Performance Analysis of a Natural Gas Engine System Fueled with Ammonia/Hydrogen

Performance Analysis of a Natural Gas Engine System Fueled with Ammonia/Hydrogen

Jun Li 1

Department of Chemical Engineering, Nagoya University,

Nagoya, Japan

Tao Zeng 2

Department of Chemical Engineering, Nagoya University,

Nagoya, Japan

Hongyu Huang 3

Guangzhou Institute of Energy Conversion Chinese Academy of Sciences Guangzhou, China

Masayoshi Yagami 4

Department of Chemical Engineering, Nagoya University,

Nagoya, Japan

Takehiro Esaki 5

Department of Chemical Engineering, Nagoya University,

Nagoya, Japan

Noriyuki Kobayashi 6

Department of Chemical Engineering, Nagoya University,

Nagoya, Japan

Abstract This study evaluates a natural gas spark-ignition engine performance and efficiency fueled with ammonia/ hydrogen (NH3/H2). NH3 and H2 from NH3 decomposition as fuels of a gas engine system has been proposed in this research. The effects of the direct injection of gaseous NH3 together with H2 from NH3 decomposition on the engine performance and efficiency have been experimentally investigated. The results show that a maximum of 60 % NH3 addition (LHV basis) can be reached when the gas engine fueled by NH3 and CH4 with a fixed rotation speed of 1950 rpm. The gas engine operates stably at a maximum high addition ratio of 92.5% NH3+H2 (LHV basis) addition to total fuel under fixed rotation speed with tiny vibration of 1.0%, showing a feasible replacement of NH3+H2 as major fuel of the gas engine fueled by CH4. The cylinder pressure of gas engine decreases with the addition of NH3, while increases with the addition of H2. A lower energy density of NH3 and H2 leads a lower power generation efficiency of the gas engine when fueled by NH3/H2/CH4 compared with CH4.

Keywords ammonia; hydrogen; gas engine; cylinder pressure; engine efficiency

1. INTRODUCTION

   With the increasing strictness of governmental regulation of greenhouse gas emissions, together with other pollutant emissions such as carbon monoxide (CO), unburned hydrocarbons (HCs), nitrogen oxides (NOx), and particulate matter (PM). The search for carbon-free alternatives fuels is one important concern of our society. Many studies have evaluated H2 as one of the most favorable candidates because no CO, CO2 or soot is formed and only water is formed in the utilization of H2 in internal combustion engines and fuel cells [1,2]. However, many challenges still exist in using H2 as a fuel, such as production, storage, and handling issues of H2. On the other hand, ammonia (NH3) is another carbon-free

   alternative fuel, which has received much less attention. NH3 is also a typical H2 storage material with a highest energy density of 17.8 among other H2 storage materials. Furthermore, NH3 is widely used as heat medium of refrigerator, fertilizer, and de-NOx material, the production, storage, handling, and distribution facilities of NH3 are commercially available worldwide. NH3 can be potentially synthesized by renewable energy sources such as wind, solar, and biomass. NH3 can be stored in the liquid state at 20 °C and 8.0 atm, which is much easier than the storage of H2 [3]. But NH3 exhibits a low heating value (LHV, 18.8 MJ/kg), a high latent heat of vaporization (1370 kJ/kg), and a high ignition temperature (651°C). Because of these three factors with a slow burning velocity (5-13 cm/s), both compression- ignition and spark-ignition engines fueled by NH3 are still challenging [4-7].

   In order to eliminate the unfavorable combustion properties of NH3, many studies on spark-ignition and compression-ignition engines fueled NH3 together with gasoline or H2 have been performed [5,8-15]. The addition of gasoline or H2 can help NH3 ignition in the combustion chamber because of high ignition energy of NH3. No sufficient ignition energy will lead misfire and cause air pollution and hazard to health because of unburned NH3. Furthermore, the addition of gasoline or H2 can improve the flame propagation and burning velocity of NH3 combustion in the chamber. Since H2 is more reactive and has a higher burning velocity (280-300 cm/s) [3], the addition of H2 is more reactive than gasoline for improving NH3 combustion [16-20].

   In this study, the analysis of a gas engine system fueled by NH3/H2/CH4 was investigated. Methane and H2 was used as the second fuel to improve NH3 combustion. The ration

   numbers of the gas engine and cylinder pressure at different fuel composition of NH3/H2/CH4 are presented. The power generation efficiency at different fuel composition of NH3/H2/CH4 is also measured.

