Studies on the use of low-volatile non-edible oils in a thermal barrier-coated diesel engine

Abstract

Owing to the ever-increasing vehicle population, the consumption of diesel fuel in the transportation, agricultural and industrial sectors has increased at an alarming rate. This has led to rapid fossil fuel depletion, ozone depletion and environmental degradation, which have become a serious concern. Search for alternative renewable and clean energy fuel sources to mitigate the emissions of greenhouse gases is continuing, and attempts to find different techniques for efficient utilization of these fuels are also undertaken. Biodiesel being an oxygenated fuel obtained from vegetable oils has received greater attention over the years as a promising alternative to diesel fuel. However, vegetable oils exhibit high viscosity, poor volatility and poor cold-flow characteristics. These characteristics can cause the following problems in the engine when run for a longer duration: injector coking, severe engine deposits, filter gumming, piston ring sticking and thickening of lubrication. These problems can be eliminated or minimized by adopting suitable fuel processing techniques to obtain biodiesels from vegetable oils. The fuel processing techniques vary widely, which include transesterification, supercritical methanolysis, ultrasonic and continuous microwave-assisted transesterification methods. In the present study, the transesterification method is effectively used to obtain biodiesels from non-edible oils of honne and cotton seed. The biodiesels obtained from these oils were used in the unmodified diesel engine to check their feasibility as diesel engine alternatives. Different thermal barrier coatings (TBCs) were applied on the piston, cylinder head, and inlet and exhaust valve surfaces of the diesel engine in order to make it a fully adiabatic engine. The engine with such TBCs is called a low heat rejection engine. For the present study, the TBC of partially stabilized zirconia (PSZ) and aluminium oxide (Al₂O₃) were selected. Finally, the performance of the diesel engine fuelled with different biodiesels in both conventional and thermal barrier-coated modes was compared. The thermal barrier-coated engine with the PSZ version showed better performance with increased nitric oxide emissions when compared with the Al₂O₃ coating.

Keywords::

• diesel engine
• LHR engines
• PSZ coating
• biodiesel
• emissions
• combustion parameters
• heat release rate

1. Introduction

Energy derived from renewable and alternative fuels is an essential input for the economic growth of any country (Banapurmath 2011). In this context, it is quite essential to use alternative fuels as their use are greatly influenced by the factors such as energy security, environmental concerns, foreign exchange savings and socio-economic issues. (Ayhan 2007). The importance of alternative fuels was recognized in the early 1900s by Dr Rudolph diesel. The promotion of alternative fuels such as vegetable oils for a compression ignition (CI) engine has gained sustained attention. Currently, it is estimated that India will be able to produce 288 metric tons of biodiesel from a variety of vegetable oils by the end of 2012 (Yaliwal et al. 2010). This in turn can supplement about 41.14% of the total demand of diesel fuel consumption of the country (Ashok and Saravanan 2005). India has one of the largest programmes for alternative fuels that cover the entire relevant fuel technologies such as biodiesel, biogas, bioethanol and producer gas. Global demand for biodiesel has increased from 6.9 to 44.8 million tons during the periods 2006 and 2010 (Yaliwal et al. 2010). In view of this, research has mainly focused on the use of vegetable oils in general and non-edible oils in particular as suitable alternative fuels. Non-edible oils derived from plant seeds are renewable, environment friendly, non-toxic and biodegradable, and they contain no sulphur and aromatic contents and are most promising alternative fuels for a CI engine (Agarwal and Rajamanoharan 2009; Ashok and Saravanan 2005; Babu and Devardjane 2003; Banapurmath et al. 2005; Ghadge and Raheman 2005). Various non-edible oils such as honne, cotton, Honge, neem, mahua and jatropha oils are abundantly available in India, and their respective biodiesels are an alternative to diesel fuel.

