Environmental Science and Pollution Research https://doi.org/10.1007/s11356-017-1070-3

RESEARCH ARTICLE

Effect of injection pressure on performance, emission, and combustion characteristics of diesel–acetylene-fuelled single cylinder stationary CI engine Anmesh Kumar Srivastava 1 & Shyam Lal Soni 1 & Dilip Sharma 1 & Narayan Lal Jain 1 Received: 11 September 2017 / Accepted: 18 December 2017 # Springer-Verlag GmbH Germany, part of Springer Nature 2017

Abstract In this paper, the effect of injection pressure on the performance, emission, and combustion characteristics of a diesel-acetylene fuelled single cylinder, four-stroke, direct injection (DI) diesel engine with a rated power of 3.5 kW at a rated speed of 1500 rpm was studied. Experiments were performed in dual-fuel mode at four different injection pressures of 180, 190, 200, and 210 bar with a flow rate of 120 LPH of acetylene and results were compared with that of baseline diesel operation. Experimental results showed that highest brake thermal efficiency of 27.57% was achieved at injection pressure of 200 bar for diesel-acetylene dualfuel mode which was much higher than 23.32% obtained for baseline diesel. Carbon monoxide, hydrocarbon, and smoke emissions were also measured and found to be lower, while the NOx emissions were higher at 200 bar in dual fuel mode as compared to those in other injection pressures in dual fuel mode and also for baseline diesel mode. Peak cylinder pressure, net heat release rate, and rate of pressure rise were also calculated and were higher at 200 bar injection pressure in dual fuel mode. Keywords Diesel engine . Acetylene . Injection pressure . Dual fuel

Nomenclature aTDC After top dead center BTE Brake thermal efficiency (%) BSEC Brake-specific energy consumption (kJ/kWh) bTDC Before top dead center CI Compression ignition CO Carbon monoxide CO2 Carbon dioxide CR Compression ratio CV Calorific value (kJ/kg) DAD Data acquisition device DF Dual fuel DI Direct injection EGT Exhaust gas temperature (°C) HC Hydrocarbon IC Internal combustion Responsible editor: Philippe Garrigues * Anmesh Kumar Srivastava [email protected] 1

Mechanical Engineering Department, Malaviya National Institute of Technology Jaipur, J.L.N Marg, Jaipur, Rajasthan, India

IP IT LPH N NHRR NOx PCP RPR TDC VCR

Injection pressure (bar) Injection timing (0) Liters per hour RPM Net heat release rate (J/0CA) Oxides of nitrogen Peak cylinder pressure (bar) Rate of pressure rise (bar/0CA) Top dead center Variable compression ratio

Introduction Use of alternate fuels is found to be an attractive solution for easing the difficulty of meeting the increased demand for energy and depleting oil reserves, and at the same time, their use help in reduction of pollutant emissions (Wei and Geng 2016). Among the biofuels, biodiesel, and bioalcohols are the promising alternatives and can be used as future alternative transport fuels. There are few limitations regarding their utilization in diesel engines like high viscosity and poor atomization, but research is on for improving their quality and performance coupled with limiting environmental pollution (Imdadul

Environ Sci Pollut Res

et al. 2017). Many other alternate fuels such as natural gas, liquefied petroleum gas, biogas, hydrogen, ethanol, and methanol have been under research for compression ignition and spark ignition engines and have given encouraging results. Likewise, acetylene gas also has great potential to go about as future alternate fuel. Acetylene is a colorless gas having garlic-like smell. Production of acetylene involves following reaction when produced with calcium carbide as shown in following Eqs. (1) and (2), respectively (Price 2006). CaCO3 þ C ðgraphiteÞ→CaC2

ð1Þ

CaC2 þ H2 O→Ca ðOHÞ2 þ C2 H2

ð2Þ

Other methods for production of acetylene includes partial combustion of methane with oxygen or thermal cracking of hydrocarbons. Acetylene has a wide flammability range, high flame speed, and hence, promotes faster energy release. Acetylene can be a viable alternative to conventional fuels obtained from petroleum which is often manufactured from coal, limestone, and water (non-petroleum) (Hilden and Stebar 1979). Acetylene with its remarkable properties such as wide flammability range and high flame speed appears to be a viable alternate fuel for IC engines if it is utilized properly (Lakshmanan and Nagarajan 2011). Table 1 shows the comparison of physical and combustion properties of acetylene, hydrogen, and diesel. NOx, HC, and CO emissions were found to reduce while using acetylene in dual fuel mode (Wulff et al. 2001). Lakshmanan and Nagarajan (2009) reported lower brake thermal efficiency (BTE) and suggested that thermal efficiency can be improved with reduced NOx emissions by applying techniques such as timed manifold injection (TMI) and timed port injection (TPI) on using acetylene in dual-fuel mode. NOx, CO, and HC emissions reduced along with an increment in smoke level compared to diesel mode on using TMI technique with acetylene in dual-fuel mode (Lakshmanan and Nagarajan 2010a). Acetylene when used with diesel and used-transformer oil (UTO) in dual-fuel mode gave lower smoke and exhaust gas temperature (EGT) while NOx level was higher compared to neat diesel or neat UTO Table 1 Properties of acetylene compared with other fuels (Lakshmanan and Nagarajan 2010b) Properties

