Development of Electric Power Generator by Using Hydrogen †

: In this research, we developed a hydrogen (H 2 ) electric generator in an H 2 generation system based on chemical reactions. In the experiment, we tested the performance of the H 2 electric generator and measured the amount of H 2 generated. The maximum output was 700 W and the thermal efﬁciency was 18.2%. The theoretical value and measured value were almost the same, and the maximum error was 4%.


Introduction
Recently, the impact of global warming has become serious due to an increase in greenhouse gases emitted from industrial activities [1].The decarbonization of mobility and power generation systems is considered as a countermeasure.One of the representative technologies is the use of internal combustion engines (ICEs) using H 2 as fuel [2].H 2 is attracting much attention as an alternative fuel for automobiles.However, there are few practical examples of electric generators that use H 2 as fuel.The purpose of this research was to develop a small H 2 electric generator that operates stably with a maximum output of 1 kW by improving the fuel supply part of the conventional gasoline electric generator, and establishing an H 2 generation system using chemical reactions.In the previous research [3], a surge tank was introduced to homogenize the mixture of H 2 and air.As a result of measuring the maximum output of the electric generator, power was supplied stably at 800 W. In this research, the effect of the shape of the intake manifold on electric generator performance was confirmed.In addition, the H 2 generation system using a chemical reaction between an aqueous solution of sodium borohydride (NaBH 4 aq) and aqueous solution of citric acid (C 6 H 8 O 7 aq) was adopted as an on-site H 2 generation method, and theoretical and actual values were compared.

Hydrogen Engine Generator Performance Test 2.1. Combustion Characteristics of Hydrogen
The combustion reaction of H 2 is shown in Equation (1).H 2 combines with oxygen (O 2 ) at a high temperature to produce water and thermal energy.H 2 is environmentally friendly because it does not emit carbon dioxide (CO 2 ).However, it also has the disadvantage of producing harmful nitrogen oxides (NOxs) at high temperatures.The main combustion characteristics of H 2 are early ignition and lean burn.Table 1 shows a comparison of the fuel properties of methane (CH 4 ) and H 2 [4].The minimum ignition energy of H 2 is about 1/10 that of CH 4 , indicating that even a small spark burns it.In addition, the flammability range of H 2 is 4 to 75, which indicates lean burn.In terms of  1.

Experimental Method and Conditions
Figure 1 shows the H 2 electric generator test equipment.The electric generator in the experiment adopted a forced air-cooled 4-cycle gasoline overhead valve inverter with a total displacement of 79 cm 3 , a rated output of 1.9 kW, and a compression ratio of 9.4.In the fuel supply system, a supply port injection was used.The H 2 supply port was attached to the bottom of the intake so that it could be mixed with the inflowing air.The surge tank was a box-type one with a capacity of 1670 cm 3 to temporarily store air and make the flow rate uniform.
2H2 + O2 = 2H2O + 248 kJ/mol (1) The main combustion characteristics of H2 are early ignition and lean burn.Table 1 shows a comparison of the fuel properties of methane (CH4) and H2 [4].The minimum ignition energy of H2 is about 1/10 that of CH4, indicating that even a small spark burns it.In addition, the flammability range of H2 is 4 to 75, which indicates lean burn.In terms of flame propagation, H2 has a six times faster speed than CH4.H2 is a material with excellent ignition and combustion properties.It is also susceptible to abnormal combustion such as backfire requiring a preventative measure.The basic experimental conditions are listed in Tabe 1.

Experimental Method and Conditions
Figure 1 shows the H2 electric generator test equipment.The electric generator in the experiment adopted a forced air-cooled 4-cycle gasoline overhead valve inverter with a total displacement of 79 cm 3 , a rated output of 1.9 kW, and a compression ratio of 9.4.In the fuel supply system, a supply port injection was used.The H2 supply port was attached to the bottom of the intake so that it could be mixed with the inflowing air.The surge tank was a box-type one with a capacity of 1670 cm 3 to temporarily store air and make the flow rate uniform.Table 2 shows the experimental conditions.We designed and manufactured three types of intake manifolds to confirm the effect of intake air volume and air-fuel ratio (AFR).Figure 2 shows its appearance.In the experiment, the output was changed from 100 W to 1 kW using a converter.The engine speed was constant at each output, and xperimental Method and Conditions igure 4 shows the H2 generation system.In this system, NaBH4 and C6H8O7 were ed up and reacted in a reactor to generate H2.This reaction produces boric acid and m citrate in addition to H2.These by-products were diverted in the flow path and o the waste tank.The H2 generated is at a high temperature due to the exothermic on and contains water vapor that must be removed.The H2 flow quantity was measusing a flow meter.Therefore, the temperature of H2 was lowered by cooling water easured after being passed through a desiccant.he concentration of the two aqueous solutions used in the experiment was an imnt factor, and precipitation and sticking occurred if the concentration was not appro-.The results of previous research [7] indicated that the NaBH4aq was 33.3 wt.% and 6H8O7aq was 27.0 wt.%.Also, the input ratio of the aqueous solution was 5:6, and the nt was derived from the following formula.Assuming a molecular weight of 37.83 aBH4 and standard conditions (0 °C, 1 atm, and 22.4 L), we calculated the amount of us solution required to generate H2 (25 °C, 1 atm, and 10 L).Equation (2) shows that of H2 is generated from 1 mol of NaBH4, and the amount of NaBH4 can be obtained Equation (3).
rom the results of Equation ( 3), the amount of NaBH4aq with a concentration of 33.3 is given by Equation ( 4).Table 2 shows the experimental conditions.We designed and manufactured three types of intake manifolds to confirm the effect of intake air volume and air-fuel ratio (AFR).Figure 2 shows its appearance.In the experiment, the output was changed from 100 W to 1 kW using a converter.The engine speed was constant at each output, and partial load operation was performed.Then, we measured the intake air volume of H 2 at each output to evaluate the performance.partial load operation was performed.Then, we measured the intake air volume of H2 at each output to evaluate the performance.