Non-edible oils pose some problems when used directly in an engine as a diesel substitute (Agarwal and Agarwal 2007; Banapurmath et al. 2008; Canakci 2005; Emil et al. 2009; Ertan and Canakci 2009; Hosmani, Hiremath, and Keri 2009; Narayana Reddy and Ramesh 2005; Recep, Selim, and Huseyin 2000). These problems can be solved if neat vegetable oils are chemically modified to their respective biodiesels that are similar in characteristics to diesel fuel (Alessandro et al. 2009; Banapurmath and Tewari 2008; Mahanta, Mishra, and Kushwash 2006). Differences in the molecular structure of oils greatly influence the physical and chemical processes occurring during the atomization, vaporization, spray pattern and combustion of the fuel when injected into the combustion chamber (Lertsathapornsuk et al. 2005). The presence of fatty acids in vegetable oils greatly affects diesel engines when used directly. The different fatty acids present in vegetable oils are palmitic, stearic, lignoceric, oleic and linoleic acids (Amman 1988; Ekrem, Tahsin, and Muhammet 2006; Jaichandar and Tamilporai 2003). These fatty acids in vegetable oils increase smoke emissions and also lead to incomplete combustion due to improper air–fuel mixing. Proper fuel processing or transesterification of vegetable oils can reduce viscosity and increase the cloud and pour points of biodiesels.

The major drawback of the use of biodiesel is its higher viscosity (nearly twice its counterpart diesel fuel) and lower volatility. The use of adiabatic engines is one solution to effectively combust biodiesels in diesel engines. Many studies on the application of the adiabatic or low heat rejection (LHR) concept by using biodiesels in standard diesel engines can be found in the literature (Agarwal and Agarwal 2007; Ahmaniemi et al. 2004; Amman 1988; Banapurmath and Tewari 2008; Banapurmath, Tewari, and Hosmath 2008; Ekrem, Tahsin, and Muhammet 2006; Jaichandar and Tamilporai 2003; Sun et al. 1993). Various thermal barrier coatings (TBC) of silicon carbide, silicon nitride, aluminium titanate, aluminium magnesium silicate and ceramics such as aluminium oxide (Al₂O₃) and partially stabilized zirconia (PSZ) have been used. PSZ has been found to be quite desirable for adiabatic engine applications due to its excellent insulating characteristics, strength and thermal expansion characteristics. They are coated on the surfaces of the piston, cylinder head, cylinder liner, and inlet and exhaust valves. The coating thickness varies from 1 to 2 mm. There are some important advantages of coated LHR engines: improved fuel economy, reduced engine noise and multi-fuel capability using low-cetane biodiesel fuels (Agarwal and Agarwal 2007; Ahmaniemi et al. 2004; Banapurmath and Tewari 2008; Banapurmath, Tewari, and Hosmath 2008).

A large number of studies on the performance, structure and durability of the LHR engine have also been reported (Hergart 2001; Narayana Reddy and Ramesh, 2005). However, the results of these investigations are contradictory. Most of these studies have concluded that insulation reduces heat transfer, improves thermal efficiency and reduces exhaust emissions. However, some experimental studies have indicated almost no improvement in thermal efficiency and claimed that exhaust emissions deteriorate when compared with conventional diesel engines.

In the present study, engine combustion chamber elements such as piston, cylinder head and valve faces were coated with two types of TBC such as PSZ and Al₂O₃. A comparison was made to study the performance and emission characteristics of the engine when coated with two different coatings and with normal uncoated engine fuelled with biodiesels derived from honne and cottonseed oils.

2. Properties of the test fuels

For the present study, non-edible oils derived from honne and cotton seed were selected. These oils were transesterified to obtain their respective biodiesel fuel. Biodiesel from cotton seed oil was extracted according to the following procedure: 1 litre of raw cotton seed oil was heated and maintained at a temperature of 65°C for 30 min to remove moisture content. Then, the oil was titrated against the NaOH solution, which showed about 1% free fatty acids. The moisture-free cotton seed oil (1 l) was heated to a temperature of 55°C in the flask. Then, a mixture of 200 ml methanol and 4 g NaOH was added. The resulting mixture was maintained at the same temperature with a stirrer speed of 400 rpm. After 1 h, the mixture was allowed to settle in a separating funnel for 8 h. Finally, the heavier layer of glycerin was separated out to obtain the biodiesel, which was washed three or four times with a 10 ml acetic acid+hot water solution to remove moisture content and other sediments. The clean cotton oil methyl ester was thus obtained. The yield of the resulting ester was about 94%.

