Effect of injection parameters on the performance and emission characteristics of a variable compression ratio diesel engine with plastic oil blends

Abstract

Due to the depleting fossil fuel reserves and increasing environmental concerns, researchers have been studying the effect of adding different types of oils to diesel and more recently plastic oil. The present paper is an experimental study of the effect of compression ratio and injection parameters such as injection pressures and injection timing on the performance and emission characteristics of a variable compression ratio diesel engine fuelled with blends of plastic oil. Various proportions of ethanol and diesel are blended with plastic oils for the preparation of test fuels. It is observed from the experimental study that P90D5E5 blend gives the highest brake thermal efficiency yielding an increase of 16% and 38% compared with pure diesel and pure plastic oil, respectively. Smoke emissions are found to be the lowest for P90D5E5 than diesel and P100. Brake-specific fuel consumption, carbon monoxide and smoke values are reduced for all blends with an increase in injection timing, pressure and compression ratio. Combustion analysis of the blends indicates higher values of cylinder pressures and net heat release rates for P90D5E5 and P100, respectively.

Keywords

Variable compression ratio engine waste plastic oil emissions injection parameters

Introduction

The depletion of fossil fuel reserves and their increasing demand makes the survival of automobiles questionable every day. In this situation many alternative fuels like biodiesels, methanol, ethanol and synthetic fuels like plastic oils look promising to sate the thirst of automobiles in the future. Waste plastic is used as a raw material for the production of plastic oil which is abundantly available and helps in recycling. In this scenario considerable amount of research has been done on alternative fuels starting from biodiesels to the synthetic oils. Raheman and Ghadge¹ studied the performance of Ricardo E6 engine using biodiesel obtained from Mahua oil and its blend with high speed diesel by varying the compression ratio (CR), injection timing (IT) and load. They reported that brake-specific fuel consumption (BSFC) and exhaust gas temperature (EGT) increase whereas brake thermal efficiency (BTE) decreases with an increase in proportions of blends of biodiesel at all CRs and ITs. The BSFC decreases while BTE and EGT are increasing with the increase of load for all the ranges of CRs and ITs. Sayin and Gumus² investigated the cinfluence of CR and injection parameters such as IT and injection pressure (IP) on the performance and emissions of a DI diesel engine using biodiesel. They report that the best results for BSFC, BSEC and BTE are observed at an increase of the CR, IP and original IT. Also, BSFC, brake-specific energy consumption (BSEC) and oxides of nitrogen (NOx) emissions increase whereas BTE, smoke opacity (OP), carbon monoxide (CO) and hydrocarbon (HC) emissions decrease with an increase in the percentage of biodiesel in the fuel mixture. Muralidharan and Vasudevan³ studied the impact of CR on the performance, emission and combustion characteristics of a single cylinder four-stroke variable compression ratio (VCR) engine when fuelled with waste cooking oil methyl ester. They found that for the blend B40 at 50% load maximum BTE, a reduction in CO, HC and increase in NOx when compared with pure diesel. Labecki et al.⁴ studied the combustion and emission characteristics of rapeseed plant oil (RSO) and its blends with diesel fuel in a multi-cylinder direct injection (DI) diesel engine. They carried out the work by varying injection parameters such as IPs and timing to reduce the soot emissions for blends of 50 and 30% RSO in diesel. The exhaust soot particle number concentrations for 30% RSO blend reduce with an increase in IP and retarded IT. Bari et al.