addition of dimethyl ester (DME) and diethyl ester (DEE) with 50:50 ethanol diesel emulsion have shown to increase in BTHE further than H2O2 (Ashok, 2011a). As observed in Fig. 2.8, at lower load condition water injection of 0.4 ratio shows efficiency improvement than emulsion of same water-diesel ratio.
This is because, at lower loads, the presence of water in emulsion overcools the charge against the effect of water injection in the inlet manifold.
2.3.4.3 Brake Specific Fuel Consumption
Brake specific fuel consumption (BSFC), on the other hand, seems to improve with an increases in water quantity in water diesel emulsion (Tsukahara and Yoshimoto, 1992; Abu- Ziad, 2004; Nadeem et al., 2006). As water quantity increases in emulsion, a higher amount of diesel is moved by equal amount of water. As a result a lower quantity of diesel is actually remains in emulsion. The presence of water causes finer droplet of diesel just after injection due to quick vaporization of water and results more premixed combustion. Experimental study performed by three-phase and two-phase emulsion shows that W/O emulsion always produces a lesser BSFC than O/W/O emulsion (Lin and Chen, 2006b; Lin and Chen, 2008).
The water droplets in O/W/O emulsion are larger than W/O due to the presence of another inner oil phase inside water droplets. This causes to restrict the extent of micro-explosion for a while and hence combustion of O/W/O emulsion stays a bit incomplete (Chung and Kim, 1991). This fact also reduces calorific value of O/W/O emulsion than W/O ones. However, the result of BSFC is little contrary with 20% water for water-diesel emulsion at 1800 rpm (Lin and Wang, 2004a).
As reported, the presence of CNT in water diesel emulsion reduces BSFC than without CNT (Basha and Anand, 2011b). This is because it improves thermal property of the charge thereby reducing the duration of autoignition. Hence, an increase in CNT in emulsion further reduces BSFC as observed in Fig. 2.9. Similar results are also reported for implementing alumina nanoparticle in water diesel emulsion (Basha and Anand, 2011b). The lower calorific value of ethanol causes to reduce the BSFC of the ethanol blended diesel fuel (Ashok and Saravanan, 2007). With the increase of ethanol percentage the BSFC value further reduces.
This is because increase in ethanol quantity reduces energy content of the emulsified fuel (Likos et al., 1981). Variation of injection angle (18°, 20°, 23° and 24°) of 50:50 composition of ethanol diesel emulsion causes reduction of BSFC. The lower energy content of emulsified fuel coupled with the increase in rotational movement of fuel reduces BSFC. For the same reason, the BSFC of H2O added ethanol diesel emulsified fuel run engine reduces as compared to a diesel run engine. Besides, lesser energy content of H2O2 than ethanol (Born and Peters, 1998) is also responsible of its reduced BSFC than diesel (Ashok, 2011b).
Oxygen enriched DME and DEE cause lesser fuel consumption than H2O2 added ethanol diesel emulsion fuel as described by Ashok (2011a). It is mainly because of less energy content of the esters used than H2O2. However, this result is contradictory. Because, Lin and his coworker opine that, a reduction in energy content of fuel generally increases BSFC (Lin
and Lin, 2007b). As reported by them, the presence of 10% water in O/W/O water biodiesel emulsion reduces its energy content. Hence, BSFC of emulsion is bound to increase than diesel fuel. However addition of aqueous ammonia increases the energy content of the emulsion and hence BSFC reduces.
Figure 2.8: Comparison of brake thermal efficiency with application of emulsified fuel and water injection in cylinder (Subramanian, 2011)
Figure 2.9: Variation of brake-specific fuel consumption for CNT and alumina blended water diesel emulsion (Basha and Anand, 2011a; Basha and Anand, 2011b)