The fuel properties of the biodiesel and non-edible oils and their respective biodiesels were measured in the laboratory. The properties of these oils are shown in Table 1.

Table 1 Properties of the fuels used.

Properties	Diesel	Cotton seed oil	COME	Honne seed oil	HnOME
Chemical formula	C13H24	–	–	–	–
Density (kg/m^3)	840	900	885	910	880
Calorific value (kJ/kg)	43,000	38,049	39,648	39,100	39,798
Viscosity at 40°C (cSt)	2–5	50	5.00	32.48	4.5
Flash point (°C)	75	210	167	228	187.5
Cetane number	45–55	48	45	51
Carbon residue	0.13	0.55	0.01	0.01	0.01
Cloud point (°C)	− 2	–	7	− 2.5	− 1
Pour point (°C)	− 5	–	4	− 0.8	− 8
Molecular weight (kg/kg mol)	181	–	227	–	–
Autoignition temperature (°C)	260	–	470	–	–
Ash content (% by mass)	0.57	–	0.01	–	–

3. Experimental set-up

The overall view of the experimental set-up is shown in Figure 1. The engine tests were conducted on a four-stroke, single-cylinder, direct-injection, water-cooled CI engine. The specifications of the engine are given in Table 2. The engine was operated at a rated speed of 1500 rpm. The engine had a conventional fuel injection system. According to the manufacturer's specification, the injection nozzle used for the diesel had three holes of 0.3 mm diameter with a spray angle of 120° apart and an injector opening pressure of 205  bar along with a static injection timing of 23° before top dead centre (bTDC). The nozzle used for the biodiesel had four holes of 0.3 mm diameter with a spray angle of 90° apart and an injector opening pressure of 230  bar along with a static injection timing of 19° bTDC. The regular governor of the engine was used to control the engine speed. The engine was equipped with a hemispherical combustion chamber having overhead valves that were operated via push rods. The engine was cooled by the circulating water that flowed through the jackets of the engine block and cylinder head. The experiments were conducted at an inlet cooling water temperature of 80°C under a steady-state thermal condition. A piezoelectric pressure transducer was mounted flush with the cylinder head surface to measure the cylinder pressure.

Figure 1 Overall view of the experimental setup with EGR arrangement. 1 – Control Panel, 2 – Computer system, 3 – Diesel flow line, 4 – Air flow line, 5 – Calorimeter, 6 – Exhaust gas analyzer, 7 – Smoke meter, 8 – Rota meter, 9, 11 – Inlet water temperature, 10 – Calorimeter inlet water temperature,12 – Calorimeter outlet water temperature, 13 – Dynamometer, 14 – CI Engine, 15 – Speed measurement,16 – Burette for fuel measurement, 17 – Exhaust gas outlet, 18 – Outlet water temperature, T1 – Inlet water temperature, T2 – Outlet water temperature, T3 – Exhaust gas temperature.

Table 2 Specifications of the engine.

Make and Model	Kirloskar, TV1
No. of cylinders	One
Orientation	Vertical
Cycle	4 Stroke
Ignition system	Compression ignition
Bore X Stroke	87.5 mm X 110 mm
Displacement volume	660 cc
Compression ration	17.5:1
Arrangement of valves	Overhead
Combustion chamber	Open chamber (Direct Injection)
Rated power	5.2 kW (7 HP) @1500 rpm
Cooling medium	Water cooled

Exhaust gas opacity was measured using the Hartridge smoke opacity meter. Exhaust gas emissions were measured using an exhaust gas analyser (Make: MRU, Model: Delta 1600S). Figures 2 and 3 show the piston and cylinder head coated with PSZ and Al₂O₃, respectively, to obtain an LHR engine.

Figure 2 Piston and cylinder head coated with PSZ.

Figure 3 Piston and cylinder head coated with Al₂O₃.

