INTRODUCTION

The biodiesel has been used in the conventional engine by using various methods and techniques reported as many as works (Murugesan et al., 2009; Atadashi et al., 2010; Banapurmath et al., 2009). Now a day’s fossil fuels are using tremendously, but these are not promising as sustainable energy resources, because fossil fuels are decaying very soon and emits more pollutants to environment and creating the health problems on living beings. Hence it is very much necessary to switch over to utilization of alternative renewable sources (Naik et al., 2010). The advantages of diesel engine are higher BTE, outstanding drivability but they emit more quantity of particulate matters and NOx. Some of emission norms are developed by various agencies to control the pollution from diesel engines (Mani et al., 2011). To resolve all problems of CI engines, many research works has been carried out worldwide with various fuel combinations and injection strategies (Atmanli et al., 2014; Gautam and Agarwal, 2013). Trans-esterified biodiesel fuel has very stringent potential in CI engines, hence as many as countries uses the varieties of edible and non-edible oils such as palm, soybean, Jatropha curcas, pongamia pinnata and linseed biodiesel to produce the power output from CI engine (Srivastava and Verma, 2008; Balat and Balat, 2008; Dixit and Rehman, 2012; Labeckas and Slavinskas, 2006; Kannan et al., 2012). The application of such biodiesels for diesel engines were minimized the pollutants such as particulate matter (PM) emissions, carbon hydrocarbon (HC) and carbon monoxide (CO). Hence the drastic improvement was essential requirement in the field of biodiesel fueled diesel engine. The end products of tyre pyrolysis are carbon black, pyro gas and oil (Paul and Williams, 2013). A reduction of BTE, when blend ratio was increasing in standard diesel fuel reported in the literature survey (Abhishek and Murugan, 2013). As per report of experiment depicted that reduces the CO, smoke level and HC emissions when addition of Desulfurized tyre oils mixed with diesel, but comparatively diesel has lower emission than mixed oil (Aydın and Ilkılıc, 2015). When plastic oil blends with diesel gives higher SFC than diesel and higher of CO, NOx and CO₂emissions were observed (Pratoomyod and Laohalidanond, 2013). Many research works have been carried on CI engine by using several biofuels with different injection strategies as IT and IOP. By advancement or retardation in IT, there was enormous changed in combustion parameters has been observed (Hountalas et al., 2001). As retarding the IT in CI engine, the NOx pollutant has been reduced when operated with biodiesel and diesel fuels (Hountalas et al., 2001; Tao et al., 2005). The tremendous cylinder pressure and temperature were decreased has been observed when IT was retarded in CI engine (Roy, 2009). The IT effect was observed at advanced IT of 40 °BTDC when waste cooking oil operated as biofuel in CI engine and reported that better BTE and reduced pollutants (Bari et al., 2004). Honge biodiesel has been reported that the performance of CI engine improved by retarding the IT (Banapurmath et al., 2008). The engine performance has been improved by enhancing the IOP up to 230 bar and retarding the IT, when cotton methyl ester operates in CI engine (Rosli et al., 2008; Banapurmath et al., 2012). The experimental results showed that the pollutants CO, PM and HC emissions were minimized by the percentage of 14.2%, 13.26% and 9.3% respectively, when CI engine operated with JOME and pyrolysis blend at advanced IT condition of 24.5 °CA BTDC (Sharma and Murugan, 2015). In the same way, by enhancing the IOP with various fuel combinations would result better performance of IC engine were reported by many experimental research works (Roy 2009; Banapurmath et al., 2008; Rosli et al., 2008; Sukumar et al., 2009; Suresh et al., 2013).