Acetylene Hydrogen Diesel

Formula

C2H2 1.092 305 13.2 2.5–81 0.3–9.6 48,225 50,636

Density kg/m3 (At 1 atm and 20 °C) Auto ignition temperature (°C) Stoichiometric air fuel ratio (kg/kg) Flammability limits (volume %) Flammability limits (equivalent ratio) Lower calorific value (kJ/kg) Lower calorific value (kJ/m3)

H2 0.08 572 34.3 4–74.5 0.1–6.9 1,20,000 9600

C8–C20 840 257 14.5 0.6–5.5 – 42,500 –

operation (Behera et al. 2014). Acetylene with diethyl ether in homogeneous charge compression ignition (HCCI) mode gave low smoke and NOx emissions while HC and CO were more than conventional diesel mode (Sudheesh and Mallikarjuna 2013). Lakshmanan and Nagarajan (2010b) also reported low thermal efficiency, smoke, HC, and CO emissions and a rise in NOx emission and peak pressure during acetylene aspiration. In diesel engine, fuel injection pressure affects the performance and emissions and is one of the major operating parameters (Jindal et al. 2010). High injection pressure (IP) improves the performance and reduces emissions (Sastry et al. 2015). Aalam et al. (2016) studied the effect of mahua methyl ester blend at varying IP from 22 to 88 MPa where high BTE and improved combustion characteristics were observed at highest IP of 88 MPa compared to other IP. There was a gradual fall in smoke, CO, and HC emission with increase in IP. Quadri et al. (2015) conducted experiment with hydrogen in dual fuel mode along with diesel at different IPs of 200, 220, and 240 bar and observed that on using 20% hydrogen with diesel, highest BTE, and NOx emission along with lowest unburnt hydrocarbon (UHC) and CO emission were obtained at 220 bar. Liu et al. (2015) investigated the effect of IP on performance and exhaust emissions using diesel/methanol dual fuel (DMDF) combustion mode. As IP increased, the maximum cylinder pressure and the peak heat release rate increased while brake specific fuel consumption (BSFC), CO, HC, and smoke emissions decreased and NOx emission increased in DMDF mode. Gumus et al. (2012) studied the effect of IP using biodiesel–diesel blends at different IP of 18, 20, 22, and 24 MPa. Increased IP resulted in decreased BSFC for high percentage of biodiesel–diesel blends. Decrease in smoke, CO and UHC while increase in CO2, O2, and NOx with increased injection pressure were observed. Ryu (2013) studied effects of pilot IP in biodiesel and compressed natural gas (CNG) dual fuel combustion (DFC) system. The combustion stability of biodiesel and CNG DFC mode increased with increase of pilot IP while smoke decreased and NOx emissions increased on increasing pilot IP in biodiesel–CNG DFC system. Nanthagopal et al. (2016) studied the effect of IP using Calophyllum inophyllum methyl ester at IPs of 200, 220, and 240 bar in 100% biodiesel fuelled DI diesel engine. At higher injection pressure there was a reduction in brake-specific energy consumption (BSEC) of Calophyllum inophyllum methyl ester. Also, reduction in emissions of UHC, CO, and smoke at 220 bar IP of biodiesel as compared to other IPs was reported. However, NOx emission increased with increase in IP of Calophyllum inophyllum methyl ester. Shehata et al. (2015) studied the effect of IPs using corn and soybean biodiesel blends at different IP of 180, 190, and 200 bar. Increased IP gave better BTE and BSFC compared to original IP, and best result was obtained at 200 bar IP. Sayin (2011) studied the effect of IP using methanol blended diesel fuel at different

