Effect of Water Injection in Acetylene-Diesel Dual Fuel

Proceedings of the ASME 2012 Internal Combustion Engine Division Fall Technical Conference ICEF2012 September 23-26, 2012, Vancouver, BC, Canada

ICEF2012-92145 Effect of Water Injection in Acetylene-Diesel Dual Fuel DI Diesel Engine T. Lakshmanan, Professor Professor, RMK engineering college, Tamilnadu,India,009100 9840154392, [email protected]

A.Khadeer Ahmed, Assistant Professor, AMS college of engineering, Tamilnadu, India

G. Nagarajan, Professor, College of Engineering, Anna University, Chennai. India – 600025 ABSTRACT Gaseous fuels are good alternative fuels to improve the energy crisis of today’s situation due to its clean burning characteristics. However, the incidence of backfire and knock remains a significant barrier in commercialization. With the invention of latest technology, the above barriers are eliminated. One such technique is timed injection of water into the intake port. In the present investigation, acetylene was aspirated in the intake manifold of a single cylinder diesel engine, with a gas flow rate of 390 g/h, along with water injected in the intake port, to overcome the backfire and knock problems in gaseous dual fuel engine. The brake thermal efficiency and emissions such as NOx, smoke, CO, HC, CO2 and exhaust gas temperature were studied. Dual fuel operation of acetylene induction with injection of water results in lowered NOx emissions with complete elimination of backfire and knock at the expense of brake thermal efficiency.

at low power outputs gaseous fuel remains unburned leading to poor performance. The gaseous fuel used, pilot fuel quantity, airfuel ratio and intake temperature are the important variables controlling the combustion and performance of the dual fuel engines at light loads. At higher loads admission of the gaseous fuel results in very high combustion rate leading to backfire and knock. Haragopala et al [2] conducted experiments on a single cylinder, CI engine using hydrogen as a fuel in dual-fuel mode. It was reported that at part loads, hydrogen induction lowers the thermal efficiency, whereas at full load the thermal efficiency was higher than diesel operation. This can be attributed to high diffusion rates of hydrogen and faster energy release due to increased flame propagation velocities. The authors have also stated that it was possible to supply 30 % of energy input through hydrogen at full load. Further increase in hydrogen proportion caused violent knocking. Charge dilution methods, such as manifold water introduction and exhaust gas recirculation (EGR) are likely to increase the hydrogen substitution. Nagarajan et al [3] used hydrogen as an air-enrichment medium with diesel as an ignition source in diesel engine to improve the engine performance and reduce emissions. Hydrogen-air enriched system in diesel engine enabled the realization of higher brake thermal efficiency, but results in knock. NOx and smoke concentration decreases with lean mixtures of hydrogen. Saravanan et al [4] investigated the effect of cooled EGR in hydrogen-enriched single cylinder diesel engine. They concluded that brake thermal efficiency increases by 6 % without EGR; with cooled EGR, it was lower than dual-fuel engine and higher than neat diesel at full load operation. Ashok Kumar et al. [5] studied the suitability of acetylene in a SI engine along with EGR and reported that emissions drastically reduced on par with hydrogen engine with marginal increase in thermal efficiency. Lakshmanan et al [6] used acetylene in a single cylinder diesel engine in carburetion technique at various gas flow rates. Knock limited the maximum substitution at 390 g/h of gas flow

INTRODUCTION Diesel engines are considered one of the environmental friendly engines due to higher thermal efficiency, durability and lower operational cost. Nevertheless, the major problems associated with diesel engine are emissions of smoke, NOx and particulate matter. Hence, stringent emission norms and decreasing in availability of fossil fuels necessitated the research for alternative fuels. The promising alternative fuels are CNG, LPG, acetylene, hydrogen, biodiesel and ethanol. Among the alternative fuels, gaseous fuels possess excellent combustion properties. Gaseous fuel in a diesel engine is substituted by dual fuel principle or by providing a glow plug. In dual fuel engines, primary fuel is the gaseous fuel, which is usually inducted along with air, and a small amount of pilot diesel fuel is injected. The pilot fuel auto ignites and acts as an intense ignition source for primary gaseous fuel. Karim[1] has reported that in dual fuel engines, 1

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rate. There was higher NOx emission with reduction in smoke, HC, CO and CO2 emissions with marginal decrease in efficiency. It is observed from literature that the major problems with gaseous dual fuel engines are higher NOx emissions, high rate of pressure rise, poor part load performance, backfire and knocking at full load. The reduction in NOx emission, preignition and knock suppression can be achieved by inducting charge diluent such as helium, nitrogen, EGR, water injection, retarding injection timing, etc., Mathur [7] and Prabhukumar [8]. The objective of the present experimental work is to examine the effect of water injection into the intake port of single cylinder acetylene-diesel dual fuel engine on the exhaust emissions and performance characteristics. EXPERIMENTAL SETUP A single cylinder 4-stroke air cooled diesel engine with compression ratio of 17.5, producing 4.4 kW power at 1500 rpm is used for acetylene-diesel dual fuel operation. Nozzle opening pressure of diesel is 200 bar with injection timing 23 oCA bTDC. The engine was modified to work in acetylene-diesel dual fuel mode with diesel as the injected primary fuel and acetylene as the inducted secondary fuel by carbureting it into the inlet manifold through a flame trap and a non-return valve.