The various research works have been carried out on CI engine with modification of nozzle holes geometry operated with biodiesel fuel. Ten holes nozzle geometry performed well in terms of better atomization and reduction of NOx emission in diesel engine at full load condition (Karra et al., 2010). Suggested that by varying number holes in nozzle injector reducing the oxides of nitrogen in biodiesel fuelled diesel engine and minimize the unburnt hydrocarbon, carbon monoxide and brake specific fuel consumption (Lahane et al., 2014). By varying the injection timing, injection pressure, CR and nozzle holes leads to enhance the performance parameters like brake thermal efficiency, meanwhile reduced the emission characteristics in biodiesel fuelled diesel engine but however oxides of nitrogen emission has been increases as number of holes increase in injector nozzle (Khandal et al., 2015). Suggested that, retarded IT of 19 °bTDC, IOP of 230 bar and four-hole nozzle injector were optimized injection parameters for higher BTE with lower emissions operated with HOME, HnOME and COME fuels in CI engine (Wategave et al., 2014). Many research works have been carried out by modification in both combustion chamber shapes and injection strategies. The experimental results were observed in CI engine operated with Pongamia biodiesel fuel, the BTE of engine has improved as compared to baseline HCC shape (Jaichandar and Annamalai, 2012). The experimental work has been reported that, both BTE and SFC were improved in CI engine operated with Pongamia biodiesel fuel for combination of TRCC shape and higher injection pressure (Jaichandar and Annamalai, 2013). Torroidal combustion chamber shape showed higher performance parameters with reduced emission characteristics compared to Cylindrical, trapezoidal combustion chamber shapes in diesel engine (Banapurmath et al., 2015). The combined effect of cylindrical combustion chamber shape and nozzle geometry reduced the NOx emission up to 45% as compare to baseline geometry, but reduced slightly in BTE parameter was observed in biodiesel fuelled diesel engine (Shivashimpi et al., 2017). Cylindrical combustion chamber shape performed better BTE up to B60 blend and 40% reduction of NOx was observed as compared to base line geometry in biodiesel fuelled diesel engine (Shivashimpi et al., 2016). By the modification combustion chamber shape led to the reduced emission characteristics but performance parameters remain same was observed in diesel engine (Mobasheri et al., 2013). By using combine effect of multi-chambered combustion chamber shape and 200 bar nozzle injection pressure showed better performance and reduced emissions in diesel engine operated with Jatropha biodiesel fuel (Rajashekhar et al., 2012). TRCC shape resulted higher BTE, reduction of SFC and emission characteristics at retarded injection timing compared to baseline combustion chamber shape when diesel engine operated with Ultra sulphur diesel fuel (Jaichandar et al., 2012). The engine operated with HOME – producer gas resulted increase in 4-5% of BTE and reduced emissions with TRCC shape, 230 bar IOP and 4-hole nozzle geometry (Yaliwal et al., 2016). The BTE of Toroidal combustion shape found higher in performance but slightly lower in emissions parameters as compared with spherical and Toroidal re-entrant combustion shape operated with 20% JTME in diesel engine (Mamilla et al., 2013). The BTE has improved by Toroidal combustion chamber with tangential cut on circumference of the piston crown and reduced emissions were observed at 200 bar IOP 25 °BTDC IT as compared with base line shape in diesel engine (Kumar, 2017). The experimental investigation showed that higher BTE resulted for up to B40, B20 of POME blends in base line and modified CCC shapes respectively in diesel engine. In the same way, drastic reduction of UBHC and NOx emissions were observed in modified SCC and TCC shapes as compared to base line shape (Shivashimpi et al., 2018). The experimental report showed that in diesel engine, the fuel IT of 27 °BTDC, IOP of 240 bar, 5 holes nozzle geometry with Toroidal Re-entrant combustion chamber shape gave BTE with nominal emissions (Shivashimpi et al., 2018).

Now day’s research woks were carried for CI engine by adopting CRDI technology. CRDI technology has very suitable for CI engine to improve the performance and reduce the emissions of engine. Many research woks have been conducted the experiments on CRDI engine with operating both diesel and bio derived fuels. The obtained results were compared with conventional CI engine. The CRDI diesel engine operated with Tung oil-diesel-ethanol blends has been improved engine efficiency and reduced emissions, but slightly NOx increased as compared to diesel (Qi et al., 2017). At 880 bar IOP was operated in the CRDI engine with mahua methyl ester blend showed better combustion performance and reduced HC, CO and smoke emissions (Aalam et al., 2016). The harmful pollutants have been decreased when biodiesel blend with nanoparticles in CRDI diesel engine (Aalam et al., 2017). Reduced emissions were observed for IP from 600 to 1200 bar in CRDI engine (Grimaldi et al., 2000). 40% of particulate matter was reduced by using post and multiple injection strategies in CRDI diesel engine and improved addition combustion performance was also observed (Chen, 2000). Combustion process in CRDI diesel engine has mainly depended on the pilot injection; timing and quantity were observed (Bandai et al., 2001). Experiments were conducted the on common rail HSDI diesel engine operate with rape seed methyl ester (RME) showed lower CO, smoke and HC emissions and slightly increase in the NOx levels. Performance and combustion characteristics were slightly lower for RME compared diesel was observed (Carlo et al., 2002). CRDI diesel engine IP affects the all the injection parameters like delivery of fuel, its duration and quantity under all modes of injection fuel strategies (Henein et al., 2002). The optimized engine variables like start of injection, injection duration and air fuel ratio were enhancing the power, lower bsfc and reduced emissions in CRDI diesel (Soorajith and Vinu, 2004). By varied the injection angles and increased the injection pressure were resulted faster combustion rate in combustion chamber along with increased NOx emission for CRDI engine (Fang and Lee, 2009). CRDI CI engine powered with karanja biodiesel was improved in thermal efficiency and reduced emissions up to 10% of blend (Agarwal et al., 2015). Advanced start of injection timing showed higher performance, better combustion characteristics and lower bsfc and increased NOx was observed in CRDI CI engine (Agarwal et al., 2015). The CRDI mode diesel engine operated with HOME and COME BDF’s gives the better performance and reduced with smoke and NO_x emissions as compared to conventional diesel engine, when 7 holes CRDI injector, TRCC, 900 IOP and 10° BTDC have been adopted in engine (Khandal et al., 2018). The diesel engine run with CRDI mode gave the reduced emissions of CO, HC and smoke except CO₂ and NO_x (Karthikeyan et al., 2018). The CRDI diesel engine showed that lower opacity for advanced combustion mode as compared to conventional diesel engine (Iorio et al., 2018) The CRDI operated diesel engine tested with plastic liquid fuel blends obtained from the municipal waste plastic pyrolysis process. The CRDI engine operated with plastic liquid blend showed improved performance than mineral diesel operation. Slightly, the emissions have been improved towards CO, HC and NO_x emissions (Shettyet et al., 2016). Thermal efficiency of CRDI diesel engine decreases up to 30% of plastic oil blend than diesel, but CO was increasing with increases in blend and CO₂ and NO_x were decreases as increasing in the blend (Shukla et al., 2016). The diesel engine with CRDI mode showed that B20 blend emitted lower primary particulates matter in comparison with mineral diesel at all loads (Shukla et al., 2014)

