Comparative Studies on Performance Parameters of Direct Injection Diesel Engine with Ceramic Coated Low Heat Rejection Combustion Chamber with Rice Brawn Oil Based Biodiesel

Comparative Studies on Performance Parameters of Direct Injection Diesel Engine with Ceramic Coated Low Heat Rejection Combustion Chamber with Rice Brawn Oil Based Biodiesel

M. V. S. Murali Krishna1, N. Durga Prasada Rao2, B. Anjenaya Prasad3 and P. V. K. Murthy4

1Mechanical Engineering Department, Chaitanya Bharathi Institute of Technology,Gandipet, Hyderabad-500 075,

Andhra Pradesh, India

2Production Department, Hindustan Aeronautics Limited, Bangalore- 560017,

3Mechanical Engineering Department, J.N.T. U. College of Engineering, Hyderabad- 500 085,

4 Jaya Prakash Narayan Educational Society Group of Institutions, Mahabubnagar-509001, Andhra Pradesh, India.

Abstract

Investigations were carried out to evaluate the performance of diesel engine with low heat rejection (LHR) combustion chamber consisting of ceramic coated cylinder head ( partially stabilized zirconium of thickness 500 microns was coated on inside portion of cylinder head) with superni insert with different operating conditions (normal temperature and preheated temperature) of rice brawn oil based biodiesel (ERBO) with varied injection timing and injector opening pressure. Performance parameters [brake thermal efficiency, exhaust gas temperature, sound levels, coolant load and volumetric efficiency] were determined at various values of brake mean effective pressure (BMEP) of the engine and compared with conventional engine with biodiesel operation at similar operating conditions. Biodiesel showed compatible performance with conventional engine (CE), while LHR combustion chamber improved the performance in comparison with pure diesel operation at similar operating conditions. The optimum injection timing was found to be 31obTDC with CE while it was 30obTDC for ceramic coated LHR combustion chamber with biodiesel operation. Relatively, with LHR combustion chamber with biodiesel operation, peak brake thermal efficiency increased by 3%, at full load operation- brake specific energy consumption was compatible, exhaust gas temperature decreased by 50oC, coolant load decreased by 5%, sound levels decreased by 9% and volumetric efficiency was compatible in comparison with pure diesel operation at similar operating conditions.

Key Words: Need for Alternate Fuels, Vegetable Oil, Biodiesel, LHR combustion chamber, Performance.

1. Introduction

   This section deals with need and necessity of alternative fuels and various alternative fuels. Investigations carried out by various researchers on crude vegetable oils and biodiesel at normal temperature and preheated temperature in compression ignition engine were mentioned. Conclusions from their investigations were given. Objectives of the investigations were given at the end of the section

   The resources of petroleum [1] as fuel are dwindling day by day and increasing demand of fuels, as well as increasingly stringent regulations, pose a challenge to science and technology. With the commercialization of bio-energy, it has provided an effective way to fight against the problem of petroleum scarce and the influence on environment.

   Alcohols have good volatility and low C/H ratio. However, they have low cetane number. Hence engine modification is necessary for use them as fuel in diesel engines. That too, most of the alcohol produced is diverted for Petro-chemical industries in India.

   Vegetable oils which are renewable in nature have properties compatible to diesel fuel. Rudolph Diesel, the inventor of the diesel engine that bears his name, experimented [2] with fuels ranging from powdered coal to peanut oil. Several researchers [3- 6] experimented the use of vegetable oils as fuel on conventional engines (CE) and reported that the performance was poor, citing the problems of high viscosity, low volatility and their polyunsaturated character. Not only that, the common problems of crude vegetable oils in diesel engines are formation of carbon deposits, oil ring sticking, thickening and gelling of lubricating oil as a result of contamination by the vegetable oils.

   Experiments were conducted [7-10] on preheated vegetable oils [temperature at which viscosity of the vegetable oils were matched to that of diesel

   fuel] and it was reported that preheated vegetable oils improved the performance marginally. The problems of crude vegetable oils can be solved, if these oils are chemically modified to bio-diesel.