Environ Sci Pollut Res

IP of 180, 200, and 220 bar. 200 bar IP gave the best results in terms of BSFC. It was suggested to use high IP for decreasing smoke, CO, and UHC emissions and low IP for decreasing NOx and CO2 emissions. The effect of IP while using orange skin powder diesel solution (OSPDS) at different IPs of 215, 235, and 255 bar was studied and it was found that at 235 bar the combustion, performance, and emissions of the engine operating on the test fuel were better than those at IPs (Purushothaman and Nagarajan 2009). Behera and Murugan (2013) concluded that at 230 bar fuel nozzle opening pressure UTO gave a better performance with lower emissions than those at 200 bar while using used transformer oil (UTO). Channapattana et al. (2015) investigated the effect of the blends of honne biodiesel and diesel at different fuel IPs of 180, 210, and 240 bar. At 240 bar, higher BTE and lower BSFC were obtained compared to that at other IP for all blends. CO, HC, and smoke emissions at 240 bar were lower compared to those at other IPs while NOx emissions increased with increase in IP. Sastry et al. (2015) studied the effect of IP using isobutanol and ethanol as additives to the diesel-biodiesel blends at different IPs of 200, 225, 250, and 275 bar. BTE and fuel economy improved and reduction in CO and smoke were reported on increasing IP up to 250 bar. However, NOx emissions decreased marginally in some blends. Syed et al. (2017) studied the influence of injection opening pressure (IOP) for 20% blend (B20) of mahua oil methyl ester (MOME) and 22.5 liters per minute of hydrogen dual fuel mode at four different IOPs of 200, 225, 250, and 275 bar. At IOP of 250 bar maximum BTE, minimum BSFC, and lowest HC, CO and smoke emissions with increased concentration of NO x were obtained for B20-hydrogen dual fuel mode. Anbarasu and Karthikeyan (2015) investigated the effect of IP at 200, 220, and 240 bar on the canola biodiesel

Fig. 1 Schematic diagram of experimental setup

emulsion blend and found an improvement in BTE of 28.8% at 240 bar along with reduction in NOx emission at 200 bar using emulsified fuel. Balusamy and Marappan (2010) studied the effect of IP and injection timing using methyl ester of Thevetia peruviana seed oil in diesel engine. On increasing the IP and advancing, the injection timing BTE increased while there was reduction in CO, HC, and smoke emissions. Belagur and Chitimini (2010) investigated the effect of a blend of 50% honne oil with 50% diesel fuel (H50) at different injector opening pressures (200, 220, 240, and 260 bar). It was found that with H50, on increasing injector, opening pressures BTE and NOx increased while CO, HC and smoke emissions reduced. 240 bar was found to be the best injector opening pressure for H50. Sayin et al. (2012) conducted experiment using canola oil methyl esters (COME) blended with diesel fuel for four different IPs of 18, 20, 22, and 24 MPa. The results showed that the high IP gave better results for BSFC, BSEC, and BTE compared to the original and low IPs.

Experimental setup and methodology The experimental setup for the present investigation is shown in Figs. 1 and 2. Tests were performed on a four-stroke, single cylinder, direct injection, 3.5 kW, variable compression ratio (VCR) diesel engine (Kirloskar make, India). Tables 2 and 3 illustrate the specifications of the engine and other instruments, respectively. The engine was connected to a water-cooled, eddy current dynamometer for loading. To vary the CR without stopping the engine, a tilting cylinder block arrangement was incorporated. The load was displayed digitally in kg through the load signal sent by the load sensor fitted with eddy current

Environ Sci Pollut Res

Fig. 2 Pictorial view of experimental setup

dynamometer. Flow of water was measured with the help of two rotameters provided for engine and calorimeter. Fuel line pressure and combustion pressure were measured by piezo type sensors mounted on the cylinder head and fuel injector. Optical crank-angle sensor delivered the signal for each degree rotation of crank shaft. Water and exhaust gas temperature were measured through thermocouples installed at

Table 2

Specifications of the diesel engine

Particular

Description

Type of engine

Research engine test setup—single cylinder, four-stroke, multi-fuel, VCR, computerized Apex Innovation 240PE (with modified Kirloskar TV1 engine) 0.0875 m 0.110 m 0.000661 m3 0.234 m 3.5 kW at 1500 rpm Water cooled 18:1 to 22:1 0–250 bTDC Hemispherical bowl in piston type Engine cooling 40–400 LPH; calorimeter 25–250 LPH 15 l, dual compartment, glass fuel metering pipe Eddy current, water cooled 0.185 m

Make and model Bore Stroke Cubic capacity Connecting rod length Max. power Type of cooling CR range Injection variation Combustion chamber Rotameters Fuel tank Dynamometer Dynamometer arm length Air box Orifice diameter Engine performance analysis software