From exhaustive literature survey revealed that, experimental work was scantily carried on combined effect of IOP, IT, nozzle geometry and TRCC shape in CRDI diesel engine operated with POME as alternative fuel. Hence, experimental research investigation progressed herewith choosing POME as biodiesel and various IT and IOP with using TRCC shape and 6 hole injector for CRDI mode diesel engine.

Objective of the Work

The objective of research work is to optimize the injection timing and injection pressure for improve overall efficiency of CRDI diesel engine using TRCC shape and 6 holes CRDI injector operated with POME as a biodiesel fuel and compared performance, combustion and emission characteristics results of modified CRDI diesel engine operated with POME and diesel fuels.

PRESENT WORK

The present work basically involves the determination of POME biodiesel fuel properties and comparison with standard mineral diesel fuel. Effect of combustion chamber shape i.e., Toroidal re-entrant combustion chamber shape with 6 holes CRDI injector on the performance of diesel engine fuelled with for higher efficiency and lower emission of engine. Finally, comparison of results between modified CRDI diesel engine operated with POME and diesel fuels.

MATERIALS AND METHODS

The above section mainly discussed the materials and methodology has been adopted for the experiment.

The Details of POME Properties

The important properties of POME are enlisted blow in the Table 1, the properties are measured using the lab facility.

Experimental Set-up and Methodology

The experimental setup along with CRDI facility used in CI engine is shown in Figure 1. Diesel engine developing BP 5.2 kW was suitably modified with CRDI mode to operate with high injection pressure along with POME as alternative fuel biodiesel. The CRDI system has been established in house and controlled by electronic control unit (ECU) shown in Figure 2. ECU system makes easy to operate the CRDI diesel engine for biodiesel injections at different ITs and IOPs. The present experiments were carried out with variations in IT and IOP to optimize the CRDI diesel engine operation with POME. The experiments were conducted in the two parts, first part of experiment was carried by varying the IT from 25 °CA bTDC to 5 °CA aTDC in interval of 5 °CA. Finally, the fuel IT was optimized at 80% engine loading conditions. The engine speed, IOP were maintained constant at 1500 rpm and 600 bar respectively by regulating speed and flow rate of pump in the CRDI engine. Optimized value of 10°CAbTDC IT was obtained. In the second experiment, IP was varied from 600bar to 1000 bar with constant IT in CRDI engine. The maximum 1000 bar pressure was attained in the system due to limitation of hardware capacity. ACRDI injector of6-hole nozzle injector with 0.2 mm diameter has been used for engine setup, TRCC shape combustion chamber was used to improve the mixing quality between POME and air were shown in Figure 3. Hence CRDI injector and modified combustion shape were potentially suitable for power output in CI engine. The important specification of experiment test rig showed in the Table 2. Cooling of engine was maintained by the supplying the water through the water jackets using pump. A piezoelectric transducer (Make: PCB Piezotronics, Model: HSM 111A22, Resolution: 0.145 mV/kPa) was utilized for measurement of pressure, which was connected to cylinder head and specifications and connected to the cylinder head was utilized to measure the in-cylinder gas pressure. Figure 4 shows Hartridge smoke meter for smoke emission determination and five-gas analysers (A DELTA 1600 S-non-dispersive infrared analyzer) to measure HC, CO, CO₂, NOx and O₂under steady state condition of engine operating conditions. Important specification of exhaust analyser and smoke meter are shown in Table 3. The TRCC shape of combustion chamber is developed by using CNC machines keeping the same CR between base line and modified shapes. The Optimum parameters of engine operated with POME were established based on the properties of fuel and results of experiments in engine.