⁵ studied the effects of preheating of crude palm oil (CPO) on fuel injection, performance and emission characteristics of a diesel engine. They concluded that the CPO produces a higher peak pressure of 6%, a shorter ignition delay of 2.6°, a lower maximum heat release rate and a longer combustion period as compared to diesel. The CO and NOx emissions are found to be, respectively, 9.2 and 29.3% higher for CPO when compared with diesel. Lapuerta et al.⁶ studied diesel emissions from biofuels derived from Spanish potential vegetable oils. They proved that the use of these vegetable oil esters provides a significant reduction in particulate emissions and NOx emissionsIlkilic⁷ found that diesel engine fuelled with a blend of 25% sunflower oil methyl ester and 75% diesel has better emission characteristics than that with diesel. Nwafor⁸ results showcased that rapeseed methyl ester and its blends with diesel emitted high CO₂ emissions when compared with diesel and also a significant reduction in HC emissions is noticed. HC emissions are found to increase with the increase of diesel in the blend. There is no difference in the EGTs of the blends. Pandian et al.⁹ investigated the effect of injection system parameters such as IP, IT and nozzle tip protrusion on the performance and emission characteristics of a twin cylinder engine fuelled with pongamia biodiesel blended with diesel. They reported an IP of 225 bar, IT of 21° before top dead centre (BTDC) and 2.5 mm nozzle tip protrusion as optimal values for the pongamia biodiesel-blended diesel. Sayin et al.¹⁰ experimentally investigated the effects of IP and timing on the performance and emission characteristics of a DI diesel engine using methanol-blended diesel. They reported that an increase in the amount of methanol in the fuel blend results in the increase of BSFC, BSEC and NOx emissions but a decrease in the BTE, OP, CO and total unburned hydrocarbons. Sayin and Canakci¹¹ experimentally studied the influence of IT on the engine performance and exhaust emissions of a single cylinder diesel engine using ethanol diesel blends with ethanol varying from 0 to 15%. They showed that with the advancement in IT (30° and 33° BTDC) emissions like HC and CO decrease whereas NOx and CO₂ increase. Silvio et al.¹² conducted tests in a naturally aspirated MWM 229 DI four-stroke 70 kW diesel generator fuelled with pure palm oil heated to 100°C. The results indicated that there is a decrease in SFC and an increase in EGT, CO, CO₂, HC and NOx emissions with the load. The SFC, EGT, CO, CO₂ and HC values are higher for palm oil than diesel except NOx, which has a lower value. Jindal et al.¹³ studied the effects of the engine design parameters, viz. CR and fuel IP on the performance parameters of the engine like BSFC, BTE and emissions parameters such as CO, CO₂, HC, NOx and OP when fuelled with jatropha methyl ester. It is found that the combined increase of CR and IP increases the BTE and decreases the BSFC and emissions. The optimum engine parameter combination is observed at CR 18 and IP 250 bar. Sayin¹⁴ experimentally investigated the performance and exhaust emissions of diesel engine fuelled with methanol–diesel and ethanol–diesel blends. The BSFC, emissions of nitrogen oxides, BTE, OP and emissions of CO increase with methanol–diesel and ethanol–diesel blends. However, total hydrocarbon emissions are found to decrease with methanol–diesel and ethanol–diesel blends. Ramdhas et al.¹⁵ reported an increase in the BTE and decrease in the fuel consumption for lower blends of rubber seed oil biodiesel. However, exhaust gas emissions were found to decrease with a raise of biodiesel concentration. Celik¹⁶ showed that the engine power is increased by 29% with 50% of ethanol – 50% gasoline fuel when compared with 100% gasoline. The specific fuel consumption, CO, CO₂, HC and NOx emissions are reduced for ethanol–gasoline blend when compared to gasoline fuel. Behera and Murugan¹⁷ conducted experiments to study the combustion, performance and emission characteristics of a diesel engine fuelled with used transformer oil (UTO). The results showed an increase in thermal efficiency with significant improvement in reduction of smoke for UTO and its diesel blends as compared to diesel. But NOx emissions are higher for UTO and its diesel blends than for diesel. Puhan et al.