2. EXPERIMENTAL APPARATUS AND PROCEDURE

   The full schematic diagram of the gas engine system fueled by NH3/H2/CH4 is shown in Fig. 1. The system consists of a fuel supply system, a fuel mix chamber, a gas engine, a heat recovery system to provide hot water. Engine ration number, cylinder pressure, and engine power are measured. The mass flow of NH3, H2, and CH4 were controlled by commercial mass flow controllers (Azbil, CMS0050) with an accuracy ±1.0% of the full scale delivered. The supply pressure of NH3, H2, and CH4 are 0.1 Mpa, 0.1 Mpa, and 0.2 Mpa, respectively. The cylinder pressure was measured using a Kistler 6118BFD16 piezo- electric pressure transducer together with a Kistler 5010 charge amplifier. The engine power was measured by a digital multi-meter (Graphtec, CM-211).

   NH /H /CH

   Fig. 1. Full schematic diagram of the gas engine system fueled by

   3 2 4

   The experiment utilized an extended expansion linkage engine commercially produced by Honda cooperation for family power generation. Detailed specifications for the engine are shown in Table 1. The engine is a four stroke, one cylinder, spark-ignition engine with an intake stroke volume of 110 cm3 and an exhaust stroke volume of 163 cm3. The fixed rate speed of the engine is 1950 rpm with a fixed power generation efficiency of 26.3 % when fueled by CH4. A heat recovery system for providing hot water is used as a set for exhaust recovery, and the exhaust heat recovery efficiency is higher as 65.7 % when fueled by CH4, leading a high total efficiency of 92 %. Furthermore, in order to achieve the emission standard, a set of selective catalytic reduction of NOx is included at the exit of exhaust gas. Those are beneficial when fueled by NH3 and H2.

   Table 1: Extended expansion linkage engine specifications

   Item	Specifications
   Engine model	Honda EXlink
   Engine type	Four stroke, one cylinder, spark- ignition
   Intake stroke volume (cm3)	110
   Exhaust stroke volume (cm3)	163
   Rate speed (rpm)	1950
   Output of electricity (Methane as fuel, kW)	1.0
   Recovery of exhaust heat (Methane as fuel, kW)	2.5
   Efficiency of electricity (Methane as fuel, %)	26.3
   Efficiency of recovery heat (Methane as fuel, %)	65.7

3. RESULTS AND DISCUSSION

   1. Ammonia addition limitation

      In order investigate the possibility of NH3 as fuel of the gas engine; we firstly use NH3 and CH4 as fuel of the gas engine. The limitation of NH3 added as fuel of gas engine has been investigated as shown in Table 2. As shown in Table 2, the air to fuel ratio (A/F) of the engine decreases with the addition of NH3 to the fuel. Furthermore, the gas engine can be perated by NH3/CH4 as fuel when NH3 ration to total fuel below 60%, which shows a possibility of NH3 replacement with CH4 as a fuel of gas engine.

      Run No.	CH4 (LHV)	NH3 (LHV)	Total (LHV)	NH3% (LHV)	A/F
      1	2.35	0.00	2.35	0.0	27.22
      2	1.98	0.30	2.28	13.0	24.54
      3	1.74	0.59	2.33	25.4	21.34
      4	1.61	0.74	2.35	31.4	20.03
      5	1.55	0.89	2.44	36.4	18.50
      6	1.49	1.03	2.52	41.0	17.18
      7	1.36	1.18	2.55	46.4	16.30
      8	1.30	1.33	2.63	50.5	15.25
      9	0.99	1.48	2.47	59.8	15.25

      Table 2 Gas composition of gas engine fueled by NH3/ CH4

      The effects of NH3 ratio to total fuel (LHV basis) on rotation number of gas engine are shown in Fig. 2. It can be seen from Fig. 2, gas engine can be operated stably when NH3 ratio to total fuel (LHV basis) below 20% without vibration of rotation number, as fixed rotation speed of 1950 rpm. While with further increase of NH3 ratio to total fuel, the gas engine becomes unstable with a maximum rotation number change of 100 when NH3 ratio to total fuel is increased to 60%. The unstable operation of gas engine is mainly because of the low burning velocity of NH3 (5 to 13 cm/s), leading a low combustion rate and limits its

      application in the gas engine.

      Fig. 2 Effect of NH3 energy ratio (LHV basis) on rotation number of gas engine fueled by NH3/CH4

      In order to improve the replacement of NH3 to gas engine as a practical fuel, NH3+H2 is added as fuel of gas engine. The ratio of NH3/H2 (volume ratio) has decided to be 1.25:1.00 according to the burning velocity of NH3/H2 mixture, the burning velocity of NH3/H2 mixture at this condition approximately equals that of methane, which can be seen from our past research [3]. The limitation of NH3/H2 mixture added as fuel of gas engine has been investigated as shown in Table 3. As shown in Table 3, the gas engine can be operated only by NH3/H2 as fuel. Whereas, the gas engine can be stably operated about 20s, results from a misfire when fueled by NH3/H2 mixture only. The reason is mainly because of the higher ignition temperature of NH3/H2 mixture, leading a misfire when operated only by NH3/H2 as fuel.

