CHAPTER-2
2.3 Fuel Modification Technique
2.3.2 Diesel engines fueled with Preheated Biodiesel
Some of researcher had successfully studied on direct use of biodiesel oil and its blends in a diesel engine for short term, the long-term endurance tests reported durability issue of the engine such as severe engine deposits, piston ring sticking, injector coking, gum formation and lubricating oil thickening (Agarwal and Agarwal, 2007). The biodiesel oils cannot be used directly without
bringing its properties closer to petroleum fuel as diesel. Mainly viscosity reduction is sufficient to improve its flow and atomization properties. The researchers were adopted different methods in a diesel engine to improve the performance biodiesel such as preheating, blending with diesel, blending with oxygenated additives and alcohols (Jain et al., 2011; Jeryrajkumar et al., 2016;
Rajagopal et al., 2015; Senthil et al., 2015a). Among them, preheating of neat biodiesel oil is one of the simple and cost effective methods to reduce the cold flow problems and improve the performance and emissions (CO and HC) with an increase of NOx emission of an engine (Ibrahim et al., 2014; Mustaffa et al., 2014a; Venkata Ramanan and Yuvarajan, 2015). There have been some investigations on using preheated neat biodiesel in diesel engines.Nasim et al. (2013), performed experimental investigation on compression ignition engine powered by preheated neat Jatropha oil. In his study, the high viscosity of the Jatropha curcas oil was decreased by preheating.
The effect of fuel inlet temperature on performance of diesel engine is evaluated and the results shows drop in BSFC with increase in fuel inlet temperature of Jatropha oil.Pradhan et al. (2014), worked on combustion and performance of a diesel engine with preheated Jatropha curcas oil using waste heat from exhaust gas. Helical coil heat exchanger is used to utilize the heat of exhaust gases for preheating CJO which reduces its density and viscosity. The BSFC and ignition delay period were decreased while BTE increased with increase in engine load. The fuel properties were improved by preheating and it can be used in the diesel engines without any modification as a substitute for diesel. Rahim et al. (2012), worked on influence of fuel temperature on a diesel engine performance operating with biodiesel blended. The effect of fuel temperatures on variation engine speed and their impact on the engine performance of a four-cylinder diesel engine has been investigated. In his result it can be found that the highest fuel temperature causes the highest injection pressure thus resulting in shorter ignition delay. The shorter ignition delay attributed to the early start of combustion thus leads to the higher in-cylinder pressure. The increase of fuel temperature represent the highest energy content thus resulted in lower BSFC as obviously desired.
Kadu and Sarda (2010), investigate the use of preheated neat karanja oil in CI engine. The engine used for experiment was 4 stroke, single cylinder CI engine by preheated blend from 30-100 °C and speed between 1500-4000 rpm. Various parameters like BTHE, BSFC, emissions were compared. The result showed that SFC was higher compared to diesel for all loads. Hossain and Davies (2012), worked on the indirect injection CI engine which uses neat jatropha and karanj oil as fuel. Modifications were done on the cooling water circuit and fuel supply system such that
jacket water was preheated. BSFC increases 3%, CO2& NOx increases by 8%, as compared to diesel. From this it is concluded that the IDI compression ignition engine can be used with pure preheated Jatropha oil by jacket water. Chauhan et al. (2010), worked on performance enhancement of diesel engine by preheating technique while using Jatropha oil as a fuel. The aim is to decrease the viscosity of fuel using EGR system. Shell and tube type heat exchanger was used to preheat the fuel before entering to the engine which reduce the viscosity of blend. From results it was concluded that preheated blend having high BTHE and low BSEC at 80°C for optimum use of Jatropha oil. Karabektas et al. (2008), reported that the specific gravity and kinematic viscosity of the COME gradually decrease with the increase in the preheating temperature. Tests were carried out at full load conditions in a one-cylinder, four-stroke, direct injection diesel engine.
Before supplied to the engine, COME was preheated to four different temperatures, namely 30, 60, 90 and 120 °C. It is seen that the kinematic viscosity is 6.54 cSt at 30 °C and decreases gradually to 1.26 cSt at 120 °C. Additionally, the specific gravity decreases from 0.882 at 30 °C to 0.851 at 120 °C. The results revealed that preheating COME up to 90 °C leads to favorable effects on the BTE and CO emissions but causes higher NOx emissions. Moreover, the brake power increases slightly with the preheating temperature up to 90 °C. When the COME is preheated to 120 °C, a considerable decrease in the brake power was observed due to the excessive fuel leakage caused by drop in fuel viscosity. The results suggest that COME preheated up to 90 °C can be used as a substitute for diesel fuel without any significant modification in expense of increased NOx
emissions. Chauhan et al. (2010), worked on performance enhancement of diesel engine by preheating technique while using Jatropha oil as a fuel. The aim is to decrease the viscosity of fuel using EGR system. They found that the BTE (brake thermal efficiency) of engine was lower and BSEC (brake specific energy consumption) was higher when the engine was fueled with Jatropha oil as compared to diesel fuel. Increase in fuel inlet temperature resulted in increase of BTE and reduction in BSEC. Emissions of NOx from Jatropha oil during the experimental range were lower than diesel fuel and it increases with increase in fuel inlet temperature. The CO (carbon monoxide), HC (hydrocarbon), CO2 (carbon dioxide) emissions from Jatropha oil were found higher than diesel fuel. Kadu and Sarda (2010), investigated the use of preheated neat karanja oil in CI engine.