Mild steel fabricated with orifice meter and manometer (water filled) 0.020 m BEnginesoft^ supplied by Apex Innovation, India

different locations in the experimental setup. Fuel tank, air box, fuel measuring burette, and manometer were mounted on the panel box. Air flow rate, engine speed, various temperatures, cylinder, and fuel pressure variations were recorded by the National Instruments make data acquisition device (DAD). For performance analysis analog, signals from various locations of the setup were supplied to the BEnginesoft^ software. The engine was modified for dual fuel operation by connecting a hose pipe from an acetylene gas generator to the air intake manifold through a flame arrestor. The acetylene gas flow rate was measured using a calibrated gas flow meter. The acetylene gas was produced in a constant pressure acetylene gas generator. Calcium carbide and water were used as raw materials for the production of acetylene gas. The pressure of acetylene gas at the outlet of the generator was found to be constant at 1.10 bar. The emission analysis was carried out by using an AVL Digas 444 flue gas analyzer for measuring CO, HC, and NOx emissions while AVL DiSmoke 480 BT smoke meter was used for measuring smoke (opacity). Table 4 shows the resolution, accuracy, and range of these emission parameters. Cylinder pressure data obtained through DAD was used to draw P–θ curves, rate of heat release, and rate of pressure rise curves with respect to crank angle at different loads for different IP.

Experimental procedure The engine was first operated with neat diesel (baseline) at CR 20, IP of 210 bar, and injection timing (IT) of 230 before top dead center (bTDC) while for dual fuel mode, the optimum CR was 21; therefore, the readings in dual fuel mode were taken at the CR 21 and IT of 230 bTDC for different IPs. The engine was run at no load so as to warm up the engine. During experimentation, the engine was tested with 20, 40, 60, 80, and 100% load for

Environ Sci Pollut Res Table 3

Specifications of other instruments

Instrument

Make

Type/model

Resolution

Range

Gas flow meter

Apex Engineering

Acrylic Rotameter

–

60–600 LPH

Pressure sensors

PCB Piezotronics

Piezo type with low noise cable

–

Combustion: 350 bar, diesel line: 350 bar

Temperature sensors Thermocouple

– –

RTD PT100 K Type

– –

0–100 °C 0–1200 °C

Load sensor Crank angle sensor Data acquisition device Air flow transmitter

– Kubler National Instruments Wika

Strain gauge

– 10 – 1 mm

0–50 kg 5500 rpm

NI USB-6210 Pressure transmitter

different injection pressures of 180, 190, 200, and 210 bar with 3.5 kW as 100% load. A standard burette of 100 ml with 1 ml division mounted on the test rig and a digital stopwatch were used for the measuring diesel flow rate. The exhaust gas was allowed to flow through a probe to measure HC, CO, NOx, and smoke concentrations in the exhaust gas using the gas analyzer and smoke meter and readings were taken. The flow of acetylene was regulated with the help of valve attached to the gas generator and was fixed at 120 LPH. Acetylene flow rate was measured with the help of gas flow meter. The injection pressure of the injector was varied by tightening or loosening the adjusting screw of the injector and the injector pressure was determined by a fuel injector pressure tester.

Uncertainty analysis of the experimental data Uncertainties in the experimental readings can occur due to various factors such as experimental methods adopted, instruments utilized, calibration, environment, working conditions, and so on. In order to determine the accuracy of measurement, uncertainty analysis carried out. The accuracies of the measurements and the maximum uncertainties in the calculated results are given in Table 4. Table 4

16-bit, 250 kS/s (−) 250 mm WC

Results and discussion The present experimental investigation focuses on performance, emission, and combustion analysis of optimized injection pressure for dual fuel mode. For this, initially, the flow rate of acetylene was optimized. Hence, four different acetylene flow rates of 60, 120, 180, and 240 LPH were tested at optimized compression ratio of 20 for baseline diesel at 210 bar IP and 230 bTDC IT. The maximum brake thermal efficiency was obtained at 120 LPH flow rate of acetylene. The optimized compression ratio for dual fuel operation was 21 at 210 bar IP and 230 bTDC IT (Srivastava et al. 2017). Therefore, in the present experimental investigation, 120 LPH of acetylene was inducted in intake manifold with air for diesel-acetylene dual fuel mode at CR 21 and the results were obtained at all loading conditions for four different injection pressures of 180, 190, 200, and 210 bar at 230 bTDC IT.

