Improving Performance of Compressed Natural Gas Fueled Passenger Car Engine by Addition of Hydrogen

Transcription

1 Journal of Scientific & Industrial Research Vol. 77, January 2018, pp Improving Performance of Compressed Natural Gas Fueled Passenger Car Engine by Addition of Hydrogen A K Sehgal 1 *, M Saxena 2, S Pandey 3 and R K Malhotra 4 * 1 Indian Oil Corporation Ltd, Faridabad, India 2 Univeristy of Technology and Management, Shillong, India 3 University of Petroleum and Energy Studies, Dehradun, India 4 Petroleum Federation of India, New Delhi, India Received 06 October 2016; revised 05 June 2017; accepted 07 October 2017 Hydrogen is a clean fuel that can be used as sole fuel or blends with compressed natural gas (CNG) in the spark ignition engines. Blending of hydrogen in CNG improves the burning velocity and calorific value of CNG. Engine tests were carried out using CNG and optimized fuel blend of 18%HCNG for comparing the engine performance and emissions behavior. Marginal improvement in engine performance (up to 2%) and significant reduction in emissions with18%hcng compared to neat CNG. The brake specific fuel consumption was 5% lesser compared to CNG. Replacement of methane by hydrogen in the 18%HCNG blend reduced the HC emissions by ~20% and NOx emissions was increased by ~ 10-20% compared to CNG. 18% HCNG decreased the methane emissions up to 25% compared to CNG. The investigation showed that 18% HCNG has given better performance and emissions compared to CNG. Keywords: Hydrogen, Compressed Natural Gas, Emissions, Methane Emissions Introduction Natural gas is a naturally occurring form of fossil energy. Utilization of natural gas as fuel for internal combustion engines was almost restricted to stationary applications prior to World War II. Compressed natural gas is successfully utilized in many parts of the world such as Argentina, Russia, Italy and India for transport vehicles such as taxis and buses Natural gas is primarily composed of methane but has other hydrocarbon components in small amount as well such as propane, butane and pentane, and also to some extent inert components such as nitrogen and carbon dioxide. It has high hydrogen to carbon (H/C) ratio and high research octane number (RON). Due to the slow flame speed and the poor lean-burn capability of compressed natural gas, the spark ignited engine running on CNG has disadvantages such as large cycle-by-cycle variations and poor lean-burn capability 1-3. Hydrogen is a promising alternative fuel which has been receiving more and more attention all over the world in recent years. Hydrogen is the least polluting fuel that can be used in engines. Hydrogen combustion does not *Author for Correspondence sehgalak@indianoil.in produce any major pollutants such as CO, HC, SOx, smoke and other toxic metals except NOx. Hydrogen can be produced from renewable sources such as biomass and water as well as from non-renewable sources. Hydrogen is a suitable gaseous fuel for SI and CI engines 4-8. The higher self ignition temperature of hydrogen (858 K) allows the use of higher compression ratios. Hydrogen can be ignited at low ignition energy (0.02mJ) compared to methane (0.28mJ) at stoichiometric conditions. Hydrogen gas can be inducted into the engine through carburetion, port injection and direct injection Addition of small amount of hydrogen to natural gas (5 to 30% by volume) improves the properties of the natural gas such as higher flame speed and wider flammability limit Some studies investigated the effect of various hydrogen ratios in HCNG (hydrogen enriched compressed natural gas) fuels on combustion and emission characteristics of a turbocharged spark ignition natural gas engine at idling conditions. HCNG blends significantly reduced CH4 & CO emissions but increased NOx emissions From the literature review, it is clear that a number of research works have published using HCNG blends as fuel for dedicated natural gas engines. Limited number of research publications is available on the use of HCNG

2 62 J SCI IND RES VOL 77 JANUARY 2018 blends in a passenger car bifuel engine. We have conducted studies using different blends of hydrogen compressed natural gas (up to 25% H2 in CNG) to analyse the fuel composition effects on the engine performance and emissions at our IOC R&D Centre. The objective of the present study is to investigate the performance and exhaust emissions of the engine fueled with CNG and 18%CNG and operating at full throttle conditions for different speed conditions. Experimental setup The engine transient dynamometer test bench is installed in a climate controlled test cell which is capable of maintaining the test cell temperature ranges between -5 to +45 C. The test bench consists of a 4 cylinder, MPFI gasoline engine, 120 kw asynchronous dynamometer and fluid conditioning systems, and gas emission measuring equipment. The test engine specification is given in Table 1 and the Table 1 Engine Specification Engine Type Gasoline / CNG Engine Fuel system Multi point fuel injection Engine size 1196 cc No. of cylinders valves / 4 4 cylinder Compression ratio 9.9 Maximum torque 101 rpm Maximum power rpm schematic of the experimental setup is shown in Figure 1. AVL Puma Open 5.0 test bed automation system controls the dynamometer, fluid controlling systems and emission measuring equipment is interfaced with the engine test bed. The test cycles are programmed in the Puma for the automatic operation of test run. A combustion air system is located in the plant room adjacent to the test cell and consists of an AVL ACS1200 unit and an air dryer to control the humidity of the incoming air. The controlled temperature air enters the engine intake system through the ABB make air mass measuring equipment. The system is equipped with a coolant and oil temperature control systems which are capable of maintaining the coolant temperature of 70 to 120 C and oil temperature of 70 to 140 C. A gas mass flow meter is used to measure the mass of gaseous fuel entering the engine. Horiba 7100 DEGR is an integrated gas analyzer that combines various emission detectors together by using the same sample point and is used for gaseous emission measurement. A thermally insulated sample probe is installed ahead of the after treatment devices to avoid condensation of particulates during measurement. Test fuel Gas chromatography is used to analyse the composition of test fuels. The compositions of test fuels of CNG and 18% HCNG are given in Table 2. Fig. 1 Schematic of the experimental setup