   The U.S. Department of Energy has stated [11] that, Raw or refined vegetable oil, that have not been processed into biodiesel, are not biodiesel and should be avoided. The use of raw, unprocessed vegetable oils or animal fats in diesel engines regardless of blend level can have significant adverse effects and should not be used as fuel in diesel engines. Raw or refined vegetable oil, or recycled greases have significantly different and widely varying properties that are not acceptable for use in modern diesel engines. For example, the higher viscosity and chemical composition of unprocessed oils and fats have been shown to cause problems in a number of areas: (i) piston ring sticking; (ii) injector and combustion chamber deposits; (iii) fuel system deposits; (iv) reduced power; (v) reduced fuel economy and(vi) increased exhaust emissions vii) dilution of lubricating oil,

   viii) reduced engine life, ix) increased maintenance cost, xi) stress on fuel injection system. The above mentioned problems are reduced if crude vegetable oils are converted [11] into biodiesel, which have low molecular weight, low dense and low viscosity when compared with crude vegetable oils. Investigations were carried out [12-16] with biodiesel with CE. It was reported from their investigations, that biodiesel operation improved the performance, reduced smoke emissions and increased NOx emissions. The drawbacks associated with biodiesel and crude vegetable oils for use in diesel engines call for LHR hot combustion chamber.

   The concept of LHR combustion chamber is to reduce coolant losses by providing thermal resistance in the path of heat flow to the coolant, there by gaining thermal efficiency. Several methods adopted for achieving LHR to the coolant are i) ceramic coated combustion chambers and ii) air gap insulated combustion chambers. Air gap is created in the piston and other components with low-thermal conductivity materials like superni, cast iron and mild steel etc for air gap insulated combustion chambers.

   LHR combustion chambers were classified as low degree, medium grade and high grade LHR combustion chambers depending on degree of insulations.

   Investigations were carried out by various researchers [17-19] on engines with low degree LHR combustion chambers-(ceramic coated engines) with pure diesel operation. It was reported from their investigations that brake specific fuel consumption (BSFC) improved in the range 5-9% and pollution levels decreased with ceramic coated combustion chamber. Studies were also made [20-

   22] on ceramic coated LHR combustion chamber with biodiesel operation. It was reported that performance improved with biodiesel operation.

   Sound levels determine the phenomena of combustion in engine whether the performance was improving or deteriorating. Studies were made [23- 25] on sound levels with medium grade LHR combustion chamber with vegetable oils. It was reported from the studies, that performance deteriorated with vegetable oil operation on conventional engine leading to produce high sound levels and improved with LHR combustion chamber causing low sound levels.

   Rice bran oil is an underutilized non-edible vegetable oil, which is available in large quantties in rice cultivating countries, and very little research has been done to utilize this oil as a replacement for mineral Diesel. Little literature was available on comparative studies of rice bran oil based biodiesel with ceramic coated combustion chamber and engine with conventional combustion chamber.

   Hence it was attempted here to evaluate the performance of the engine with rice bran oil based biodiesel at different operating conditions with varied injection timing and injector opening pressure. The standard fuel was taken as diesel for reference

2. Methodology

   This part deals with preparation of biodiesel, properties of biodiesel along with diesel fuels, fabrication of air gap insulated piston and air gap insulated liner, brief description of experimental set-up, specification of experimental engine, operating conditions and definitions of used values. Due to very high free fatty acid, rice bran oil was converted into methyl ester by the two stage process [26]. In the first stage rice bran oil was reacted with CH3OH in presence of an acid catalyst (H2SO4) to convert free fatty acid into fatty ester. A specified amount 1000g of rice bran oil was taken in a round bottom flask and heated up to 60- 65°C. In a separate flasks CH3OH (950 g) and H2SO4 (22 g) were taken and properly mixed and then stirred for 4 h and maintained at 60°C.It was allowed to cool overnight without stirring. When acid number of the mixture reaches to less than 1, the second stage was started. During this stage, a mixture 1000g obtained from the first stage was taken in around bottom flask and heated up to 60°C. Methanol (200ml) and KOH 4.5g were properly mixed in other flask and then introduced into the round bottom flask containing the mixture from first stage. The mixture stirred vigorously for 2h and then allowed to cool overnight. Glycerol was separated by adding warm water at 60°C to the mixture. Glycerol and soap formed during the process settled down the bottom. Top layer

   containing rice bran oil methyl ester 91% was removed with the help of a separating funnel and wasted

   two times with water and dried.