¹⁸ investigated high linolenic linseed oil methyl ester fuelled in a constant speed, DI diesel engine with varied fuel IPs of 200, 220 and 240 bar. Pressure of 240 bar was found experimentally to be the optimum IP from emissions as well as performance perspective. CO, unburnt HCs and smoke emissions decrease and NOx emissions increase at optimum pressure. Gopal Gupta et al.¹⁹ conducted experiments on a sports utility vehicle to find the particulate emissions in karanja biodiesel blends (KB20 and KB40). They conclude that the particulate emissions for karanja biodiesels are high when compared to those with standard mineral diesel. Chokri et al.²⁰ used waste vegetable oil methyl esters in diesel engines and found a decrease of 5% in power and 2% in NOx emissions for every 10% rise in the blend. The specific fuel consumption of biodiesel blends was found to be slightly high when compared with diesel. Mistri et al.²¹ performed endoscopic analysis for jatropha and karanja biodiesel and found that the ignition delay for biodiesels is short when compared with biodiesels. The results indicated that for diesel, cylinder pressures and premixed heat release rates are higher than for biodiesel. The tests also indicate that BSFC and soot formation increase while NOx levels decrease with retarded injections for all test fuels. Mani et al.²² studied the performance, emission and combustion characteristics of DI diesel engine fuelled with waste plastic oil and reported that performance of the engine is the same when fuelled with waste plastic oil. The carbon dioxide, unburned HC and CO are marginally higher than that of the diesel but smoke reduced by about 40–50%. Mani and Nagarajan²³ studied the influence of IT on performance, emission and combustion characteristics of a DI diesel engine running on waste plastic oil. They report that at the retarded IT of 14° BTDC, NOx, CO and HC decrease while BTE, CO₂ and smoke emissions increase under all the test conditions. In the works of Lee et al.²⁴ waste plastic is converted into oil by using pyrolysis. Experiments are conducted on a single cylinder diesel engine to find the performance of the engine running with waste plastic oil and its diesel blends. They report that torque, cylinder pressures and net heat release rates decrease with the increase of plastic oil content in the blend. Kaimal and Vijayabalan²⁵ added DEE additives to plastic oil and reported that there is a rise in BTE of the blends with DEE addition. It is also mentioned in the work that with use of DEE there is a significant reduction in BSFC, smoke and NOx. They also noted a slight improvement in CO emissions and higher HC emission with DEE-blended plastic oil. Senthilkumar and Sankaranarayanan²⁶ blended jatropha methyl esters with waste plastic oil and compared the results with pure plastic oil. They found that BTE is more for blend of PJ 20 when compared with pure plastic oil. Also it is identified that BSFC increases and CO, HC and smoke emissions decrease with increase of jatropha methyl esters content. The heat release rates are found to be higher for pure plastic oil when compared with all other JME blends. Sehmus²⁷ studied the emissions from diesel generator fuelled with waste cooking sunflower oil and two fossil diesel fuels. They reported that OP is low for both the fuels and nitric oxide (NO) emissions are higher for both fuels. Fuel consumption and HC emissions are more for biodiesel compared with both fossil diesels. Amin and Alireza²⁸ studied the effects of biodiesel on the performance of a diesel power generator and reported that for all biodiesel–diesel blends, brake power, brake torque and brake thermal efficiency are higher whereas BSFC is lower at high engine loads.