Figure 1. Schematic diagram of experimental set up and CRDI facility in modified CI engine

Figure 2. ECU connection with CRDI Engine Test Rig

Figure 3. CRDI Injector (6 holes) and Toroidal Re-entrant Combustion Chamber Shape

Figure 4. Exhaust Gas Analyzer and Smoke meter

Uncertainty Analysis

The uncertainties are most common in the measurement and parameter calculation, precise list of uncertainties calculated parameters are showed in the Table 4.

RESULTS AND DISCUSSION

Optimization of Fuel IT for CRDI Diesel Engine

The rigorous experiments have been performed on the CRDI diesel engine with diesel and POME fuels. The re-entrant combustion chamber chosen for experiment, 17.5: 1 CR has kept constant; engine has made to run at constant speed 1500 rpm. The fuel IT has been optimized with varied fuel IT from 25 °CAbTDC to 5 °CA aTDC with steps of 5 °CA for 80% and 100% engine load condition. The IOP 600 bar is kept constant in CRDI engine for all the fuel IT of engine with 6 holes 0.2 mm diameter CRDI injector. For the study 80% and 100% engine were selected and discussed results of performance, combustion and emission characteristics.

IT Effect on BTE

The effect of injection timing with BP at 80% and 100% loads operating with POME and diesel fuels in CRDI engine shown in Figure 5. As per obtained results depicted that maximum BTE showed at 10 °bTDC for POME biodiesel. The maximum BTE of POME fuel at 10 °bTDC due to the improved atomization of POME at 600 bar. The better mixing strength is also one of the reasons to improved BTE. The wall wetting has been reduced leads to improved burning rate of fuel leads to improve the BTE of the engine operated with POME. The CRDI engine was affecting in its efficiency by retarding or advancing the fuel IT. By retardation of IT, reduced BTE due to more amount of fuel entered in to crevice leads to decrease in available time for mixing fuel-air. On other hand, by advancing the fuel IT leads to reduced BTE due to increased wall wetting at higher IOP. At 80% load, BTE were 28, 30.56% for POME and diesel respectively at 10°bTDC IT. Similarly, at 100% load, 27.5, 30% for POME and diesel respectively at 10°bTDC IT. By results higher BTE obtained for diesel compared to POME due to higher calorific and lower viscosity of mineral diesel fuel at10 °bTDC IT and 80% load under engine conditions 6-hole CRDI injector, TRCC shape with 600 bar IOP in CRDI engine. For 100% load slightly BTE has been reduced due to negating effect in the engine.

Figure 5. Effect of fuel IT on BTE for POME and Diesel fuels at 80% load and 100% load

IT Effect on Smoke Opacity

From Figure 6 illustrates that the effect of injection timing with smoke opacity at 80% and 100% loads operating with POME and diesel fuels in CRDI engine. Smoke level of diesel has lower as compared to POME in the CRDI engine due to the heavier presence of FFA in the POME. The higher viscous nature of the POME leads to loose the mixing quality in the combustion chamber. The smoke level of both fuels has been showed decreasing trend up to 10 °bTDC at 600 bar due to wall wetting was reduced. Hence, combustion process of both fuels was improved for higher BTE and formation of oxidation reactions in the combustion chamber. But beyond 10°bTDC increasing in the smoke intensity was observed due to the rate of mixing of air and fuel quality has been reduced leads to slow combustion rate formation. However, smoke intensity of POME higher than the diesel fuel in CRDI engine due to higher viscosity. The results formed for smoke levels were 47, 32 HSU for POME and diesel respectively at 80% load and 10°bTDC. Similarly, for 100% load obtained results were 66, 40 HSU for POME and diesel respectively at 10°bTDC. However, smoke intensity of POME higher than the diesel fuel in CRDI engine due to poor mixing characteristics at 10°bTDC under engine conditions of 80% load, 6-hole CRDI injector, TRCC shape with 600 bar IP in CRDI engine.