   The physic-chemical properties of the biodiesel in comparison to ASTM biodiesel standards are presented in Table-1.

   Table 1. Properties of Test Fuels

   Property	Units	Diesel	Biodiesel (ERBO)	ASTM D 6751- 02
   Carbon chain	—	C8-C28	C16-C24	C12-C22
   Cetane Number		55	52	48-70
   Density	gm/cc	0.84	0.86	0.87-0.89
   Bulk modulus @ 20Mpa	Mpa	1475	1800	NA
   Kinematic viscosity @ 40oC	cSt	2.25	3.5	1.9-6.0
   Sulfur	%	0.25	0.0	0.05
   Oxygen	%	0.3	11	11
   Air fuel ratio ( stochiometric)	—	14.86	13.8	13.8
   Lower calorific value	kJ/kg	42 000	38500	37 518
   Flash point (Open cup)	oC	66	174	130
   Molecular weight	—	226	261	292
   Preheated temperature	oC	—	65	—
   Colour	—	Light yellow	Yellowish orange	—

   Schematic diagram of experimental setup used for the investigations on compression ignition diesel engine and LHR combustion chamber with biodiesel (ERBO) is shown in Figure 1.

   The test fuels used in the experimentation were pure diesel and rice bran oil based biodiesel. The schematic diagram of the experimental setup with test fuels is shown in Figure 2. The specifications of the experimental engine are shown in Table-2. The combustion chamber consisted of a direct injection type with no special arrangement for swirling motion of air. The engine was connected to an electric dynamometer for measuring its brake power. Burette method was used for finding fuel consumption of the engine. Air-consumption of the engine was measured by an air-box method (Air box was provided with an orifice flow meter and U-tube water manometer). The naturally aspirated engine was provided with water-cooling system in

   which inlet temperature of water was maintained at 80oC by adjusting the water flow rate. Engine oil was provided with a pressure feed system. No temperature control was incorporated, for measuring the lube oil temperature. Copper shims of suitable size were provided in between the pump body and the engine frame, to vary the injection timing and its effect on the performance of the engine was studied, along with the change of injector opening pressure from 190 bar to 270 bar (in steps of 40 bar) using nozzle testing device. The maximum injector opening pressure was restricted to 270 bar due to practical difficulties involved. Exhaust gas temperature was measured with thermocouples made of iron and iron-constantan.

   Partially stabilized zirconium of thickness 0.5 mm was coated on inside portion of cylinder head by plasma spray technique.

   Table 2. Specifications of the Test Engine

   Description	Specification
   Engine make and model	Kirloskar ( India) AV1
   Maximum power output at a speed of 1500 rpm	3.68 kW
   Number of cylinders ×cylinder position× stroke	One × Vertical position × four-stroke
   Bore × stroke	80 mm × 110 mm
   Method of cooling	Water cooled
   Rated speed ( constant)	1500 rpm
   Fuel injection system	In-line and direct injection
   Compression ratio	16:1
   BMEP @ 1500 rpm	5.31 bar
   Manufacturers recommended injection timing and pressure	27obTDC × 190 bar
   Dynamometer	Electrical dynamometer
   Number of holes of injector and size	Three × 0.25 mm
   Type of combustion chamber	Direct injection type
   Fuel injection nozzle	Make: MICO-BOSCH No- 0431-202-120/HB
   Fuel injection pump	Make: BOSCH: NO- 8085587/1

   1. Engine, 2.Electical Dynamometer, 3.Load Box, 4.Orifice flow meter, 5.U-tube water manometer, 6.Air box, 7.Fuel tank, 8, Pre- heater, 9.Burette, 10. Exhaust gas temperature indicator, 11.Outlet jacket water temperature indicator, 12. Outlet-jacket water flow meter,

      Figure 1. Schematic Diagram of Experimental

      Set-up

      Various test fuels used in experimentation were pure diesel and rice bran oil based biodiesel. Different operating conditions of the biodiesel were normal temperature and preheated temperature. Different injector opening injector opening pressures attempted in this experimentation were 190 bar, 230 bar and 270 bar. Various injection timings attempted in the investigations were 27- 34obTDC.