From the above literature review, it is observed that a lot of research has been carried on biodiesels and their blends, but very few papers on plastic oils are noticed in the literature. It is also observed that plastic oils are blended with diesel to improve their performance and emission characteristics. The effect of IT on plastic oil was studied by considering only standard and retarded ITs.²³ The present work is an endeavour to study the effect of ITs, IP and CR on the performance, emissions and combustion characteristics of plastic oils blended with diesel and ethanol.

Experimental set-up and procedure

The schematic layout of a single cylinder, DI, four-stroke VCR engines is shown in Figure 1.

Figure 1.

Schematic layout of the engine test set-up. DAQ: Data Aquisition; ECU: Electronic control unit.

The specifications of the engine are shown in Table 1. The set-up includes necessary instruments for online measurement of cylinder pressure, IP and crank angle (CA). A piezo sensor is mounted on engine head through the sleeve and another mounted on fuel line near injector. IT kit is provided for varying the IPs and ITs.

Table 1.

Engine specification.

Engine model	Kirloskar, TV1
Engine details	Four stroke, compression ignition, constant speed, vertical, water cooled, computerized diesel engine
No. of cylinders	One
Bore	87.5 mm
Stroke	110 mm
Swept volume	661 cc
Compression ratio	12:1–18:1
Rated output	5.2 kW at 1500 r/min

The output shaft of the eddy current dynamometer is fixed to a strain gauge-type load cell for measuring applied load on the engine. The set-up has transmitters for air and fuel flow measurement. Provision is also made for online measurement of the temperature of the exhaust gas, cooling water and calorimeter water inlet and outlet. Windows-based engine performance analysis software package ‘Engine Soft V8’ is used for online performance evaluation. Experiments are conducted for different test fuels like P100 (pure plastic oil), P90D10 (90% plastic oil, 10% diesel), P90D5E5 (90% plastic oil, 5% diesel, 5% ethanol), P80D10E10 (80% plastic oil, 10% diesel, 10% ethanol) and pure diesel. The properties of prepared plastic oil blends are tested in the laboratory using standard test procedures and are listed in Table 2. Experiments were carried out at different operating conditions of the engine such as CRs 17 and 18; IPs 220, 240 and 260 bar; ITs 15°, 18° and 21° BTDC to find performance, emission and combustion characteristics of the engine. The emission and smoke tests are conducted by using five gas analyser and smoke meter, respectively.

Table 2.

Properties of test samples.

Properties	Diesel	P100	P90D10	P90D5E5	P80D10E10
Calorific value (kJ/kg)	44,798	45,187	40,040	40,208	39,664
Moisture (%)	–	0.21	0.16	0.13	0.08
Sulphur (%)	–	0.12	1.20	1.39	1.14
Flash point (°C)	>52	<28	146	141	129
Pour point (°C)	−40	24	10	11	8
Total sediments (%)	–	0.087	0.022	0.026	0.08
Viscosity (cSt)	1.9	2.59	2.90	2.58	2.66
Density (kg/m³)	832	801.3	808	802	804
Ash content (%)	–	Nil	0.002	0.001	0.002
Carbon residue (%)	–	–	0.66	0.55	0.49

The measurement range and accuracy of five gas analyser and smoke meter are given in Table 3. The uncertainties accompanied with experimental parameters are analysed and presented in Table 4.

Table 3.

Five gas analyser and smoke meter specifications.

S. no.	Instrument	Measurement	Range	Resolution	Accuracy
1.	Five gas analyser	CO	0–15%	0.001%	±0.006%
		HC	0–30,000 ppm	1 ppm	±12 ppm
		NOx	0–5000 ppm	1 ppm	±20 ppm
		CO₂	0–20%	0.01%	±0.5%
		O₂	0–25%	0.01%	±0.1%
2.	Smoke meter	HSU	0–99.9	0.1%	±0.1%
2.	Smoke meter	K	0–α	0.01 m⁻¹	±0.1 m⁻¹

CO: carbon monoxide; HC: hydrocarbon; HSU: Hatridge smoke unit ; NOx: oxides of nitrogen.

Table 4.

Uncertainty analysis.

Measured parameters	Percentage uncertainty
Engine speed	±0.5
Temperature	±0.5
CO	±0.7
HC	±3.0
Oxides of nitrogen	±0.1
Crank angle encoder	±0.2
Load	±0.5
Calculated parameters
Power	±2.1
Brake thermal efficiency	±3.4
Brake-specific fuel consumption	±4.3

CO: carbon monoxide; HC: hydrocarbon.