Figure 6. Effect of fuel IT on smoke for POME and Diesel fuels at 80% load and 100% load

IT Effect on HC and CO Emissions

From Figures 7 and 8 depicted that the effect of fuel IT with HC, CO emissions for POME and diesel at 80%, 100% loads for CRDI engine. The POME fuel operated CRDI engine resulted higher HC and CO emissions than diesel fuel due to poor quality of air fuel mixture. The presence of heavier molecular structure in POME fuel leads to bigger size of fuel particles, hence poor combustion of POME could be the reason to higher emissions at 600 bar. The emissions like HC, CO were out by engine minimum at 10 °bTDC IT due to improved combustion of fuel droplet size at constant 600 bar and higher BTE occurred. However, CO and HC emissions were higher for other fuel IT due to improper combustion. The advanced fuel IT behind the 10°bTDC leads to increase in wall wetting of combustion chamber, by retarding the fuel IT beyond the 10 °bTDC leads to more amount fuel injecting in to crevice that is loss of power in the engine. HC emissions obtained at 80% load were 46, 36 ppm for POME and diesel fuels respectively for CRDI mode at 10°bTDC. Similarly, at 100% load 60, 50 ppm for POME and diesel fuels respectively for CRDI mode at 10 °bTDC. CO emissions obtained at 80% load were 0.16, 0.13% for POME and diesel fuels respectively for CRDI mode at 10°bTDC. Similarly, at 100% load 0.22, 0.18% for POME and diesel fuels respectively for CRDI mode at 10 °bTDC. However, the HC and CO pollutants were optimized at 10 °bTDC IT for POME and diesel fuels under the engine conditions of 600 bar, 6-hole CRDI injector with TRCC shape.

Figure 7. Effect of fuel IT on HC for POME and Diesel fuels at 80% load and 100% load

Figure 8. Effect of fuel IT on CO for POME and Diesel fuels at 80% load and 100% load

IT Effect on NOx Emissions

Figure 9 revealed that the variation of fuel IT with NOx at 80% and100% loads for POME and diesel fuels in CRDI engine. Peak Pressure and Heat release rate were increased in both cases of loads and fuels due to presence of longer ID. Hence, there was enhanced nature in NOx emissions at advanced fuel IT behind of 10 °bTDC. This peak NOx emission was obtained due to higher exhaust peak temperature occurred in the cylinder. In both loads, decreasing trend of NOx emission was observed for retarded IT in CRDI mode. The NOx emission obtained at 80% load were730, 800 ppm for POME and diesel respectively at fuel IT of 10° bTDC. Similarly, at 100% load 770, 825 ppm for POME and diesel respectively at fuel IT of 10 °bTDC. However, minimized NOx emissions has been observed for POME fuel compared to diesel fuel due to lower cetane number leads to decreased in gas temperature at 10 °bTDC, 80% load, 600 bar IP and 6-hole CRDI injector in CRDI diesel.

Figure 9. Effect of fuel IT on NOx for POME and Diesel fuels at 80% load and 100% load

IT Effect on Ignition Delay

Figure 10 depicted that the variation of ID with crank angle for POME and diesel at 80%, 100% loads in CRDI engine. In both cases of loads, ID was decreasing trend up to 10 °bTDC IT, then it increased further due to higher gas temperature. However, the POME showed higher ID as compared to diesel fuel due to lower cetane number of POME fuel for both loading conditions of CRDI engines at 10 °bTDC IT, 600 bar. This result could be the heavier molecular structure of POME leads slow combustion rate in the combustion chamber. At 80% load ID results were 14.01, 13.4 °CA for POME and diesel fuels respectively at 10 °bTDC IT. Similarly, at 100% load 13.72, 13.12 °CA for POME and diesel fuels respectively at 10 °bTDC IT. The 80% load of ID has been optimized with CRDI mode, 6-hole CRDI injector, 600 bar, 10 °bTDC and TRCC shape due to higher BTE.

Figure 10. Effect of fuel IT on NOx for POME and Diesel fuels at 80% load and 100% load

IT Effect on Combustion Duration

The variation of combustion duration with crank angle for POME and diesel fuels at 80%, 100% loads in CRDI diesel engine illustrated in Figure 11. As retarding the fuel IT, CD was tends to deceases up to 10 °bTDCIT, further again increased CD was observed for both the fuels with 80% and 100% loads. This is due to higher gas temperature generated in the combustion chamber up to 10 °bTDC IT. Further rise of temperature is decreases by retardation of fuel IT due to lower low burning rate of fuel may be reason. CD obtained at 80% load were 31, 28 °CA for POME and diesel fuels respectively at 10 °bTDC IT. Similarly at 100% load 34, 31 °CA for POME and diesel fuels respectively at 10 °bTDC IT. However, POME exhibited higher CD compared to diesel due to lower energy content and higher viscosity are could be the reason at 10 °bTDC IT, 600 bar, 6 hole CRDI injector and TRCC shape for 80% load in CRDI engine.