      Definitions of used values:

      Brake thermal efficienc (BTE); It is the ratio of brake power of the engine to the energy supplied to the engine. Brake power was measured with dynamometer. Energy supplied to the engine is the product of rate of fuel consumed (mf)and calorific value (cv)of the fuel. Higher the efficiency better the performance of the engine is.

      Brake specific energy consumption (BSEC): It is measured at full load operation of the engine. Lower the value, the better the performance of the engine. It is defined as energy consumed by the engine in producing 1 kW brake power. When different fuels having different properties are tested in engine, brake specific fuel consumption is not the criteria to evaluate the performance of the engine. Peak BTE and BSEC at full load are important parameters to be considered to evaluate the performance of the engine.

      Coolant load: Product of mass flow rate of coolant, specific heat of coolant, rise of temperature of the coolant between inlet conditions and outlet conditions.

      Volumetric efficiency: It is the ratio of the volume of air drawn into a cylinder to the piston displacement.

      Recommended injection timing: It is the injection timing of the engine with maximum efficiency of the engine with minimum pollution levels.

      Calculation of actual discharge of air: By means of water tube manometer and an orifice flow meter, head of air (ha) can be calculated. Velocity of air (Va) can be calculated using the formula

      ; Actual discharge of air

      = , where a= area of an orifice flow

      meter, cd = Coefficient of discharge.

      Optimum injection timing: It is injection timing at which maximum thermal efficiency was obtained at all loads and beyond this injection timing, efficiency of the engine decreased.

3. Results and Discussion

This section is divided into determination of performance parameters with biodiesel operation on engine with conventional combustion chamber and ceramic coated LHR combustion chamber.

Data of pure diesel was taken from reference [27]. The optimum injection timing with conventional engine was 31obTDC, while with LHR combustion chamber it was 30obTDC.

3.1 Performance Parameters

Figure 2 indicates that BTE increased up to 80% of the full load operation (BMEP=4.2 bar) due to conversion of increase of fuel efficiency and beyond that load it decreased due to decrease of air fuel ratios [27] as oxygen was completely used up with both test fuels. Curves from Figure 3 indicate

that CE with bio-diesel showed the compatible performance for entire load range when compared with the pure diesel operation on CE at recommended injection timing. Although carbon accumulations on the nozzle tip might play a partial role for the general trends observed, the difference of viscosity between the diesel and bio-diesel provided a possible explanation for the compatible performance of CE with bio-diesel operation.

Figure 3. Variation of brake thermal efficiency (BTE) with brake mean effective pressure (BMEP) in conventional engine (CE) at various injection timings with biodiesel (ERBO) operation at an injector opening pressure of 190 bar.

BTE increased with the advancing of the injection timing in the CE with the bio-diesel at all loads, when compared with CE at the recommended injection timing and pressure. This was due to initiation of combustion at earlier period and efficient combustion with increase of air entrainment [26] in fuel spray giving higher BTE. BTE increased at all loads when the injection timing was advanced to 31obTDC in CE at the normal temperature of bio-diesel.

Similar trends were observed with preheated biodiesel also. Preheating of the biodiesel reduced the viscosity, which improved the spray characteristics of the oil.

From Figure 3, it is observed that LHR combustion chamber with biodiesel showed the improved performance for the entire load range compared with CE with pure diesel operation. This was because of efficient combustion of biodiesel in the hot environment provided by ceramic coated LHR combustion chamber. The optimum injection timing was found to be 30obTDC with ceramic coated LHR combustion chamber with normal bio- diesel and preheated biodiesel operations. Since LHR combustion chamber reduced ignition delay and combustion duration and hence the optimum

injection timing was obtained earlier with ceramic coated LHR combustion chamber when compared with CE with the biodiesel operation.