      Table 3 Gas composition of gas engine fueled by NH3/H2/CH4

      Run No.	CH4 (LHV)	NH3 (LHV)	H2 (LHV)	Total (LHV)	NH3+H2% (LHV)	A/F
      1	2.35	0.00	0.00	2.35	0.0	27.22
      2	1.86	0.30	0.14	2.30	19.1	21.34
      3	1.55	0.59	0.29	2.43	36.2	16.58
      4	1.30	0.74	0.36	2.40	45.8	15.25
      5	1.11	0.89	0.43	2.43	54.2	13.90
      6	0.99	1.03	0.50	2.53	60.8	12.58
      7	0.87	1.18	0.57	2.62	66.9	11.47
      8	0.74	1.33	0.65	2.72	72.7	10.53
      9	0.62	1.48	0.72	2.82	78.0	9.73
      10	0.49	1.63	0.79	2.91	83.0	9.02
      11	0.37	1.77	0.86	3.01	87.6	8.41
      12	0.25	1.92	0.93	3.10	92.0	7.86
      13	0.19	2.07	1.01	3.26	92.5	7.31
      14	0.00	2.07	1.01	3.08	100.0	7.51

      The effects of NH3+H2 ratio to total fuel (LHV basis) on rotation number of gas engine are shown in Fig. 3. It can be seen from Fig. 3, gas engine can be operated stably without vibration of rotation number, as fixed rotation speed of 1950 rpm. Even at high addition ratio of NH3+H2 to total fuel of 92.5%, the gas engine can be operated at fixed rotation speed with tiny vibration of 1.0%, which shows that the addition of H2 to NH3 fueled engine can increase the stability of the engine. Furthermore, it is necessary to point out that the gas engine has been operated 20s when use 100% of NH3+H2 as fuel, which shows that it is feasible to replace NH3+H2 as major fuel of the gas engine fueled by CH4.

      Fig.3 Effect of NH3+H2 energy ratio (LHV basis) on rotation number of gas engine fueled by NH3/H2/CH4

   2. Combustion performance

   The in-cylinder combustion using NH3/H2/CH4 exhibits characteristics of a conventional spark-ignition engine. Fig. 4 shows the cylinder pressure of gas engine at different fuel composition of NH3/H2/CH4 at 1950 rpm. As shown in Fig. 4, the cylinder pressure of gas engine decrease with the addition of NH3, while increase with the addition of H2. The cylinder pressure of gas engine at NH3/H2/CH4 of 5:4:1.2 (L/min, volume velocity basis) equals to that when fueled by CH4, the energy input at this condition is approximately 1.4 times of that at CH4 (3.2 L/min), which confirms the lesser efficacy of NH3/H2 with respect of CH4.

   Fig. 4 Cylinder pressure of gas engine fueled by NH3/H2/CH4 The power generation efficiency of gas engine is shown

   in Table 4. As shown in Table 4, the efficiency of gas engine reaches the standard efficiency of power generation as shown in Table 1, whereas, the efficiency of gas engine when fueled by NH3/H2/CH4 at 5:4:1.2 (L/min, volume velocity basis) is only 40 % of that of when fueled by CH4 only at 3.2 L/min. This also confirms that the addition of NH3/H2 has a less efficacy than that of CH4 when use NH3/H2 as the alternative fuel of gas engine.

   Table 4 Power generation efficiency of gas engine fueled by NH3/H2/CH4

   Run No.	CH4 (L/min)	NH3 (L/min)	H2 (L/min)	Current (A)	Total (kW, LHV)	Efficiency (%)
   				Ranges (A)
   1	3.2	0	0	4.5	1.90	26.1
   				4.44.6
   2	2.3	5.0	0	2.5	2.55	10.8
   				2.42.5
   3	1.3	5.0	4.0	2.5	2.62	10.5
   				2.42.5

4. CONCLUSIONS

The performance of a spark-ignition gas engine system fueled with ammonia and hydrogen was evaluated in this study. The effects of ammonia and hydrogen as fuel on gas engine performance and efficiency were experimentally investigated. The major conclusions in this study are as follows. A maximum of 60 % NH3 addition (LHV basis) can be reached when the gas engine fueled by NH3 and CH4 with a fixed rotation speed of 19500 rpm .The gas engine operates stably at a maximum high addition ratio of 92.5% NH3+H2 (LHV basis) addition to total fuel under fixed rotation speed with tiny vibration of 1.0%, showing a feasible replacement of NH3+H2 as major fuel of the gas engine fueled by CH4.A lower energy density of NH3 and H2 leads a lower power generation efficiency of the gas engine when fueled by NH3/H2/CH4 compared with CH4.