Results and discussion

An overall observation of the results indicates that the addition of diesel and ethanol to the plastic oil gives higher BTE. A consolidated view of the results is presented in Table 5. It can also be observed from Table 5 that the fuel P80D10E10 gives low CO and HC emissions whereas P90D5E5 gives low smoke and BSFC compared to diesel. The results presented in this table are obtained at CR18, IT 21° and IP 260 bar. A more detailed discussion on the effect of the above system parameters on BTE, BSFC and various emissions is presented below.

Table 5.

Consolidated results at CR 18, IP 260 bar and IT 21° BTDC.

Engine parameters	D100	P90D5E5	P80D10E10	P100
BTE (%)	30.9	35.9	31.8	26
BSFC (kg/kW h)	0.3	0.19	0.26	0.31
CO (%)	0.129	0.098	0.085	0.205
HC (ppm)	5	3	2	7
Smoke (%)	81.12	68.05	76.52	87.25
NOx (ppm)	386	423	439	405

BSFC: brake-specific fuel consumption; BTE: brake thermal efficiency; CO: carbon monoxide; HC: hydrocarbon; NOx: oxides of nitrogen.

BTE

BTE plays a vital role in evaluating the performance of the engine. Figure 2 shows the variation of BTE with ITs and IPs at two different CRs and at maximum load. The results show that at any CR and any IP the brake thermal efficiencies of all the blends increase with an increase of ITs. Advancing the IT towards TDC decreases the BTE due to incomplete combustion. When the advance in IT was changed from natural injection 21° to 15°, BTE reduced by 14, 14 and 16% for P90D5E5, diesel and plastic oil, respectively. BTE increased with an increase of IPs for all the blends. This is because of the fact that at higher IP better atomization is observed which results in enhanced efficiency. Highest BTE is observed for the blend P90D5E5 at pressure of 260 bar. BTE also increased with increase in CR for all the blends. This is due to the decrease in ignition delay with the increase in CR resulting in better efficiency. The increase in CR also increases the in-cylinder temperatures which enhance the combustion and thermal efficiency. The BTE is increased by 15% for P90D5E5 with an increase of CR from 17 to 18 at 260 IP and 21° IT. The blends P90D5E5, P90D10, P80D10E10, D100 and P100 exhibit a decreasing order of efficiency.

Figure 2.

Variation of BTE with ITs and IPs at CRs of 17 and 18. BTDC: before top dead centre; CR: compression ratio; IP: injection pressure; IT: injection timing.

BSFC

The effect of different plastic oil blends and IT on the BSFC is shown in Figure 3.

Figure 3.

Variation of BSFC with ITs and IPs at CRs 17 and 18. BTDC: before top dead centre; CR: compression ratio; IP: injection pressure; IT: injection timing.

The experimental observations are considered at maximum load and constant speeds but for varying IPs and ITs. From Figure 3 it is noticed that with increase of IT, the BSFC of all the blends decreased. BSFC increased by 42, 25, 24% for P90D5E5, D100 and P100, respectively, when the IT is advanced by 6° towards TDC. There was a decrease in specific fuel consumption for the plastic oil ethanol blends when compared with diesel. It is also seen from Figure 3 that as the IP increases there is a reduction in fuel consumption for all the blends. The increase in IP decreases the fuel droplet size resulting in better vaporization and mixing of the fuel. As the CR increased, BSFC decreased for all the blends.

EGTs

Figure 4 shows the variation of EGT with different ITs, different IPs and at CR 17 as well as 18. It is evident from Figure 4 that EGT increases with retarding ITs and also with increase of IPs for all the blends. The retarded ITs increase the time available for the air and fuel to mix well resulting in better combustion of the fuel, thus results in high EGTs. The increase in EGTs with IP can also be attributed to the better atomization of the fuel at higher pressures enhancing the combustion. It is also observed from Figure 4 that the EGTs are increasing with increase in CR. This is due to the increase of temperatures and pressures with CR.