Figure 3. Variation of brake thermal efficiency (BTE) with brake mean effective pressure (BMEP) in ceramic coated LHR combustion chamber at various injection timings with biodiesel (ERBO) operation an injector opening pressure of 190 bar.

Injector opening pressure was varied from 190 bars to 270 bar to improve the spray characteristics and atomization of the vegetable oils and injection timing was advanced from 27 to 34obTDC for CE and LHR engine. The improvement in BTE at higher injector opening pressure was due to improved fuel spray characteristics. The optimum injection timing was 31obTDC at 190 bar, 30obTDC at 230 bar and 29obTDC at 270 bar for CE. The optimum injection timing for LHR combustion chamber was 30obTDC irrespective of injector opening pressure.

Part load variations were very small and minute for the performance parameters and exhaust emissions. The effect of varied injection timing on the performance was discussed with the help of bar charts while the effect of injector opening pressure and preheating was discussed with the help of Tables.

it was noticed (Figure.5) that peak brake thermal efficiency(BTE)with LHR combustion chamber engine with pure diesel operation was lower in comparison with conventional engine at recommended (4%) and optimized injection timings (3%).

LHR combustion chamber [27] with pure diesel operation deteriorated the performance in comparison with conventional engine. As the

combustion chamber was insulated to greater extent, it was expected that high combustion temperatures would be prevalent in LHR combustion chamber. It tends to decrease the ignition delay thereby reducing pre-mixed combustion as a result of which, less time was available for proper mixing of air and fuel in the combustion chamber leading to incomplete combustion, with which peak BTE decreased. More over at this load, friction and increased diffusion combustion resulted from reduced ignition delay.

Peak BTE with LHR combustion chamber with biodiesel operation was higher in comparison with conventional engine at recommended (8%) and optimized injection timings (3%).

This was due to higher degree of insulation provided in the piston, liner (with the provision of air gap with superni-90 inserts) and cylinder head reduced the heat rejection leading to improve the thermal efficiency. This was also because of improved evaporation rate of the biodiesel. High cylinder temperatures [26] helped in better evaporation and faster combustion of the fuel injected into the combustion chamber. Reduction of ignition delay [27] of the vegetable oil in the hot environment of the LHR engine improved heat release rates and efficient energy utilization.

From Table 3, it could be noticed that improvement in the peak BTE was observed with the increase of injector opening pressure and with advancing of the injection timing in both versions of the combustion chamber. This was due to improved spraying characteristics and efficient combustion as biodiesel has high duration of combustion and hence advancing of injection timing helped efficient energy release from the fuel leading to produce higher BTE.

The performance improved further with the preheated biodiesel when compared with normal biodiesel.

Preheating of the biodiesel reduced the viscosity, which improved the spray characteristics of the oil causing efficient combustion thus improving brake thermal efficiency. The cumulative heat release was more for preheated biodiesel [29] than that of biodiesel and this indicated that there was a significant increase of combustion in diffusion mode [27]. This increase in heat release [28] was mainly due to better mixing and evaporation of preheated biodiesel, which leads to complete burning.

LHR combustion chamber with biodiesel operation gave higher BTE than CE, while CE gave higher BTE than ceramic coated LHR combustion chamber with diesel operation.

Figure. 5. Bar charts showing the variation of Peak brake thermal efficiency with test fuels at recommended and optimized injection timings at an injector opening pressure of 190 bar in different versions of combustion chambers.

Table 3. Data of peak BTE

DF-Diesel Fuel, ERBO- Biodiesel, NT- Normal or Room Temperature, PT- Preheat Temperature

Generally brake specific fuel consumption, is not used to compare the two different fuels, because their calorific value, density, chemical and physical parameters are different. Performance parameter, BSEC, is used to compare two different fuels by normalizing brake specific energy consumption, in terms of the amount of energy released with the given amount of fuel.

From Table 4, it is evident that brake specific energy consumption (BSEC) at full load decreased with the increase of injector opening pressure and with the advancing of the injection timing at different operating conditions of the biodiesel. This was because of improved spray characteristics with increase of injector opening pressure. This was also due to initiation of combustion at early period with advanced injection timing.