Performance analysis Figure 3 shows the variation of BTE with load at different injection pressures. BTE increased with increase in load in all the cases. The BTE in case of dual fuel operation is higher than that with baseline diesel due to wide flammability limit

The accuracies of the measurements and the maximum uncertainties in the calculated results (Srivastava et al. 2017)

Instrument

Parameter

Measuring range

Resolution

Accuracy

CO (% vol)

0–10% vol

0.01% vol

< 0.6% vol: ±0.03% vol

≥ 0.6% vol: ± 5% of indicated value AVL Digas 444 HC (ppm) 0–20,000 ppm vol ≤ 2000:1 ppm vol, < 200 ppm vol: ± 10 ppm vol > 2000:10 ppm vol ≥ 200 ppm vol: ± 5% of indicated value 0–5000 ppm vol 1 ppm vol < 500 ppm vol:± 50 ppm vol NOx (ppm) ≥ 500 ppm vol: ± 10% of indicated value AVL DiSmoke 480 BT Smoke (%) 0–100% 0.10% – Calculated parameters BTE (%) – – – BSEC (kJ/kWh) – – –

Max. uncertainty (%)

± 2.6 ± 2.3 ± 2.1 ± 1.5 ± 0.5 ± 0.5

Environ Sci Pollut Res

Fig. 3 Variation of BTE at different IPs

Fig. 5 Variation of EGT at different IPs

and higher flame velocity of acetylene gas. BTE increased with increase in IP up to 200 bar, and then it decreased with increase in IP. The increase in BTE can be due to fine spray, better atomization of diesel, and better combustion at higher IP [33]. While on further increasing IP, BTE reduced which may be due to reduction in the size of fuel droplets that have lesser momentum which affects the fuel distribution in the air leading to incomplete combustion (Syed et al. 2017; Jaichandar and Annamalai 2013). The highest BTE of 27.57% was found at 200 IP in comparison to 26.34, 26.96, and 25.72% at 180, 190, and 210 bar, respectively, in dual fuel mode while the BTE of baseline diesel was 23.34%. Figure 4 shows the variation of BSEC with load at different injection pressures. The BSEC decreased with increase in load in all the cases. BSEC in case of dual-fuel mode was lower than that in diesel mode due to higher conversion of acetylene gas into work. BSEC decreased with increase in IP up to 200 bar because of better atomization, vaporization of the fuel and improved air-fuel mixing that led to better combustion (Jaichandar and Annamalai 2013). BSEC increased on further increasing IP up to 210 bar due to poor combustion. The highest BSEC was found in the case of baseline diesel. The EGT increased with increase in load for all the cases as shown in Fig. 5. The EGT in case of baseline diesel was higher compared to that in dual fuel mode at all IPs. The EGT in case of dual fuel mode was lower than diesel mode because of the

higher flame speed of acetylene and advancement in the heat release rate. Reduction in EGT in dual fuel mode could also be due to higher thermal conductivity of gases leading to higher losses and lower EGT. In dual fuel mode the EGT decreased with increase in IP up to 200 bar, which could be due to the sluggish combustion leading to higher EGT at lower IP (Belagur and Chitimini 2010). It can also happen due to the heterogeneous combustion because of the large droplet size distribution in combustion chamber at lower IP and as the IP increased the droplet size became finer resulting in better fuel air mixing and smooth combustion (Agarwal et al. 2013). EGT increased with further rise in IP at 210 bar due to poor combustion.

Figure 6 depicts the variation of CO emission with load at different IPs. The CO emission in dual fuel mode was found to be lower than diesel mode at high loads. Due to high pressure and temperature at higher loads, complete burning of fuel takes place which leads to low CO emission in contrast to higher emission at low loads in dual-fuel mode (Srivastava et al. 2017). The CO emission decreases with increase in IP up to 200 bar. Increasing the injection pressure leads to complete combustion due to better fuel air mixing and reduced CO emission (Gumus et al. 2012). At 210 bar, CO increases

Fig. 4 Variation of BSEC at different IPs

Fig. 6 Variation of CO at different IPs

Emission analysis

Environ Sci Pollut Res

Fig. 7 Variation of HC at different IPs

Fig. 9 Variation of smoke at different IPs

because of lack of fuel- air mixing and insufficient time for combustion (Quadri et al. 2015). HC emission in dual fuel mode decreased with increase in IP up to 200 bar as shown in Fig. 7. The fuel air mixing was more proper on increasing the injection pressure which caused low HC emissions at high injection pressure than that at low injection pressures (Gumus et al. 2012). HC emission increased with further rise in injection pressure (210 bar), which could be due to improper mixing of fuel and air and insufficient time for combustion. Figure 8 shows the variation of NOx emission with load at different IPs. NOx emission was higher in dual-fuel mode compared to that in diesel mode because in dualfuel mode, the combustion chamber temperature was higher than diesel due to higher calorific value of acetylene gas compared to that of diesel (Srivastava et al. 2017). NOx emission increased with increase in IP upto 200 bar. Increase in NOx emission could be due to rapid combustion, high in-cylinder gas temperature, and peak pressure attained with higher IP. Further increase of IP to 210 bar lowered the NOx emissions, which could be due to improper combustion resulting in lower in-cylinder temperatures when compared to IP of 200 bar (Syed et al. 2017). Figure 9 shows the variation of smoke emission with load at different injection pressures. Smoke emission in dual fuel mode was found decreasing with increase in injection pressure