Figure 11. Effect of fuel IT on CD for POME and Diesel fuels at 80% load and 100% load

IT Effect on Peak Pressure

From Figure 12 depicted that the variation of Peak Pressure with crank angle for POME and diesel fuels at 80%, 100% loads in CRDI diesel engine. In both the loads, POME and diesel fuels of peak pressure were decreasing trend as retarding the fuel IT due to reduced ID period in CRDI engine. In contrast of advancing the fuel IT, higher peak pressure was observed due to more available fuel quantity during chemical reaction in diffused combustion stage. The results of Peak Pressure were 72, 74 bar obtained for POME and diesel fuels respectively with at 10 °bTDC with 80% load. Similarly, 75, 79 bar for POME and diesel respectively at 10 °bTDC with 100% load. However, POME fuel has been observed lower peak pressure than diesel fuel due to lower calorific of POME fuel. This leads to reduced mixing quality of fuel and air r in the combustion chamber at 10 °bTDC IT, 600 bar, 6 hole CRDI injector and TRCC shape for 80% load in CRDI engine.

Figure 12. Effect of fuel IT on PP for POME and Diesel fuels at 80% load and 100% load

IT Effect on Heat Release Rate

Variation of HRR with crank angle for POME and diesel fuels at 80%, 100% loads in CRDI diesel engine illustrated in Figure 13. In both the loads of engine condition, Heat release rate of POME and diesel fuels were higher at advanced fuel IT due to maximum availability of fuel. Hence, it enhances the chemical reactions in the diffused combustion zone of combustion process. The drop of HRR was observed for both fuels in CRDI engine due to more quantity of fuel wall wetting leads to reduced burning rate of fuel during retarding the IT. The results of HRR were 65, 70 J/°CA obtained for POME and diesel respectively with at 10 °bTDC with 80% load. Similarly, 82, 88 J/°CA for POME and diesel fuels respectively at 10 °bTDC with at 100% load. However, POME exhibited the lower HRR than diesel due to lower energy content of fuel could be the reason. The 80% load of HRR has been optimized for POME with CRDI mode, 6 hole CRDI injector, 600 bar, 10 °bTDC and TRCC shape due to higher BTE.

Figure 13. Effect of fuel IT on HRR for POME and Diesel fuels at 80% load and 100% load

Optimization of IOP for the Diesel and POME Fuels in CRDI Engine

With reference to first part of experiment results of research work, the 80% load and 10°bTDCIT were optimized for higher BTE and minimized emissions for the CRDI engine powered with POME and diesel fuels under the engine conditions of 6-hole CRDI injector, constant 600 bar IOP and TRCC shape. However, the variation IOP was influencing very significantly on CRDI engine performance operating with alternative fuels. Hence for current studied, IOP varied from 600 to 1000 bar in the interval of 100 bar for POME and diesel fuels with optimized fuel IT constant at 10°CA bTDC. The engine speed was maintained at 1500 rpm. For the study, 80 & and 100% load were selected along with 6 holes (0.2 mm diameter) CRDI injector and TRCC shape were chosen.

IOP effect on BTE

From Figure 14 illustrated that effect of IOP on BTE operated with diesel and POME fuels in CRDI engine at 80% load and 100% load. The BTE has been increased up to 900 bar IOP and later reduction of BTE trend was observed for both fuels due to negating effect of engine. The atomization spray characteristics have been improved by increasing the IOP from 600 bar to 900 bar. This leads to formation of homogeneous mixture in the combustion chamber and reduced ignition delay at higher pressure could be the reason to raised BTE. The viscosity of fuel is to reduce at higher pressure of fuel injection. The reduced viscous fuel easily mixes with air and fuel leads to improve the combustion process in the combustion chamber. The BTE of engine has been decreased at 1000 bar IOP due to more fuel wall wetting. However, BTE has higher at IOP 900 bar due to higher fuel penetration of fuel and increased fuel dispersion in the combustion chamber. Thermal efficiency of diesel value has more compare to POME at 900 bar due to presence of lower cetane number, higher FFA and lower volatility. The HRR of POME has lesser than the base line fuel (diesel) under same conditions of engine. The results of BTE obtained at 80% load and 900 bar were 28.75, 32% for POME and diesel respectively. Similarly, at 100% load and 900 bar 28.6, 31.6% for POME and diesel respectively. Finally, POME resulted higher BTE at 80% load with CRDI mode at the engine conditions of 900 bar, 10 °bTDC, TRCC shape and 6 holes CRDI injector.