Figure 4.

Variation of EGTs with ITs and IPs at CRs of 17 and 18. BTDC: before top dead centre; CR: compression ratio; IP: injection pressure; IT: injection timing.

The EGTs are found to be increasing with increase in ethanol content in the blend. The high oxygen content of ethanol in the blend might be responsible for possible enhancement in combustion resulting in higher gas temperatures. The EGTs for the blends recorded in descending order are P80D10E10, P90D5E5, P100, D100 and P90D10.

HC emissions

Unburnt HC emissions are because of the incomplete combustion of the fuel. Typically, unburnt HCs are a serious problem with light loads in compression ignition engines. The influence of different blends on unburnt HC emission is shown in Figure 5.

Figure 5.

Variation of HC emissions with ITs and IPs at CRs of 17 and 18. BTDC: before top dead centre; CR: compression ratio; IP: injection pressure; IT: injection timing.

HC emissions are reduced by 20, 31, 26.3, 16.7 and 7% for the blends P80D10E10, P90D5E5, P90D10, D100 and P100, respectively, at an IT of 21° and IP of 260 bar with the retardation of IT from TDC. It is also noticed that HC emissions are increased for all the blends with advancement in injection. This is due to the increase in ignition delay by advancing the injection towards TDC. It is evident that as the percentage of ethanol content in the blend increases, the quantity of HC emissions reduced. This is because of the increase of oxygen content with ethanol blend. HC emissions decrease with the increase of IPs for all the blends because of the better atomization in the combustion chamber. HC emissions are also found to decrease with increase of CR which may be because of the rise in temperature and pressures resulting in better combustion. HC emissions are reduced by 66 and 58% for the blend P80D10E10 when compared with diesel and pure plastic oil at CR 18, IT of 21° BTDC and IP of 260 bar. The least HC emissions are observed for the blend P80D10E10.

CO emission

The variation of CO emissions for different blends of plastic oil with different CRs, IPs and ITs is shown in Figure 6. The CO emissions are found to decrease for all the blends with retarded injection from TDC. This is because of the time available for mixing of fuel and air. CO emissions are reduced by 11, 9, 7.6, 17.6 and 4.5% for the blends P80D10E10, P90D5E5, P90D10, P100 and D100, respectively, when the IT is 21° BTDC. CO emissions are also found to reduce for all the blends with the increase of CRs and IPs due to the high temperatures inside the combustion chamber. The CO emissions are reduced by 42 and 61% for the blend P80D10E10 when compared with diesel and pure plastic oil respectively at IT 21° BTDC, IP 260 bar and CR18.

Figure 6.

Variation of CO emissions with effect of ITs and IPs at CRs 17 and 18. BTDC: before top dead centre; CR: compression ratio; IP: injection pressure; IT: injection timing.

NOx emissions

NOx emissions are a result of the non-equilibrium chemical reaction between oxygen and nitrogen molecules in the high temperature burnt gas regions. The NOx in the tailpipe emissions contain mainly nitrogen dioxide and NO. The formation of NOx is highly dependent on the in-cylinder temperatures and the oxygen concentration in the cylinder. Figure 7 shows the variations of NOx emissions for various ITs, IPs and CRs. It is seen from the figure that NOx emissions for different blends increase with retarding ITs and with increase in IPs. This is because the retarded ITs result in higher temperatures.

Figure 7.

Variation of NOx emissions with ITs and IPs at CRs 17 and 18. BTDC: before top dead centre; CR: compression ratio; IP: injection pressure; IT: injection timing.

The NOx emissions are found to be the lowest for P90D10 due to low in-gas temperatures. The NOx concentrations increase with increase of IPs because of better atomization resulting in high temperatures.