upto 200 bar. The higher smoke emission at lower injection pressure could be due to the large droplet size leading to poor atomization, while at higher injection pressure, droplet size reduced resulting in better fuel-air mixing and complete combustion which led to lower smoke emission (Jaichandar and Annamalai 2013). On increasing injection pressure above 200 bar, smoke emission increased, which might be due to the fact that too high an IP leads to thermal cracking due to high temperature of the mixture.

Fig. 8 Variation of NOx at different IPs

Fig. 10 Variation of PCP at different IPs

Combustion analysis Figure 10 shows the variation of cylinder pressure with crank angle at full load for different injection pressures. The peak cylinder pressure (PCP) at 100% load in case of dual-fuel operation was found to be 80.44, 82.15, 83.99, and 81.41 bar for IP 180, 190, 200, and 210 bar, respectively, as compared to the PCP of 71.88 bar for baseline diesel. PCP in dual fuel mode increased with increase in IP up to 200 bar. The highest PCP of 83.99 bar was obtained at IP 200 bar in case of dual-fuel mode beyond which PCP decreased. The increase in peak pressure from 180 to 200 bar IP might be due to proper atomization, better air-fuel mixing, and combustion. Further increase in injection pressure to 210 bar lowered peak cylinder pressure, which could be due to longer delay

Environ Sci Pollut Res

Conclusions

Fig. 11 Variation of NHRR at different IPs

period because of improper mixing of fuel leading to improper combustion (Syed et al. 2017). The net heat release rate (NHRR) increased with increase in IP due to increase in cylinder pressure and combustion temperature as shown in Fig. 11. In case of dual-fuel mode at full load, the maximum NHRR was 62.01, 67.01, 68.45, and 54.57 J/0CA at 180, 190, 200, and 210 bar respectively. NHRR for baseline diesel was 40.81 J/0CA. The NHRR in case of dual-fuel mode was higher compared to that in diesel mode. Higher energy density of acetylene diesel air mixture resulted in higher NHRR when compared to baseline diesel operation (Srivastava et al. 2017). NHRR increased from 180 to 200 bar injection pressure due to improved premixed combustion phase which could be due to better atomization and improved air fuel mixing (Jaichandar and Annamalai 2013).On further increasing IP to 210 bar, NHRR decreased. Figure 12 illustrates the trends for the rate of pressure-rise (RPR) with the crank angle for dual fuel mode at different IP and also for baseline diesel. At full load, the maximum rate of pressure rise (bar/0CA) for dual fuel mode was found to be 7.05, 7.60, 7.71, and 7.30 for IPs of 180, 190, 200, and 210 bar, respectively, while for baseline diesel the maximum rate of pressure rise was 4.92 bar/0CA. The maximum rate of pressure rise in case of dual fuel mode increased consistently with increase in injection pressure up to 200 bar beyond which it decreased.

In this study, the effect of injection pressure on performance, exhaust emission, and combustion characteristics of a diesel engine were experimentally investigated when the engine was fueled with diesel–acetylene in dual fuel mode and the results were compared with those in baseline diesel mode. Based on the experimental results, the following conclusions were drawn: Brake thermal efficiency increased with increase in IP up to 200 bar beyond which it decreased. The highest BTE of 27.57% was found in dual fuel mode at 200 IP in comparison to BTE of 23.34% for baseline diesel. BSEC in dual fuel mode decreased with increase in IP up to 200 bar beyond which it increased with increase in IP. Lowest BSEC in dual fuel mode was obtained at 200 bar IP while the highest BSEC was in the case of baseline diesel. The EGT in dual fuel mode decreased with increase in IP up to 200 bar. The lowest EGT was found at 200 bar IP in dual fuel mode. The CO and HC emissions in dual fuel mode decreased with increase in IP up to 200 bar, and hence, minimum CO and HC emissions were obtained at 200 bar for dual fuel mode. NOx emission in dual fuel mode increased with increase in injection pressure up to 200 bar beyond which it decreased. Smoke in dual fuel mode was found decreasing with increase in IP up to 200 bar, and on further increment of IP, smoke increased. The highest peak cylinder pressure, heat release rate, and rate of pressure rise in dual fuel mode were observed at 200 bar and were higher than that for baseline diesel mode. Thus, from this experiment, 200 bar injection pressure was found optimum for diesel-acetylene dual fuel mode in terms of performance, exhaust emissions (CO, HC, and smoke), and combustion characteristics. However, there was an increase in NOx emissions at 200 bar in dual fuel mode. Acknowledgements The authors acknowledge the valuable help of Mr. Ramesh Chand Meena, Senior Technician, I.C. Engines Lab, MNIT Jaipur, during experimentations. The authors are grateful for support from Malaviya National Institute of Technology Jaipur (MNIT Jaipur), India. All the equipments, machinery, and consumables were provided/funded by MNIT Jaipur.