ACKNOWLEDGMENT

Jun Li is grateful to the C.S.C (China Scholarship Council) for the financial support of his Ph.D thesis.

REFERENCES

1. Zamfirescu C and Dincer I, Using ammonia as a sustainable fuel. J Power Sources; vol. 185, no. 1, pp. 459-465, 2008.

2. Boretti AA, Novel heavy duty engine concept for operation dual fuel H2-NH3, Int. J Hydrogen Energ, vol. 37, no. 9, pp. 7869-7876, 2012.

3. Li J, Huang HY, Kobayashi NY, He ZH, Nagai YH, Study on using hydrogen and ammonia as fuels: combustion characteristics and NOx formation, Int J Energ Res, vol. 38, no. 9, pp. 1214-1223, 2014.

4. Ryu K, Zacharakis-Jutz G, Kong SC, Effects of gaseous ammonia direct injection on performance characteristics of a spark-ignition engine, Appl Energy, vol. 116, pp. 206-215. 2014.

5. Westlye FR, Ivarsson A, Schramn J, Experimental investigation of nitrogen based emissions from an ammonia fueled SI-engine, Fuel, vol. 111, pp. 239-247, 2013.

6. Gross CW, Kong SC, Performance characteristics of a compression- ignition engine using direct-injection ammonia-DME mixtures, Fuel, vol. 103, pp. 1069-1079, 2013.

7. Reiter AJ and Kong SC, Combustion and emissions characteristics of compression-ignition engine using dual ammonia-diesel fuel, Fuel, vol. 90, pp. 87-97, 2011.

8. Mørch CS, Bjerre A, Gøttrup MP, Sorenson SC, Schramm J, Ammonia/hydrogen mixtures in an SI-engine: Engine performance and analysis of a proposed fuel system, Fuel, vol. 90, no. 2, pp. 854- 864, 2011.

9. Frigo S, Gentili R, Doveri N, Ammonia plus hydrogen as fuel in a S.I. engine: Experimental results, SAE Technical Paper, no. 32-0013, pp. 1-8, 2012.

10. Frigo S and Gentili R, Analysis of the behaviour of a 4-stroke Si engine fuelled with ammonia and hydrogen, Int J Hydrogen Energ, vol. 38, no. 3, pp. 1607-1615, 2013.

11. Gill SS, Chatha GS, Tsolakis A, Golunski SE, York APE, Assessing the effects of partially decarbonising a diesel engine by co-fuelling with dissociated ammonia, Int J Hydrogen Energ, vol. 37, no. 7, pp. 6074- 6083, 2007.

12. McGinnis RL, McCutcheon JR, Elimelech M, A novel ammonia carbon dioxide osmotic heat engine for power generation, J Membrane Sci, vol. 305, no. 1-2, pp. 13-19.

13. Grannell SM, Assanis DN, Bohac SV, Gillespie DE, The fuel mix limits and efficiency of a stoichiometric, ammonia, and gasoline dual fueled spark ignition engine, J Eng Gas Turbines Power, vol. 130, no. 042802, pp. 1-8, 2008.

14. Koike M, Miyagawa H, Suzuoki T, Ogasawara K, Ammonia as a hydrogen energy carrier and its application to internal combustion engines, Sustainable Vehicle Technologies, pp. 61-70, 2012.

15. Mariani A, Prati M V, Unich A, Morrone B, Combustion analysis of a spark ignition i. c. engine fuelled alternatively with natural gas and hydrogen-natural gas blends, Int J Hydrogen Energ, vol. 38, no. 3, pp. 1616-1623, 2013

16. Duynslaegher C, Jeanmart H, Vandooren J, Ammonia combustion at elevated pressure and temperature conditions, Fuel, vol. 89, pp. 3540- 3545, 2010.

17. Ryu K, Zacharakis-Jutz G, Kong SC, Performance enhancement of ammonia-fueled engine by using dissociation catalyst for hydrogen generation, Int J Hydrogen Energ, vol. 39, no. 5, pp. 2390-2398, 2014.

18. Liu R, Ting DSK, Checkel D, Ammonia as a fuel for SI engine, SAE Technical Paper, no. 01-3095, pp. 1-7, 2003.

19. Jeong C, Kim T, Lee K, Song S, Chun KM, Generating efficiency and emissions of a spark-ignition gas engine generator fuelled with biogas- hydrogen blends, Int J Hydrogen Energ, vol. 34, no. 23, pp. 9620- 9627, 2009.

20. Lee K, Kim T, Cha H, Song S, Chun KM, Generating efficiency and NOx emissions of a gas engine generator fueled with a biogas-hydrogen blend and using an exhaust gas recirculation system, Int J Hydrogen Energ, vol. 35, no. 11, pp. 5723-5730, 2010.