3 MALHOTRA et al.: IMPROVING PERFORMANCE OF CNG FUELED PASSENGER CAR 63 Test methodology Engine tests were carried out at full throttle opening condition using CNG and 18%HCNG HCNG on the gasoline engine at 25 C ambient conditions in the weather controlled test cell. The engine test bed control parameters for the test are given in Table 3. Throttle position is maintained at 100% opening (WOT) and speed increased from 1000 to 6500 rpm at a regular interval of 1000 rpm. The engine performance parameters such as power, torque & fuel consumption, and emission parameters such as CO, THC, NOx & CH 4 were measured. The average of Table 2 Composition of HCNG blends S.No Type of compounds CNG 18% HCNG 1 Hydrogen Methane CO Nitrogen Oxygen Ethane Propane i-butane n-butane Table 3 Test conditions Engine parameters Value Test cell temperature 25±1 C Intake air temperature 25±1 C Coolant temperature 90±1 C Oil temperature 95±1 C Relative Humidity 50±1 % 60 second measurement data is used for the analysis (Table 3). Results and Discussions Engine performance Figure 2 shows the plot of the power, torque and brake specific fuel consumption of the engine at different speeds at full throttle conditions. It is observed that the measured power for 18%HCNG are up to 2.0% higher compared to CNG over the entire speed range. Higher flame speed of hydrogen compared to CNG improved the combustion characteristics of CNG and thereby improved the power. The BSFC of the engine decreased till 3000 rpm and further it increased. The similar trend was observed for the both test fuel. The BSFC of the engine for the 18%HCNG blend is lower than neat CNG for the all speed conditions. The 18% HCNG blend decreased the BSFC 5.0% in comparison with CNG. This is due to higher calorific value of the blends and improved combustion efficiency. The combustion efficiency is directly dependent on the C/H ratio; more hydrogen per carbon lowered the oxidation state of the fuel thus releasing more energy during combustion resulting in comparatively higher temperatures. Engine exhaust emissions Figure 2 depicts engine exhaust emissions of the engine for the various speed conditions at full throttle conditions. Reduction in HC emissions with increase in speed was observed for the all test fuels. The quenching gap of hydrogen is mm whereas 0.25 mm for methane which enables more complete combustion of fuel air mixture adjacent to cylinder Fig. 2 Engine performance

4 64 J SCI IND RES VOL 77 JANUARY 2018 walls and crevice volumes thus further reducing HC emission. Moreover, the addition of hydrogen in CNG increased the laminar flame speed and that decreased the amount of unburned hydrocarbons in the exhaust. All these factors reduced the CO and HC emission with 18% HCNG blends compared to that of CNG. Reduction in methane emissions with increase in speed was observed for both fuels. Higher reduction in methane emissions was observed at low speeds (up to 25%) with 18% HCNG. Blending of hydrogen in CNG replaced the hydrocarbon thereby reduction in methane emissions was observed (Figure 3). NOx formation in IC engines depends on oxygen concentration, peak temperature, and duration of exposure at peak temperatures. Higher burning velocity of hydrogen in 18% HCNG blend accelerated the rate of burning of fuel and thereby increased NOx emissions. It is observed that 18% HCNG increased the NOx emissions by 10-20% respectively over the speed range of rpm. Conclusions Engine dynamometer tests were carried out on a spark ignition passenger car engine to assess the performance and emissions characteristics of engine using CNG and 18% HCNG for the various engine speeds at full throttle conditions. Based on the test results, the following conclusions can be drawn. Engine power was increased up to 2% with 18% HCNG and reduction in brake specific fuel consumption was up to 5% with 18%HCNG compared to CNG Up to 20% reduction in HC with 18%HCNG compared to CNG Fig. 3 Engine exhaust emissions 10-20% increase in NOx emissions with 18% HCNG compared to CNG 18% HCNG decreased the methane emissions up to 25% compared to CNG The 18% HCNG blend has shown better performance and emissions characteristics over the entire operating range at full throttle conditions compared to CNG. Acknowledgement First author express his thanks to the Management of Indian Oil R&D Centre for encouragement, support and permission to publish this paper. Authors also thank Dr Reji Mathai, Dr. Dheer Singh, Dr. A. S. Ramadhas & Mr. P.K. Singh for their contribution in this work. References 1 Aslam M I, Masjuki H H, Kalam M A, Abdesselam H, Mahila T M I & Amalina M A, An experimental investigation of CNG a an alternative fuel for a retrofitted gasoline vehicle, Fuel, 85(2006) Rao G L N & Ramadhas A S, Compressed natural gas, Ed: A S Ramadhas, Alternative fuels for transportation, CRC Press, (2010). 3 Jaihal S A & Reddy T S, CNG: An alternative fuel for public transport, J Sci Ind Res, (2006) Sherif SA, Barbir F, Veziroglu TN. Principles of hydrogen energy production, storage and utilization, J Sci Ind Res, 62 (2003) Das L M, Hydrogen-oxygen reaction mechanism and its implication to hydrogen engine combustion, Int J Hydrogen Ener, 21(8) (1996) Karim G A, Hydrogen as spark ignition engine fuel, Int J Hydrogen Ener, 28 (2003) Lynch F E, Parallel induction: A simple fuel control method for hydrogen engines, Int J Hydrogen Ener, 8 (1983)

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