From Figure.6, it was evident that brake specific energy consumption with engine with ceramic coated LHR combustion chamber with pure diesel operation was higher in comparison with conventional engine at recommended (10%) and optimized injection timings (4%).

Figure. 6. Bar charts showing the variation of brake specific energy consumption (BSEC) at full load operation with test fuels at recommended and optimized injection timings at an injector opening pressure of 190 bar in different versions of combustion chambers.

Table 4. Data of BSEC at full load operation

DF-Diesel Fuel, ERBO- Biodiesel, NT- Normal or Room Temperature, PT- Preheat Temperature

This was due to reduction of ignition delay with pure diesel operation with LHR combustion chamber as hot combustion chamber was maintained by it.

BSEC was lower with LHR combustion chamber with biodiesel operation in comparison with conventional engine with biodiesel operation at recommended injection timing (4%) and optimum injection timing (2%).

BSEC was higher with conventional engine due to due to higher viscosity, poor volatility and reduction in heating value of biodiesel lead to their poor atomization and combustion characteristics. The viscosity effect, in turn atomization was more predominant than the oxygen availability [28] in the blend leads to lower volatile characteristics and affects combustion process. BSEC was improved with medium grade LHR combustion chamber with lower substitution of energy in terms of mass flow rate.

BSEC decreased with advanced injection timing with test fuels. This was due to initiation of combustion and substitution of lower energy as seen From the Figure.6i.

BSEC of biodiesel is almost the same as that of neat diesel fuel as shown in Figure.6. Even though viscosity of biodiesel is slightly higher than that of neat diesel, inherent oxygen of the fuel molecules improves the combustion characteristics. This is an indication of relatively more complete combustion [28].

BSEC decreased with the preheated biodiesel at full load operation when compared with normal biodiesel. Preheating of the biodiesel reduced the viscosity, which improved the spray characteristics of the oil.

From Figure.7, it was observed that exhaust gas temperature (EGT) with LHR combustion chamber with pure diesel operation was higher in comparison with conventional engine at recommended (12%) and optimized injection timings (15%).

This was due to reduction of ignition delay with pure diesel operation with engine with LHR

combustion chamber. This indicated that heat rejection was restricted through the piston, liner and cylinder head, thus maintaining the hot combustion chamber as result of which the exhaust gas temperature increased.

EGT with LHR combustion chamber with biodiesel operation was marginally lower in comparison with conventional engine at recommended (9%)and optimized injection timings (5%). This was due to reduction of ignition delay in the hot environment with the provision of the insulation in the LHR engine, which caused the gases expand in the cylinder giving higher work output and lower heat rejection.

EGT decreased with advanced injection timing with test fuels as seen from the Figure. This was because, when the injection timing was advanced, the work transfer from the piston to the gases in the cylinder at the end of the compression stroke was too large, leading to reduce in the value of EGT. Though the calorific value (or heat of combustion) of fossil diesel is more than that of biodiesel ; the density of the biodiesel was higher therefore greater amount of heat was released in the combustion chamber leading to higher exhaust gas temperature with conventional engine, which confirmed that performance was compatible with conventional engine with biodiesel operation in comparison with pure diesel operation. Similar findings were obtained by other studies [27].

From the Table.5, it is noticed that the exhaust gas temperatures of preheated biodiesel were higher than that of normal biodiesel, which indicates the increase of diffused combustion [28] due to high rate of evaporation and improved mixing between methyl ester and air. Therefore, as the fuel temperature increased, the ignition delay decreased and the main combustion phase (that is, diffusion controlled combustion) increased [28] , which in turn raised the temperature of exhaust gases. The value of exhaust gas temperature decreased with increase in injector opening pressure with test fuels as it is evident from the Table.5. This was due to

improved spray characteristics of the fuel with increase of injector opening pressure.