4. Results and discussion

The experiments were conducted on the direct-injection CI engine with PSZ and Al₂O₃ ceramic coatings. Baseline readings were also generated for the existing uncoated diesel engine for a comparative study. The engine was fuelled with honne oil methyl ester (HnOME) and cotton seed oil methyl ester (COME) in both the coated and normal diesel engine operations.

4.1 Performance parameters

4.1.1 Brake thermal efficiency

The effect of brake power on brake thermal efficiency (BTE) for diesel, HnOME and COME in the normal engine operation is shown in Figure 4. It can be observed that there was a steady increase in BTE as the load increased for the diesel, HnOME and COME operations. The BTE was found to be lowest for the biodiesel operations compared with the diesel operation. This reduction may be due to their lower volatility, higher viscosity and density, leading to poor mixture formation.

Figure 4 Effect of the variation in brake power on BTE.

4.2 Emission parameters

4.2.1 Smoke opacity

The effect of brake power on smoke opacity for diesel, HnOME and COME in the normal engine operation is shown in Figure 5. It can be observed that there was an increase in smoke opacity with an increase in load. Smoke opacity was found to be higher for the biodiesel operations than for the diesel operation. This increase may be due to their higher viscosity associated with a heavier molecular structure containing fatty acids, lower volatility and higher density. This results in poor atomization of biodiesels, leading to higher smoke emissions. At an 80% load, smoke opacity values were found to be 61 and 70 HSU for the HnOME and COME operations, respectively, compared with 53 HSU for the diesel operation.

Figure 5 Effect of the variation in brake power on smoke opacity.

4.2.2 Hydrocarbon (HC) and carbon monoxide (CO) emissions

The effect of brake power on HC and CO emissions for diesel, HnOME and COME is shown in Figures 6 and 7, respectively. HC emission levels were found to be higher for the biodiesels than for the standard diesel oil. The higher HC and CO emissions in the exhaust of the fuel may be attributed to the polymerization that takes place at the core of the spray and causes the concentration of the spray cone, thereby decreasing the penetration rate. (Bari, Lim, and Yu 2002). Low-volatility polymers affect the atomization process and the mixing of the air and fuel, resulting in a locally rich mixture. This feature increases incomplete combustion, and hence higher CO and HC emission levels were observed for both biodiesels. HC emission levels recorded for HnOME and COME in the normal engine operation were found to be 54 and 63 ppm compared with 29 ppm for diesel at an 80% power output.

Figure 6 Effect of the variation in brake power on HC emissions.

Figure 7 Effect of the variation in brake power on CO emissions.

CO emission levels in the exhaust also showed a similar trend as observed for HC emissions. The CO emission values were 0.14 and 0.18% for the HnOME and COME operations but 0.1% for the diesel operation at an 80% load.

4.2.3 Nitric oxide emissions

The effect of brake power on nitric oxide (NO _x ) emissions is shown in Figure 8 for the normal engine operation. It was observed that NO _x emission levels were found to be higher for the diesel operation than for the biodiesel operations. The heat release rates for biodiesels were found to be lower during the premixed combustion phase, leading to lower peak temperatures. Nitrogen oxide formation strongly depends on the peak temperature, which explains the observed phenomenon. The nitrogen oxide emission values recorded for HnOME and COME in the normal engine operation were found to be 760 and 735 ppm at an 80% power output compared with 790 ppm for diesel.

Figure 8 Effect of the variation in brake power on NO _x emissions.

4.3 Combustion parameters

4.3.1 Ignition delay

The effect of brake power on ignition delay is shown in Figure 9. The ignition delay was calculated based on the static injection timing. HnOME and COME showed longer ignition delays compared with diesel. These longer ignition delays could be attributed to the rate of vaporization of the fuel droplets. This in turn depends on the size of the droplets, velocity and distribution, the pressure and temperature inside the cylinder, and the volatility of the fuel itself. The reasons for this observed trend could be the higher viscosity and lower volatility of the biodiesels, leading to poor atomization and poor mixing of the air during the ignition delay period. The lower viscosity of HnOME results in a slightly reduced ignition delay compared to COME engine operation.