The emissions of NOx increase with increase of CR. It is found that for P90D5E5 NOx emissions increased by 13.6 and 10.3% when compared with diesel and pure plastic oil, respectively, at IT 21° BTDC, IP 260 bar and CR 18. From Figure 4 it is also evident that the exhaust gas temperatures are increasing with IT indicating a clear relation between gas temperatures and NOx emissions.

Smoke

Variation of smoke with IT, IP and CR for all the test fuels is shown in Figure 8. Smoke emissions depend mainly on the local and global air–fuel ratios and fuel spray characteristics. From Figure 8 it is clear that P90D5E5 shows less smoke emission when compared with the remaining blends at all pressures and CRs. The smoke emissions for P90D5E5, P90D10, P80D10E10, D100 and P100 decrease by 12, 14, 14, 13 and 7%, respectively, at CR of 18 and IP of 260 bar by retarding the IT from 15° to 21° BTDC.

Figure 8.

Variation of smoke with ITs and IPs at CRs 17 and 18. BTDC: before top dead centre; CR: compression ratio; IP: injection pressure; IT: injection timing.

Smoke emissions are found to decrease for all the blends with increase of IPs and CRs. Smoke decreases for all the blends because of the increase in temperatures with compression. Smoke is found to be least for P90D5E5 which reduced by 11 and 18% when compared with diesel and pure plastic oil, respectively, at IT 21° BTDC, IP 260 bar and CR 18.

Cylinder pressure

The effect of CA on cylinder pressure at full load is shown in Figure 9 which portrays the cylinder pressures of all the test fuels at CR 18, IT 21° BTDC and IP of 260 bar.

Figure 9.

Cylinder pressure variation with CA. CR: compression ratio; IP: injection pressure; IT: injection timing.

It is observed that P90D5E5 has highest cylinder pressure followed by P80D10E10, D100, P90D10 and P100. The low values of cylinder pressures of the blend are due to low gas temperatures inside the cylinder. All the fuels have their peak cylinder pressures after TDC. The smooth curves in the pressure CA diagram depict a smooth combustion for all the test fuels inside the combustion chamber.

Net heat release rate

The net heat release rates of plastic oil and its ethanol blends are shown in Figure 10. Net heat release rates can be obtained by applying the first law of thermodynamics to the engine assuming it to be a closed system.

Figure 10.

Net heat release rate variation with CA. CR: compression ratio; IP: injection pressure; IT: injection timing.

The net heat release rate is expressed as

\frac{d Q}{d θ} = \frac{γ}{γ - 1} P \frac{d V}{d θ} + \frac{1}{γ - 1} V \frac{d P}{d θ}

where γ is the polytropic index, Q is Net heat release, θ is the CA and V and P are instantaneous volume and pressure inside the cylinder. From the figure, it is seen that the net heat release rate is more for P100 than for the remaining blends at the same operating conditions because of its high calorific value. The negative values during the initial stages of combustion indicate the absorption of heat of air by the atomized fuel to start combustion. From Figure 10 it is evident that maximum amount of energy is released only after TDC for all the tested fuels. Blends P90D5E5, P80D10E10, P90D10 and D100 follow a descending order of heat release as shown in Figure 10.

Mass fraction of fuel burned

Figure 11 shows the variation of the mass fraction of fuel burned with respect to CA at IT 21⁰ BTDC, IP 260 bar and at CR 18 which gives the detailed information about the start of combustion and end of combustion. It is found that pure plastic oil has highest burning rate when compared with other blends used. With the increase of ethanol content, the burning rate also tends to increase because of the faster burning characteristics of ethanol. The combustion duration decreased with an increase of ethanol content in the blend, which is due to the fact that high volatility of ethanol results in wider diffusive flames and quick combustion.

Figure 11.

Variation of mass fraction of fuel burnt with CA. CR: compression ratio; IP: injection pressure; IT: injection timing.