Exhaust gas temperature was lower with diesel operation with conventional engine when compared with biodiesel operation, while EGT was lower with engine with ceramic coated LHR combustion chamber with biodiesel operation in comparison with diesel operation. Hence conventional engine was more suitable for diesel operation, while engine with LHR combustion chamber was suitable for biodiesel operation.

Figure. 7. Bar charts showing the variation of exhaust gas temperatures (EGT) at full load with test fuels at recommended and optimized injection timings at an injector opening pressure of 190 bar in different versions of combustion chambers.

Table 5. Data of exhaust gas temperature (EGT) at full load operation

Figure 8 indicates that coolant load with engine with ceramic coated LHR combustion chamber with pure diesel

operation was lower (5% and 14%) at recommended and optimized injection timings respectively in comparison with conventional engine. This was due insulation provided with medium grade LHR combustion chamber.

Coolant load with LHR engine with biodiesel operation was lower (14% and 30%) at recommended and optimized injection timings respectively in comparison with conventional engine. This was due insulation provided with engine with ceramic coated LHR combustion chamber.

In case of conventional engine, un-burnt fuel concentration reduced with effective utilization of energy, released from the combustion, coolant load with test fuels increased marginally at full load operation, due to un-burnt fuel concentration reduced with effective utilization of energy,

released from the combustion, with increase of gas temperatures, when the injection timing was advanced to the optimum value. However, the improvement in the performance of the conventional engine was due to heat addition at higher temperatures and rejection at lower temperatures, while the improvement in the efficiency of the engine with LHR combustion chamber was due to recovery from coolant load at their respective optimum injection timings with test fuels. Rama Mohan [29] noticed the similar trend at optimum injection timing with his LHR engine.

From Table.6, it is seen that coolant load increased marginally in the conventional engine while it decreased in the LHR combustion chamber with increasing of the injector opening pressure with test fuels. This was due to the fact with increase of injector opening pressure with conventional engine,

increased nominal fuel spray velocity resulting in better fuel-air mixing with which gas temperatures increased. The reduction of coolant load in the engine with medium grade LHR combustion chamber was not only due to the provision of the insulation but also it was due to better fuel spray characteristics and increase of air-fuel ratios causing decrease of gas temperatures and hence the coolant load.

Figure. 8. Bar charts showing the variation of coolant load at full load operation with test fuels at recommended and optimized injection timings at an injector opening pressure of 190 bar in different versions of combustion chambers.

Table 6. Data of Coolant Load at full load operation

Coolant load decreased marginally with preheating of biodiesel. This was due to improved air fuel ratios [26] with improved spray characteristics.

Figure 9 denotes that sound levels were higher (12% and 23%) with LHR combustion chamber with pure diesel operation at recommended and optimized injection timings respectively in comparison with conventional engine. This showed that performance deteriorated with engine with ceramic coated LHR combustion chamber with pure diesel operation. This was due to reduction of ignition delay.

Sound levels were lower (30% and 25%) with engine with ceramic coated LHR combustion chamber with biodiesel operation at recommended and optimized injection timings respectively in comparison with conventional engine. This showed that performance improved with engine with ceramic coated LHR combustion chamber with biodiesel operation.

Figure. 9. Bar charts showing the variation of sound levels at full load operation with test fuels at recommended and optimized injection timings at an injector opening pressure of 190 bar in different versions of combustion chambers

With advanced injection timings, air fuel ratios improved with early initiation of combustion hence sound levels got reduced with both versions of the engine with test fuels.

Table 7 denotes that the Sound levels decreased with increase of injector opening pressure with the test fuels. This was due to improved spray characteristic of the fuel, with which there was no

impingement of the fuel on the walls of the combustion chamber leading to produce efficient combustion.

Sound intensities were lower at preheated condition of preheated biodiesel when compared with their normal condition. This was due to improved spray characteristics, decrease of density and viscosity of the fuel.

Table 7. Data of sound intensity at full load operation

Volumetric efficiency depends on density of the charge which intern depends on temperature of combustion chamber wall. Figure 10 denotes that volumetric efficiency were lower (8% and 11%) with LHR combustion chamber with pure diesel operation at recommended and optimized injection timings respectively in comparison with conventional engine.