Figure 9 Effect of the variation in brake power on ignition delay.

4.3.2 Combustion duration

Combustion duration, shown in Figure 10, was calculated based on the duration between the start of combustion and 90% cumulative heat release. It was observed that combustion duration increased with an increased power output for all the fuels tested, which was due to the increased quantity of the fuels injected. A higher combustion duration was observed with esters than with diesel, which could be attributed to the lower premixed combustion phase. Combustion duration for HnOME and COME were found to be longer than that for diesel due to its longer diffusion combustion phase. Combustion duration was observed to be shorter for HnOME than for COME, yet longer than that for diesel.

Figure 10 Effect of the variation in brake power on combustion duration.

4.3.3 Cylinder pressure

Figure 11 shows the variation in pressure versus crank angle for diesel, HnOME and COME at optimum injection timings. It was observed that the peak pressure increased as the load increased, and combustion started later for HnOME and COME than for diesel fuel in the normal diesel engine operation. A reduction in cylinder pressure was observed for the HnOME and COME operation. This reduction could be attributed to the incomplete combustion and lower energy content of the respective biodiesels compared with diesel fuel with reduced BTE. The peak cylinder pressure was observed to be higher for HnOME than for COME. The reason could be attributed to its higher premixed combustion phase, as shown in Figure 11.

Figure 11 Effect of the variation in cylinder pressure versus crank angle at an 80% load.

4.3.4 Heat release rate

Figure 12 shows the heat release rate for all the fuels tested. It can be observed that a shorter premixed heat release portion occurs for the biodiesels, despite their increased ignition delay. The heat release rates for both HnOME and COME operations were found to be lower than that for the diesel operation. A reduced heat release rate during the premixed combustion phase and an increased heat release rate during the diffusion combustion phase were observed for both HnOME and COME operations compared with the diesel operation. This leads to an increased exhaust gas temperature.

Figure 12 Effect of the variation in heat release rate with HnOME and COME at an 80% load.

4.4 Comparison of LHR coatings for COME and HnOME

This section provides a comprehensive comparison of the performance of the biodiesels with different coatings used in the diesel engine.

4.4.1 Brake thermal efficiency

Figures 13 shows the effect of brake power on BTE for the biodiesel fuelled engine when coated with the TBC of PSZ and Al₂O₃. The performance of the biodiesels improved because of the reduced heat transfer rate for the coated engine operation compared with the normal engine operation. The positive effect of the increased in-cylinder temperature due to such thermal coatings is the reason for this observed trend (Hanbey and Ozturk 2010). For the biodiesels tested, a higher BTE was found with PSZ-coated engine compared to Al₂O₃-coated one. The reduced heat transfer rate from the PSZ-coated engine compared with the Al₂O₃-coated engine could be the reason for this observed trend. The heat-resisting property of PSZ is comparatively better than that of Al₂O₃. Compared with Al₂O₃, the PSZ-coated engine exhibited an increased BTE by 4.5% and 5% when fuelled with COME and HnOME respectively. The BTE values were found to be 24.85%, 24.0%, 26.7% and 25.6% for the HnOME+LHR (Al₂O₃), COME+LHR (Al₂O₃), HnOME+LHR (PSZ) and COME+LHR (PSZ) operations, respectively, compared with 26.2% for the diesel operation at an 80% load.

Figure 13 Effect of the variation in brake power on BTE.

4.4.2 Smoke opacity

The effect of brake power on smoke opacity for both the biodiesels provided with the TBC of PSZ and Al₂O₃ is shown in Figure 14. The coating of the ceramic elements on the combustion chamber increases in-cylinder soot oxidation due to a higher surface temperature, resulting in improved combustion efficiency (Hanbey and Ozturk 2010). A significant decrease in smoke density for the PSZ-coated engine was observed compared with the Al₂O₃-coated engine. Better combustion with a reduced heat transfer rate from the PSZ-coated engine compared with the Al₂O₃-coated one could be the reason for this observed trend. PSZ being a ceramic material has a very low thermal conductivity, good strength and low thermal expansion coefficient, and it can withstand a much higher temperature than Al₂O₃. The smoke emission levels were found to be 63, 67, 58 and 61 HSU for the HnOME+LHR (Al₂O₃), COME+LHR (Al₂O₃), HnOME+LHR (PSZ) and COME+LHR (PSZ) operations, respectively, compared with 53 HSU for the diesel operation at an 80% load.