The engine used for experiment was 4 stroke, single cylinder CI engine by preheated blend from 30-100°C and speed ranges 1500-4000 rpm. Various parameters like brake power, thermal efficiency, BSFC, emissions were compared. Result shows that SFC was higher compared to diesel
for all loads. Hossain and Davies (2012), worked on the indirect injection CI engine which uses neat Jatropha and Karanj oil as fuel. Modifications were done on the cooling water circuit and fuel supply system such that jacket water was preheated. BSFC increases 3%, CO2& NOx increases by 8%, as compared to diesel. From this it is concluded that the IDI compression ignition engine can be used with pure preheated Jatropha oil by jacket water. Shivaji and Gowreesh (2014), worked on the Pongamia biodiesel preheated to 80°C to study the effect of preheating of biodiesel on engine characteristics. The performance characteristics like total fuel consumption, brake specific fuel consumption, brake specific energy consumption, brake thermal efficiency and the combustion characteristics like variation in cylinder pressure and net rate of heat release are investigated. The engine characteristics are also investigated with preheated biodiesel at injection opening pressure of 200, 220 and 240 bars and at CRs of 17, 17.5 and 18. Improvement in engine characteristics is observed by preheating the biodiesel. Among different injection opening pressure and compression ratios, highest brake thermal efficiency was obtained at 200 bars and 18 compression ratios respectively. Martin and Prithviraj (2011), investigated, the viscosity of cottonseed oil (CSO) by blending it in different proportions with diesel, and its viscosity at various temperatures was analyzed. Then, they are used as a fuel in a CI engine. Performance, combustion and emission parameters at various loads were calculated using a single cylinder CI engine and compared with neat diesel and cottonseed oil. A remarkable improvement in the performance of the engine is noticed as the viscosity of the oil is reduced. Brake thermal and volumetric efficiencies of the engine increased with a significant reduction in the exhaust gas temperature.
Reductions in smoke, CO and HC emissions are also noticed. Results show that a blend containing 60% of cottonseed oil with diesel, which is heated to a temperature of 70°C, can be used as an alternate fuel without any engine modification. Augustine et al. (2012),investigated the effects of preheated cottonseed oil methyl ester on performance parameters on a single cylinder diesel engine (660 cc). They concluded that BSFC is higher than that of diesel engine for all loads tested. This was due to more blended fuel which is used to produce same power as compared to diesel fuel.
Moreover, brake thermal efficiency was lower than diesel fuel but increased by the preheated temperature ranging from 40°C up to 80°C, beyond 100°C there is vapor locking in the fuel line and hence more fuel consumption is noticed for the same power compared to other mode of operation. Results also shown that, preheated cottonseed oil methyl ester caused to lower the CO, unburned HC and smoke compared to diesel fuel. This were attributed to the higher O2 content of
biodiesel which could improve the combustion process and heating process decreases the viscosity of biodiesel, thus improves the oxidation of biodiesel in the cylinder. However, preheated cottonseed oil methyl ester yields higher NO, emission at all loads than that of diesel fuel. Yilmaz and Morton (2011), studied the performance of three vegetable oils at two different engines Yanmar and Kubota engines. Brake thermal efficiency, exhaust gas temperature, and CO, O2, Unburned HC and NO emissions are determined as a function of load at ambient and preheat conditions for peanut, sunflower and canola oils. They found that preheating increases thermal efficiency and vegetable oil shows higher thermal efficiencies than diesel fuel for all of the preheated fuels and both engines. Vedharaj et al. (2015), investigated the performance emission and economic analysis of preheated CNSL biodiesel as an alternate fuel for a diesel engine.
Preheating the biodiesel reduced the viscosity, and the performance and emission of preheated CNSLME has been improved. At an inlet fuel temperature of 80◦C, the CNSLME discerns a 20%
increase in BTE (brake thermal efficiency), 66% and 52% decrease in CO and HC emission, respectively than unheated CNSLME. To purport the economic viability of CNSL, a detailed economic analysis has been conducted.