Figure 14. Effect of BTE on IOP for POME and Diesel fuels at 80% load and 100% load

5.2.2 Effect of IOP on Smoke Level

Figure 15 showed that the effect IOP on BTE with smoke level in CRDI engine for POME and diesel at 80% and 100% load. The POME fuel has been resulted greater smoke level than diesel due to presence of both higher weighted molecular structure and viscosity. The POME exhibited unsuitable air-fuel mixture in the combustion chamber leads to increased smoke emissions for POME than base line fossil fuel. The POME fuel showed reduced emissions up to 900 bar IOP due to better atomization of fuel particles leads to enhanced combustion process in the combustion chamber. The smoke level results were 29, 40 HSU for diesel and POME at 900 bar and 80% load. Similarly, for 100% load 36 and 50 HSU for diesel and POME respectively at 900 bar. By comparison of both loads, 80% load was optimized for lower smoke level under engine conditions of 900 bar, 10 °bTDC, TRCC shape and 6 holes CRDI injector for CRDI diesel engine.

Figure 15. Effect of smoke level on IOP for POME and Diesel fuels at 80% load and 100% load

Effect of IOP on HC and CO emissions

The Figures 16 and 17 depicted that the variation of IOP on HC, CO emissions for POME and diesel fuels at 80% load and 100% load of CRDI engine. Usually for higher IOP, decreasing trend of CO and HC emissions have been observed for both fuels and loads. This result could be a reason for better atomization and enhancing complete combustion rate of injection fuel in the combustion chamber. Due to presence of higher oxygen content and proper burning rate in POME leads to decreased trend of emissions (HC and CO) at 900 bar IOP. But the emissions slightly higher for POME compare to mineral diesel in CRDI diesel engine due to higher viscosity could be the reason. The HC and CO emissions out from engine were higher for 1000bar due to increased wall wetting phenomenon and also the fuel spray emerging in larger distance in CC could be the reason for both fuels and loads at higher pressure. HC emissions were 37 and 30ppm for POME and diesel respectively at 80% load and 900 bar IP. Similarly, for 100% load, 53 and 44ppm for POME and diesel fuels respectively at 900 bar IP. CO emissions obtained were 0.145 and 0.12% for POME and diesel fuels respectively at 80% load respectively and 900 bar IP. Similarly at 100% load 0.205 and 0.171% for POME and diesel fuels respectively at 900 bar IP. By the results, 80% load was optimized for lower HC and CO emissions under engine conditions of 900 bar, 10 °bTDC, TRCC shape and 6 hole CRDI injector for CRDI diesel engine.

Figure 16. Effect of HC on IOP for POME and Diesel fuels at 80% load and 100% load

Figure 17. Effect of CO on IOP for POME and Diesel fuels at 80% load and 100% load

Effect of IOP on NOx Emissions

From the Figure 18 revealed that the variation of IOP on NO_x emissions for POME and diesel fuels at 80% load and 100% load of CRDI engine. Due to improved atomization and dispersion characteristics of fuel leads to enhanced combustion rate. Hence gas temperature increased in the cylinder at higher injection pressure of fuel. Diesel fuel depicted that higher NOx emission from engine compared to POME fuel due to POME has lower viscosity and higher density value. There are two factors affecting for the better mixing strength of air and fuel mixture. These factors were dispersion fuel quality and smaller size of fuel droplets led to decreased in ID. Hence HRR has been more in quantity at higher operating pressure of IP (900 bar), that enhances the higher gas temperature with formation more NO_x out from engine. By the observed results depicted that, NO_x out from engine with respect to POME fuel could be lower emissions due to premixed combustion phase stage was lower as compared to fossil diesel fuel. The arising the lower adiabatic flame temperature in the combustion chamber and lower CN of POME were reasons to lower NO_x emission from engine. The NO_x emissions obtained were 784 and 850 ppm for POME and diesel fuels respectively at 80% load and 900 bar IP. Similarly, at 100% load 814 and 875 ppm for POME and diesel respectively at 900 bar IP. Form the results observed that, the 80% load was showed the higher NO_x for CRDI diesel engine under engine conditions of 900 bar, 10°bTDC, TRCC shape and 6 holes CRDI injector.

Figure 18. Effect of NOx on IOP for POME and Diesel fuels at 80% load and 100% load

Effect of IOP on Ignition Delay

From the Figure 19 illustrated that the variation of ID with IOP for POME and diesel fuels at 80% and 100% load in CRDI engine. The reduced ID was observed by increasing the injection pressure for both the loads due to better burning rate of fuels. The increased ID was observed beyond the 900 bar IP due to higher wall wetting led to lower mixture quality. Because of higher BTE consideration for 80% load, the results for ID were10.3, 9.6 °CA for POME and diesel respectively at 900 bar IP. Similarly for 100% load, 10.92, 10.2 °CA for POME and diesel respectively at 900 bar IP. However, lower ID for diesel as compare to POME was observed in both loads at higher IOP due to higher energy content in mineral diesel fuel under engine conditions of 900 bar, 10 °bTDC, TRCC shape and 6 hole CRDI injector for CRDI diesel engine.