1. Diesel Engine 2. Dynamomete 3.Inlet manifold 4. Non return valve 5. Gas flow meter 6. Flow control valve 7. Flame trap 8. Acetylene cylinder 9. Pressure regulator 10. Inlet port water injector 11. Water pump 12. ECU for water injector 13. Surge tank 14. Diesel fuel tank 15. U-tube manometer 16. Burette for diesel Fig. 1 Schematic of the experimental setup EXPERIMENTAL PROCEDURE Initially, tests were conducted with diesel at the rated speed and variable load conditions. Tests were conducted on acetylene diesel dual fuel engine with water injection at all loads. Water was injected during the intake stroke and injection flow rate was varied from 200 g/h to 400 g/h. Acetylene quantity was fixed at 390 g/h, which was found in the previous work of the authors [6]. All the tests were conducted at the rated speed of 1500 rpm for various loads.

Table.1 Physical and combustion properties of fuels Properties

Acetylene

Hydrogen

Formula

C2H2

H2

Density kg/m3 (At 1.01325 bar & 293o K)

1.092

0.08

Auto ignition temperature (o K ) Stoichiometeric air fuel ratio, (kg/kg) Flammability Limits (Volume %) Adiabatic flame temperature (o K) Lower Calorific Value (kJ/kg) Max deflagration speed (m/sec)

Diesel C8 – C20 840

578

845

527

13.2

34.3

14.5

2.5 – 81

4 – 74.5

0.6 – 5.5

2500

2400

2200

48,225

1,20,000

42,500

1.5

3.5

0.3

RESULTS AND DISCUSSION Experiments were conducted in acetylene-diesel dual fuel mode with the maximum flow rate of acetylene maintained at 390 g/h, with water injection into the intake port for various water flow rate at 200 g/h, 300 g/h and 400g/h and the results are presented. Performance parameters The variation of brake thermal efficiency with load for various flow rates of water in acetylene diesel dual fuel operation is shown in Fig. 2. The brake thermal efficiency in water injection technique at full load is found to be 25 % at 400 g/h of water flow rate, 28 % at 390 g/h of acetylene flow rate and for diesel it is 29 %. Injection of water in acetylene-diesel dual fuel operation results in decrease in brake thermal efficiency for the same acetylene flow rate. Vaporization of water decreases the temperature of the mixture at the end of compression stroke and hence allows more gaseous fuel to escape the combustion process as a result of quenching.

A provision was made in the intake port to fix the solenoid operated electronic water injector to inject water. The exhaust gas constituents (CO, CO2, HC and NOx) were measured by Qrotech, QRO-401 gas analyzer, and Bosch smoke meter for the measurement of smoke. The schematic of the experimental setup is shown in Fig.1. The properties of fuel are given in Table 1.

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The water injection technique reduces NOx emission due to vapourisation of water, which decreases the maximum cycle temperature and therefore reduces the chemical reaction in gas phase to produce thermal NOx.

Fig. 2 Variation of Brake thermal efficiency with load

Fig. 4 Variation of NOx with load

The exhaust gas temperature at full load is depicted in Fig. 3. It is 301° C at 390 g/h, of acetylene-diesel dual fuel operation and 444° C in the case of diesel operation and with water injection it is 259º C at 400 g/h of water flow rate at full load. The heat absorbed by the injected water results in decreasing the exhaust gas temperature.

The variation of smoke level with load is shown in Fig. 5. The smoke level increases with increase in diesel flow rate and at full load; it is 4 BSN (Bosch smoke number) in the case of diesel fuel operation. Smoke increases slightly with water injection into the port when compared to acetylene-diesel operation. The smoke is affected by the change of temperature and rate of fuel-air mixture [9]; while the temperature effect is readily appreciated due to vaporization of water.

Fig. 5 Variation of Smoke with load

Fig.3 Variation of Exhaust gas temperature with load

The variation of unburned hydrocarbon emissions with load is shown in Fig. 6. unburned hydrocarbon emissions vary from 0.22 g/kWh at low load to 0.07 g/kWh at full load in diesel operation. For dual fuel operation of acetylene, unburned hydrocarbon varies from 0.13 g/kWh at low load to 0.04 g/kWh at full load for the gas flow rate of 390 g/h. With water injection in dual fuel operation, the unburned hydrocarbon emissions increase

Emission Parameters It can be observed from Fig.4 that NOx emission is 11.62 g/kWh at maximum output with neat diesel fuel operation. In dual fuel operation with acetylene induction at full load, NOx emission is 16.93 g/kWh at 390 g/h of acetylene and 12.09 g/kWh at 400 g/h of water flow rate in dual fuel mode.