Rate of pressure rise

Figure 12 represents the rate of pressure rise of different blends with respect to the CA at injection 21° BTDC, IP 260 bar and CR 18. From Figure 12 it is evident that P90D5E5 has lowest rate of pressure rise when compared with other blends. The rate of pressure rise is delayed for the blends such as P90D5E5, P80D10E10 and P100.

Figure 12.

Variation of rate of pressure rise with CA. CR: compression ratio; IP: injection pressure; IT: injection timing.

The present results are compared with available results in literature as shown in Table 6 and are found to be in accordance with the literature.

Table 6.

Validation of experimental data.

S. no.	Engine parameters	Engine conditions
		Kaimal and Vijayabalan²⁵	Senthilkumar and Sankaranarayanan²⁶	Present study
		IT 23° BTDC, IP 200 bar at CR 17	IT 23° BTDC, IP 200 bar at CR 18	IT 21° BTDC, IP 220 bar
1	BTE	27.28	22.5	28 @ CR 17
2	CO	1.25 (g/kW h) ≈ 0.034%	0.25%	0.32% @ CR 18
3	NOx	6.9 (g/kW h) ≈ 1039 ppm	650 ppm	349 ppm @ CR 18
4	HC	0.14 (g/kW h) ≈ 69 ppm	47 ppm	11 ppm @ CR 18

BTDC: before top dead centre; BTE: brake thermal efficiency; CO: carbon monoxide; CR: compression ratio; HC: hydrocarbon; IP: injection pressure; IT: injection timing; NOx: oxides of nitrogen.

Conclusions

The following salient conclusions can be made from the present experimental study.

The P90D5E5 blend has the highest BTE of 36% at CR 18, IT 21° BTDC and IP 260 bar. This is more than the BTE of diesel and pure plastic oils by 16 and 38%, respectively.

BSFC is found to decrease for plastic oil ethanol blends when compared with diesel. Plastic oil blended with diesel and ethanol has low CO, HC and smoke than diesel. However, NOx emissions are higher for plastic oil ethanol blends.

Combustion characteristics like cylinder pressures and rate of pressure rise are more for P90D5E5. The mass fraction of fuel burnt and net heat release rates are more for pure plastic oil when compared with other blends.

It is also observed that by increasing CR, IP and retarding the injection from TDC there is an increase in BTE and NOx whereas BSFC, CO, HC and smoke are decreasing.

Footnotes

Acknowledgements

The authors would like to thank Professor D. Varada Raju for his guidance throughout the preparation of this paper.

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: The authors thank AICTE, New Delhi for providing the funding under RPS (Research promotion scheme) to carry out this work.

B Govinda Rao has obtained his doctorate from Jawaharlal Nehru Technological University, Hyderabad. In his vast teaching experience of 18 years, he has published research articles in National and International Journals. His research interests are in the fields of Heat Transfer, Alternative fuels and IC engine technologies.

Y Datta Bharadwaz is currently working as an Assistant Professor in department of mechanical engineering, GVP College of Engineering (A), Visakhapatnam, India. His research interests are in the fields of Heat transfer, Evolutionary Computation, Alternative fuels and IC engine technologies.

Chukka Virajitha is a post graduate student in GVP College of Engineering (A), Visakhapatnam, India.

V Dharma Rao is working as a professor in GVP College of Engineering(A), Visakhapatnam, India after retirement from Andhra University, Visakhapatnam, India. He guided 10 doctoral degrees and published 49 research papers in refereed international journals. Professor Dharma Rao also acted as a technical consultant for many reputed firms.

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Effect of injection parameters on the performance and emission characteristics of a variable compression ratio diesel engine with plastic oil blends – An experimental study

Abstract

Keywords

Introduction

Experimental set-up and procedure

Results and discussion

BTE

BSFC

EGTs

HC emissions

CO emission

NOx emissions

Smoke

Cylinder pressure

Net heat release rate

Mass fraction of fuel burned

Rate of pressure rise

Conclusions

Footnotes

Acknowledgements

Declaration of conflicting interests

Funding

References