References

Fig. 12 Variation of RPR at different IPs

Aalam CS, Saravanan CG, Anand BP (2016) Impact of high fuel injection pressure on the characteristics of CRDI diesel engine powered by mahua methyl ester blend. Appl Therm Eng 106:702–711. https://doi.org/10.1016/j.applthermaleng.2016.05.176 Agarwal AK, Srivastava DK, Dhar A, Maurya RK, Shukla PC, Singh AP (2013) Effect of fuel injection timing and pressure on combustion, emissions and performance characteristics of a single cylinder diesel engine. Fuel 111:374–383. https://doi.org/10. 1016/j.fuel.2013.03.016

Environ Sci Pollut Res Anbarasu A, Karthikeyan A (2015) Effect of injection pressure on the performance and emission characteristics of CI engine using canola emulsion fuel. Int J Ambient Energy 7269(3):1–6. https://doi.org/10. 1080/01430750.2015.1092472 Balusamy T, Marappan R (2010) Effect of injection time and injection pressure on CI engine fuelled with methyl ester of Thevetia Peruviana seed oil. Int J Green Energy 7(4):397–409. https://doi. org/10.1080/15435075.2010.493811 Behera P, Murugan S (2013) Studies on a diesel engine fueled with used transformer oil at different fuel injection nozzle opening pressures. Int J Ambient Energy 34(1):53–59. https://doi.org/10.1080/ 01430750.2012.740421 Behera P, Murugan S, Nagarajan G (2014) Dual fuel operation of used transformer oil with acetylene in a DI diesel engine. Energy Convers Manag 87:840–847. https://doi.org/10.1016/j.enconman.2014.07.034 Belagur VK, Chitimini VR (2010) Effect of injector opening pressures on the performance, emission and combustion characteristics of DI diesel engine running on honne oil and diesel fuel blend. Therm Sci 14(4):1051–1061. https://doi.org/10.2298/TSCI1004051B Channapattana SV, Pawar AA, Kamble PG (2015) Effect of injection pressure on the performance and emission characteristics of VCR engine using honne biodiesel as a fuel. Mater Today Proc 2(4-5): 1316–1325. https://doi.org/10.1016/j.matpr.2015.07.049 Gumus M, Sayin C, Canakci M (2012) The impact of fuel injection pressure on the exhaust emissions of a direct injection diesel engine fueled with biodiesel-diesel fuel blends. Fuel 95:486–494. https:// doi.org/10.1016/j.fuel.2011.11.020. Hilden DL, Stebar RF (1979) Evaluation of acetylene as a spark ignition engine fuel. Energy Res Soc Sci 3(1):59–71. https://doi.org/10. 1002/er.4440030107 Imdadul HK, Rashed MM, Shahin MM, Masjuki HH, Kalam MA, Kamruzzaman M, Rashedul HK (2017) Quality improvement of biodiesel blends using different promising fuel additives to reduce fuel consumption and NO emission from CI engine. Energy Convers Manag 138:327–337. https://doi.org/10.1016/j.enconman. 2017.01.077 Jaichandar S, Annamalai K (2013) Combined impact of injection pressure and combustion chamber geometry on the performance of a biodiesel fueled diesel engine. Energy 55:330–339. https://doi.org/ 10.1016/j.energy.2013.04.019 Jindal S, Nandwana BP, Rathore NS, Vashistha V (2010) Experimental investigation of the effect of compression ratio and injection pressure in a direct injection diesel engine running on Jatropha methyl ester. Appl Therm Eng 30(5):442–448. https://doi.org/10.1016/j. applthermaleng.2009.10.004 Lakshmanan T, Nagarajan G (2009) Performance and emission of acetylene-aspirated diesel engine. Jordan J Mech Indust Eng 3(2): 125–130 Lakshmanan T, Nagarajan G (2010a) Experimental investigation of timed manifold injection of acetylene in direct injection diesel engine in dual fuel mode. Energy 35(8):3172–3178. https://doi.org/10.1016/j. energy.2010.03.055 Lakshmanan T, Nagarajan G (2010b) Experimental investigation on dual fuel operation of acetylene in a DI diesel engine. Fuel Process Technol 91(5):496–503. https://doi.org/10.1016/j.fuproc.2009.12. 010 Lakshmanan T, Nagarajan G (2011) Experimental investigation of port injection of acetylene in di diesel engine in dual fuel mode. Fuel 90(8):2571–2577. https://doi.org/10.1016/j.fuel.2011.03.039 Liu J, Yao A, Yao C (2015) Effects of diesel injection pressure on the performance and emissions of a HD common-rail diesel engine