Figure 14 Effect of the variation in brake power on smoke opacity.

4.4.3 HC and CO emissions

Figures 15 and 16 show the effect of the variations in brake power on HC and CO emissions for the biodiesels with the TBC of PSZ and Al₂O₃. For the biodiesel operations, the HC and CO emission levels were found to be lower in the thermal barrier-coated engine than in the uncoated or normal engine. This decrease in HC and CO emission levels in the coated engine may be attributed to the increased post-combustion temperature due to the decreased heat loss to both cooling media, cylinder and engine parts. This may lead to the addition of more unburned HC to the combustion. The reduction in both HC and CO emission levels is due to the decreased quenching distance and the increased lean flammability limit. The higher temperatures prevailing in both gases and at the combustion chamber walls of the thermal barrier-coated engine assist in permitting the oxidation reactions to proceed closer to completion (Ahmaniemi et al. 2004). Of the two coated engines, the lowest HC and CO emission levels were found in the PSZ-coated engine. The higher surface temperature prevailing inside the PSZ-coated combustion chamber improves combustion with higher heat utilization using the biodiesel operation. The HC emission levels were found to be 46, 52, 39 and 41 ppm for the HnOME+LHR (Al₂O₃), COME+LHR (Al₂O₃), HnOME+LHR (PSZ) and COME+LHR (PSZ) operations, respectively, compared with 36 ppm for the diesel operation at an 80% load. Similarly, the CO emission levels were found to be 0.265%, 0.29%, 0.24% and 0.26% for the HnOME+LHR (Al₂O₃), COME+LHR (Al₂O₃), HnOME+LHR (PSZ) and COME+LHR (PSZ) operations, respectively, compared with 0.18% for the diesel operation at an 80% load.

Figure 15 Effect of the variation in brake power on HC emissions.

Figure 16 Effect of the variation in brake power on CO emissions.

4.4.4 Nitric oxide emissions

The effect of brake power on NO _x emissions for both the biodiesels provided with the TBC of PSZ and Al₂O₃ is shown in Figure 17. Lower NO _x emission levels were observed in the normal engine compared with the thermal barrier-coated engine. The increased post-combustion temperature causes an increase in NO _x emission levels compared with the uncoated engine. Factors facilitating and accelerating the reaction between oxygen and nitrogen increases the formation of NO _x . The NO _x emission levels were found to be 1140, 1080, 1050 and 890 ppm for the HnOME+LHR (PSZ), COME+LHR (PSZ), HnOME+LHR (Al₂O₃) and COME+LHR (Al₂O₃) operations, respectively, compared with 1310 ppm for the diesel operation at an 80% load.

Figure 17 Effect of the variation in brake power on NO _x emissions.

4.4.5 Ignition delay

The effect of brake power on ignition delay is shown in Figure 18. The ignition delay was calculated based on the static injection timing. HnOME and COME showed longer ignition delays compared with diesel. The reasons for this observed trend are the higher viscosity and lower volatility of the biodiesels, leading to poor atomization and poor mixing of the air during the ignition delay period (Suresh, Kamath, and Banapurmath 2013). However, the increased gas temperature in the thermal barrier-coated engine improved combustion with a shortened ignition delay and positively affected both chemical and physical reactions. From Figure 18, it can be observed that PSZ caused a lower ignition delay than did Al₂O₃.

Figure 18 Effect of the variation in brake power on ignition delay.

4.4.6 Combustion duration

Combustion duration shown in Figure 19 was calculated based on the duration between the start of combustion and 90% cumulative heat release. It was observed that combustion duration increased with an increase in the power output for all the fuels tested. This increase is due to the increase in the quantity of the fuels injected. Combustion duration for HnOME and COME was found to be longer than that for diesel due to its longer diffusion combustion phase (Suresh, Kamath, and Banapurmath 2013). However, it could be lowered with increased cylinder temperature by incorporating the LHR facility. Combustion duration for HnOME and COME was observed to be shortened with the PSZ coating, yet longer than that for diesel.