Figure 19. Effect of ID on varied IOP for POME and Diesel fuels at 80% load and 100% load

Effect of IOP on Combustion Duration

From the Figure 20 depicted that the variation of CD with IOP for POME and diesel fuels at 80% and 100% load in CRDI engine. The fuel droplet size has been reduced by increasing the injection pressure due better atomization of fuel. Hence CD was decreased trend up to 900 bar for both the loads due to better burning rate of fuels. The increased CD was observed beyond the 900 bar IP due to higher wall wetting led to lower mixture strength quality. The consideration of higher BTE at 80% load, the results for CD were 28, 25°CA, for POME and diesel respectively at 900 bar IP. Similarly, for 100% load, 30 and 27 °CA for POME and diesel respectively at 900 bar IP. However, lower CD for diesel as compare to POME was observed in both loads at higher IOP due to lower viscosity in mineral diesel fuel under engine conditions of 900 bar, 10 °bTDC, TRCC shape and 6-hole CRDI injector for CRDI diesel engine.

Figure 20. Effect of CD on varied IOP for POME and Diesel fuels at 80% load and 100% load

Effect of IOP on Peak Pressure

From the Figure 21 depicted that the variation of peak pressure with IOP for POME and diesel fuels at 80% and 100% load in CRDI engine. The peak pressure was raised up to 900 bar IP due to better fuel atomization and reduced ID are could be the reasons. The Peak Pressure was shown decreased trend beyond 900 bar due to more quantity of fuel entered in the crevices leads to inadequate combustion process in the combustion chamber. For 80% load, the results for PP were 79, 83 bar, for POME and diesel respectively at 900 bar IP. Similarly, for 100% load, 82, 87 bar for POME and diesel respectively at 900 bar IP. However, higher PP for diesel as compare to POME was observed in both loads at 900 bar IP due to lower viscosity in mineral diesel fuel under engine conditions of 900 bar, 10°bTDC, TRCC shape and 6 holes CRDI injector for CRDI diesel engine.

Figure 21. Effect of PP on varied IOP for POME and Diesel fuels at 80% load and 100% load

Effect of IOP on Heat Release Rate

From the Figure 22 illustrated that the variation of HRR with IOP for POME and diesel fuels at 80%, 100% load in CRDI engine. The heat release rate was raised until 900 bar IP by enhancing the CRDI nozzle injector pressure due to better fuel atomization. The reduced ID was the reason to raise the heat release rate at higher injection pressure. The HRR was shown decreased trend by further increasing in pressure due to more quantity of fuel entered in the crevices leads to inadequate combustion process in the combustion chamber. For 80% load, the results for HRR were 73, 79J/°CA, for POME and diesel respectively at 900 bar IP. Similarly, for 100% load, 89 and 97 J/°CA for POME and diesel respectively at 900 bar IP. However, higher HRR for diesel fuel as compare to POME fuel was observed in both loads at 900 bar IP. This due to POME has higher viscous than diesel led to more friction formed in the injector needle. Hence, there was hinders in valve lifting movement leads to longer ID in POME operation. So reduced HRR was obtained in the engine under conditions of 900 bar, 10 °bTDC, TRCC shape and 6 holes CRDI injector for CRDI diesel engine.

Figure 22. Effect of HRR on varied IOP for POME and Diesel fuels at 80% load and 100% load

CONCLUSIONS

From entire exhaustive experimental work conducted for POME and diesel fuels for 80% and 100% load in CRDI diesel engine. The 80% engine load was optimized for higher efficiency of engine. Hence the following conclusions were made for 80% engine load only:

• When CRDI diesel engine operated with POME has resulted maximum BTE under following the engine conditions were 10°bTDC fuel IT, constant IP 600 bar, 6 holes CRDI nozzle geometry and 17.5 CR with TRCC shape.

• When CRDI diesel engine operated with POME at optimized 10° bTDC fuel IT, BTE was increased and reduced emissions for 900 bar IP as compared to other IP with 6 holes CRDI injector, TRCC shape for constant CR.

• On overall, CRDI diesel engine operated with POME as alternative fuel resulted higher BTE and lower emissions under engine conditions of 900 bar IP, 10 °bTDC fuel IT, TRCC shape and 6 holes CRDI injector with CR constant 17.5. By using POME as alternative fuel for CI engine with slight modification of engine helps to resolve all possible problems were raised from fossil fuel throughout world.

NOMENCLATURE