fueled with diesel/methanol dual fuel. Fuel 140:192–200. https:// doi.org/10.1016/j.fuel.2014.09.109 Nanthagopal K, Ashok B, Raj RTK (2016) Influence of fuel injection pressures on Calophyllum inophyllum methyl ester fuelled direct injection diesel engine. Energy Convers Manag 116:165–173. https://doi.org/10.1016/j.enconman.2016.03.002 Price JWH (2006) An acetylene cylinder explosion: a most probable cause analysis. Eng Fail Anal 13(4):705–715. https://doi.org/10. 1016/j.engfailanal.2005.04.014 Purushothaman K, Nagarajan G (2009) Effect of injection pressure on heat release rate and emissions in CI engine using orange skin powder diesel solution. Energy Convers Manag 50(4):962–969. https:// doi.org/10.1016/j.enconman.2008.12.030 Quadri SAP, Masood M, Ravi Kumar P (2015) Effect of pilot fuel injection operating pressure in hydrogen blended compression ignition engine: an experimental analysis. Fuel 157:279–284. https://doi.org/ 10.1016/j.fuel.2015.04.068 Ryu K (2013) Effects of pilot injection pressure on the combustion and emissions characteristics in a diesel engine using biodiesel-CNG dual fuel. Energy Convers Manag 76:506–516. https://doi.org/10. 1016/j.enconman.2013.07.085 Sastry GRK, Deb M, Panda JK (2015) Effect of fuel injection pressure, isobutanol and ethanol addition on performance of diesel-biodiesel fuelled D.I. diesel engine. Energy Procedia 66:81–84. https://doi. org/10.1016/j.egypro.2015.02.043 Sayin C (2011) An experimental investigation on the effect of injection pressure on the exhaust emissions of a diesel engine fueled with methanol-diesel blends. Energy Sources Part A Recover Util Environ Eff 33(23):2206–2217. https://doi.org/10.1080/ 15567030903419471 Sayin C, Gumus M, Canakci M (2012) Effect of fuel injection pressure on the injection, combustion and performance characteristics of a DI diesel engine fueled with canola oil methyl esters-diesel fuel blends. Biomass Bioenergy 46:435–446. https://doi.org/10.1016/j. biombioe.2012.07.016 Shehata MS, Attia AMA, Razek SMA (2015) Corn and soybean biodiesel blends as alternative fuels for diesel engine at different injection pressures. Fuel 161:49–58. https://doi.org/10.1016/j.fuel.2015.08.037 Srivastava AK, Soni SL, Sharma D, Sonar D, Jain NL (2017) Effect of compression ratio on performance, emission and combustion characteristics of diesel–acetylene-fuelled single-cylinder stationary CI engine. Clean Techn Environ Policy 19(5):1361–1372. https://doi. org/10.1007/s10098-017-1334-0 Sudheesh K, Mallikarjuna JM (2013) Diethyl ether as an ignition improver for acetylene-fuelled homogeneous charge compression ignition operation: an experimental investigation. Int J Sustain Energy 34(9): 561–577. https://doi.org/10.1080/14786451.2013.834338 Syed A, Quadri SAP, Rao GAP, Mohd W (2017) Experimental investigations on DI (direct injection) diesel engine operated on dual fuel mode with hydrogen and mahua oil methyl ester (MOME) as injected fuels and effects of injection opening pressure. Appl Therm Eng 114:118–129. https://doi.org/10.1016/j.applthermaleng. 2016.11.152 Wei L, Geng P (2016) A review on natural gas/diesel dual fuel combustion, emissions and performance. Fuel Process Technol 142:264– 278. https://doi.org/10.1016/j.fuproc.2015.09.018 Wulff J et al. (2001) Dual fuel composition including acetylene for use with diesel and other internal combustion engines. Patent No: US 6, 287,351 B1, patent date: Sept 11