Figure 19 Effect of the variation in brake power on combustion duration.

4.4.7 Cylinder pressure

Figure 20 shows the variation in pressure versus crank angle for the HnOME and COME oils. Combustion started later for both the biodiesels compared to diesel in both versions LHR and standard engine modes of operation. The PSZ coating exhibited a slightly higher peak pressure compared to Al₂O₃.

Figure 20 Effect of the variation in cylinder pressure versus crank angle at an 80% load.

4.4.8 Heat release rate

Figure 21 compares the heat release rates at an 80% load. The premixed burning phase associated with a high heat release rate was found to be significant for the standard diesel operation, and responsible for the higher peak pressure and higher rates of pressure rise (Suresh, Kamath, and Banapurmath 2013). This trend could be attributed to the higher thermal efficiency observed for diesel fuel operation. The heat release rate depends on the premixed fuel and air mixture, energy content and flame velocity of the fuels used. The diffusion combustion and burn rate is controlled by the mixing of the fuel and air. It can be observed that combustion started earlier for the coated engine at all engine loads for all the tested fuels. At higher engine loads, the heat release rate for the thermal barrier-coated engine was found to be higher. The crank angle at which the maximum heat release rate occurred was in advance for the thermal barrier-coated engine compared with the normal engine. The heat release rate was lower for the PSZ-coated engine than for the Al₂O₃-coated engine. This decrease could be attributed to the higher ignition delay for the Al₂O₃ coating compared with the PSZ coating. This may be due to the fact that more fuel is accumulated in the combustion chamber to release higher heat during the premixed combustion phase (Mohamed Musthafa, Sivapirakasam, and Udayakum 2011).

Figure 21 Effect of the variation in heat release rate with HnOME and COME at an 80% load.

5. Conclusions

The following conclusions are made from the present study:

• The study on the performance of diesel, HnOME and COME in the CI engine indicates that no major modifications are required in the existing diesel engine. The use of non-edible oils avoids the conflict between food and energy security.

• BTE for the HnOME and COME operations was slightly lower than that for the diesel fuel operation. At the operating conditions, the BTE of the engine decreased by 4.9% and 9.5% for the HnOME and COME operations compared with the diesel fuel operation.

• The smoke opacity, HC and CO emission levels were slightly higher for the HnOME and COME operations than for the diesel fuel operation. Smoke opacity was increased by 15.8% and 32.5%, HC emission levels increased by 41.1% and 51% and CO emission levels increased by 35.6% and 44.2% for the HnOME and COME operations compared with the diesel fuel operation.

• The NO _x emission levels for the biodiesels were found to be lower than that for diesel fuel. The levels were decreased by 4.2% and 7.8% for the HnOME and COME operations compared with the diesel fuel operation.

• The LHR operation with HnOME and COME produced an improvement in BTE when compared with the standard engine operation. However, this improvement did not match with the standard diesel engine operation. The BTE values were increased by 4% and 3.2%, respectively, compared with the normal engine operation for the respective biodiesels.

• Higher smoke, HC and CO emission levels were observed for the HnOME and COME operations than for the standard diesel operation. The emission levels were reduced in the thermal barrier-coated engine or the LHR engine.

• The LHR operation with HnOME and COME appeared to produce slightly higher NO _x levels than that for the normal engine operation with the biodiesels, whereas the standard diesel operation exhibited maximum NO _x emission levels.

• The heat release rate was better for the HnOME and COME operation with the LHR facility compared with the normal engine operation, resulting in improved BTE.

• Based on the engine test, it could be concluded that esters of vegetable oils (HnOME and COME) can replace diesel fuel for running the existing diesel engine without any major engine modification, and its performance with PSZ coating is better than that with Al₂O₃ coating.

Notes

^1. Email: [email protected]

^2. Email: [email protected]