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marginally compared to dual fuel operation. It varies from 0.21 g/kWh at low load to 0.06 g/kWh at full load at 400 g/h of water injection. The reduction in unburnt hydrocarbon in water injection in dual fuel mode at low loads, is due to quenching effect leading to incomplete combustion. At high loads the increase in unburned hydrocarbon emissions level is negligible.

g/h of acetylene flow rate and 826 g/kWh in diesel operation at full load. The CO2 emission is lowered in dual fuel operation, due to the reduction in overall C/H ratio of the total fuel injected into the engine. In the case of dual fuel operation with water injection it is lowered due to incomplete combustion of the charge and lower C/H ratio of acetylene.

Fig. 6 Variation of Unburned HC with load A provision was made in the intake port to fix the solenoid operated electronic water injector to inject water. The exhaust gas constituents (CO, CO2, HC and NOx) were measured by Qrotech, QRO-401 gas analyzer, and Bosch smoke meter for the measurement of smoke. The schematic of the experimental setup is shown in Fig.1. The properties of fuel are given in Table 1.

Fig. 8 Variation of Carbondioxide with load Combustion Parameter The variation of cylinder pressure with crank angle is shown in Fig. 9. At full load the peak pressure is about 72 bar in diesel operation and with dual fuel operation the peak pressure is

Fig. 7 Variation of Carbonmonoxide with load Fig. 9 Variation of Cylinder pressure with crank angle at full load 91 bar at 390 g/h of acetylene, with water injection in dual fuel operation the peak pressure is 71 bar at 400 g/h of water injection at maximum load. The peak pressure for acetylene-diesel dual

The variation of CO2 emissions with load is shown in Fig. 8. CO2 emissions are lower compared to diesel, the minimum being 600.53 g/kWh at 400 g/h, 626.66 g/kWh at 300 g/h, whereas for dual fuel operation without water injection CO2 emission is 679.75 g/kWh at maximum flow rate of 390

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fuel engine is advanced by 6° CA at 390 g/h of acetylene, with water injection the peak pressure is advanced by 1° CA at 400 g/h of water injection, when compared to the peak pressure occurrence of diesel at full load. The advancement in peak pressure for acetylene combustion is due to the instantaneous combustion of acetylene compared to diesel fuel. The delay in the occurrence of peak pressure in case of water injection in acetylene-diesel operation is due to reduction in the intake charge temperature.

bTDC: Before Top Dead Centre

REFERENCES [1] G.A. Karim, The dual-fuel engine of the compression ignition type-prospects, problems and solutions: A review, SAE Paper No 831073. [2] B. Haragopala Rao, K.N. Srivatsava, H.N. Bhaktan , Hydrogen for dual fuel Engine operation, International Journal of Hydrogen Energy, 8 (1983) 381-384. [3] G. Nagarajan, N. Saravanan, An experimental investigation of hydrogen-enriched air induction in a diesel engine system, International Journal of Hydrogen Energy, 33 (2008) 1769-1775. [4] S. Saravanan, G. Nagarajan, C. Dhanasekaran, K.M. Kalaiselvan, An experimental investigation on hydrogen as a dual fuel for diesel engine system with exhaust gas recirculation technique, Renewable Energy, 32 (2007) 1581–1593. [5] V. Ashok Kumar, Mohammed Sikander, Najmul Islam Khan, Experimental investigation on use of welding gas (acetylene) on SI engine, Proceedings of AER Conference, IIT Mumbai, India, (2006) 422-427. [6] T. Lakshmanan, G. Nagarajan, Experimental investigation of acetylene in DI diesel engine in dual fuel mode, Fuel Processing Technology, 91 (2010) 496–503. [7] H.B. Mathur, L.M. Das, T.N. Patro, Hydrogen fuelled diesel engine: Performance improvement through charge dilution techniques, International Journal of Hydrogen Energy, 18 (1993) 421–431. [8] C.P. Prabhu Kumar, S. Swaminathan, B. Nagalingam, K.V. Gopala Krishnan, Water induction Studies in a Hydrogen Diesel dual fuel engine, International Journal of Hydrogen Energy, 12 (1987) 177–186. [9] G. Greeves, A. Khan, G. Onion, Effects of water introduction on diesel engine combustion and emissions, Proceedings of 16th International Symposium on Combustion, (1976) 321–336.

CONCLUSION Based on the experimental study the following conclusions are drawn: Brake thermal efficiency decreases with injection of water due to the escape of gaseous fuel during the combustion process as a result of quenching. Water injection into the inlet port leads to a significant reduction in NOx levels. At full load, NOx reduced from 16.93 g/kWh for acetylene without water injection to 12.00 g/kWh acetylene with a water flow rate of 400 g/h. Smoke increases marginally, which is 3.0 BSN for acetylene without water injection and 3.5 BSN for acetylene with water injection at full load. HC emissions increase marginally when compared with acetylene diesel dual fuel operation. CO emissions follow a similar trend like HC emissions. Peak pressure is decreased and occurrence of peak pressure is delayed in acetylene with water injection than acetylene without water injection. Timed port injection of water has a significant potential to reduce the formation of thermal NOx and possibility of backfire at the expense of brake thermal efficiency in carburetion mode. However, the values are lower than diesel operation.

NOMENCLATURE CNG: Compressed Natural Gas LPG: Liquefied Petroleum Gas EGR: Exhaust Gas Recirculation

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