Volumetric efficiencies were lower (5% and 8%) with LHR combustion chamber with biodiesel operation at recommended and optimized injection timings respectively in comparison with conventional engine.

Volumetric efficiency in the LHR combustion chamber decreased at full load operation when compared to the conventional engine at recommended and optimized injection timing with test fuels. This was due increase of temperature of incoming charge in the hot environment created with the provision of insulation, causing reduction in the density and hence the quantity of air. However, this variation in volumetric efficiency is very small between these two versions of the engine, as volumetric efficiency mainly depends

Figure. 10. Bar charts showing the variation of volumetric efficiency at full load operation with test fuels at recommended and optimized injection timings at an injector opening pressure of 190 bar in different versions of combustion chambers.

Volumetric efficiency was higher with pure diesel operation at recommended and optimized injection timing with conventional engine in comparison with biodiesel operation. This was due to increase of combustion chamber wall temperatures with biodiesel operation due to accumulation of un- burnt fuel concentration. This was also because of increase of combustion chamber wall temperature as exhaust gas temperatures increased with biodiesel operation in comparison with pure diesel operation.

Volumetric efficiency increased marginally with both versions of the combustion chambers with test fuels with advanced injection timing. This was due to decrease of combustion chamber wall temperatures with improved air fuel ratios [29].

From Table-8, it is evident that volumetric efficiency increased with increase of injector opening pressure with test fuels. This was due to improved fuel spray characteristics and evaporation at higher injection pressures leading to marginal increase of volumetric efficiency. This was also

because of decrease of exhaust gas temperatures and hence combustion chamber wall temperatures. This was also due to the reduction of residual fraction of the fuel, with the increase of injector opening pressure.

Preheating of the biodiesel marginally decreased volumetric efficiency, when compared with the normal temperature of biodiesel, because of reduction of bulk modulus, density of the fuel and increase of exhaust gas temperatures.

Table 8. Data of volumetric efficiency at full load operation

4 Conclusions

1. Peak BTE with engine with ceramic coated LHR combustion chamber with biodiesel operation was higher in comparison with conventional engine at recommended (3%) and compatible at optimized injection timing.

2. BSEC was compatible at recommended injection timing and optimum injection timing.

3. EGT with LHR combustion chamber with biodiesel operation was marginally lower in comparison with conventional engine at recommended (15%)and optimized injection timings (13%).

4. Coolant load with LHR engine with biodiesel operation was lower (9% and 26%) at recommended and optimized injection timings respectively in comparison with conventional engine.

5. Sound levels were lower (20% and 38%) with LHR combustion chamber with biodiesel operation at recommended and optimized injection timings respectively in comparison with conventional engine.

6. Volumetric efficiencies were lower (4% and 7%) with LHR combustion chamber with biodiesel operation at recommended and optimized injection timings

respectively in comparison with conventional engine.

With increase of injection pressure with both versions of the engine with test fuels.

Peak brake thermal efficiency increased. At full load operation- brake specific energy consumption decreased, exhaust gas temperature decreased, volumetric efficiency increased, coolant load increased and sound levels decreased.

With preheating of biodiesel with both versions of the engine

Peak brake thermal efficiency increased, at full load operation- brake specific energy consumption decreased, exhaust gas temperature increased, volumetric efficiency decreased, coolant load decreased, sound levels decreased.

LHR engine was more suitable for biodiesel operation than pure diesel operation.

4.1 Research Findings and Suggestions

Comparative studies on performance parameters with direct injection diesel engine with high grade low heat rejection combustion chamber and conventional combustion chambers were determined at varied injector opening pressure and injection timing with different operating conditions of the biodiesel. Experimental results were compared with pure diesel operation at similar operating conditions.

Hence further work on the effect of injector opening pressure and injection timing on exhaust emissions and combustion characteristics with LHR combustion chamber with biodiesel operation is necessary.

Acknowledgments

Authors thank authorities of Chaitanya Bharathi Institute of Technology, Hyderabad for providing facilities for carrying out research work. Financial assistance provided by All India Council for Technical Education (AICTE), New Delhi, is greatly acknowledged.

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