Principle of Hydrogen Generation
H2 can be produced from various resources, such as the reforming method, which extracts H2 from generated gas by burning fossil fuels, and the electrolysis method, which extracts H2 by splitting water with electricity.H2 is classified into three types, gray H2, green H2, and blue H2, depending on the manufacturing method [5].Gray and blue H2 are produced using fossil fuels, and green H2 is produced using renewable energy.Considering the global environment, the latter method is considered ideal.H2 is known to be a clean energy that does not emit CO2.However, there are issues with using it as fuel.One of the typical physical properties of hydrogen is its low density per volume.A common solution to these issues is pressurized gas and liquefied storage.These methods are not widely used due to high handling risks and costs.
We proposed an H2 onsite generation system using sodium borohydride (NaBH4) to solve the above problems.Table 3 shows the specifications of the samples and their appearances.NaBH4 is a powdery white solid crystal and is stable at normal temperature and pressure.The mass density of H2 is 10.6 wt.%, which is higher than high-pressure gas and liquified H2.NaBH4 reacts with water to generate H2 which is accelerated under certain temperature or acidic conditions.In this research, as shown in Figure 3, we used this property and adopted a production method by a chemical reaction with NaBH4 using a C6H8O7 [6].The chemical reaction formula is shown in Equation (2).

Principle of Hydrogen Generation
H 2 can be produced from various resources, such as the reforming method, which extracts H 2 from generated gas by burning fossil fuels, and the electrolysis method, which extracts H 2 by splitting water with electricity.H 2 is classified into three types, gray H 2 , green H 2 , and blue H 2 , depending on the manufacturing method [5].Gray and blue H 2 are produced using fossil fuels, and green H 2 is produced using renewable energy.Considering the global environment, the latter method is considered ideal.H 2 is known to be a clean energy that does not emit CO 2 .However, there are issues with using it as fuel.One of the typical physical properties of hydrogen is its low density per volume.A common solution to these issues is pressurized gas and liquefied storage.These methods are not widely used due to high handling risks and costs.
We proposed an H 2 onsite generation system using sodium borohydride (NaBH 4 ) to solve the above problems.Table 3 shows the specifications of the samples and their appearances.NaBH 4 is a powdery white solid crystal and is stable at normal temperature and pressure.The mass density of H 2 is 10.6 wt.%, which is higher than high-pressure gas and liquified H 2 .NaBH 4 reacts with water to generate H 2 which is accelerated under certain temperature or acidic conditions.In this research, as shown in Figure 3, we used this property and adopted a production method by a chemical reaction with NaBH 4 using a C 6 H 8 O 7 [6].The chemical reaction formula is shown in Equation (2).

Experimental Method and Conditions
Figure 4 shows the H2 generation system.In this system, NaBH4 and C6H8O7 were pumped up and reacted in a reactor to generate H2.This reaction produces boric acid and sodium citrate in addition to H2.These by-products were diverted in the flow path and sent to the waste tank.The H2 generated is at a high temperature due to the exothermic reaction and contains water vapor that must be removed.The H2 flow quantity was measured using a flow meter.Therefore, the temperature of H2 was lowered by cooling water and measured after being passed through a desiccant.The concentration of the two aqueous solutions used in the experiment was an important factor, and precipitation and sticking occurred if the concentration was not appropriate.The results of previous research [7] indicated that the NaBH4aq was 33.3 wt.% and the C6H8O7aq was 27.0 wt.%.Also, the input ratio of the aqueous solution was 5:6, and the amount was derived from the following formula.Assuming a molecular weight of 37.83 for NaBH4 and standard conditions (0 °C, 1 atm, and 22.4 L), we calculated the amount of aqueous solution required to generate H2 (25 °C, 1 atm, and 10 L). (2) shows that 4 mol of H2 is generated from 1 mol of NaBH4, and the amount of NaBH4 can be obtained from Equation (3).
From the results of Equation ( 3), the amount of NaBH4aq with a concentration of 33.3 wt.% is given by Equation (4).

Experimental Method and Conditions
Figure 4 shows the H 2 generation system.In this system, NaBH 4 and C 6 H 8 O 7 were pumped up and reacted in a reactor to generate H 2 .This reaction produces boric acid and sodium citrate in addition to H 2 .These by-products were diverted in the flow path and sent to the waste tank.The H 2 generated is at a high temperature due to the exothermic reaction and contains water vapor that must be removed.The H 2 flow quantity was measured using a flow meter.Therefore, the temperature of H 2 was lowered by cooling water and measured after being passed through a desiccant.

Experimental Method and Conditions
Figure 4 shows the H2 generation system.In this system, NaBH4 and C6H8O7 were pumped up and reacted in a reactor to generate H2.This reaction produces boric acid and sodium citrate in addition to H2.These by-products were diverted in the flow path and sent to the waste tank.The H2 generated is at a high temperature due to the exothermic reaction and contains water vapor that must be removed.The H2 flow quantity was measured using a flow meter.Therefore, the temperature of H2 was lowered by cooling water and measured after being passed through a desiccant.The concentration of the two aqueous solutions used in the experiment was an important factor, and precipitation and sticking occurred if the concentration was not appropriate.The results of previous research [7] indicated that the NaBH4aq was 33.3 wt.% and the C6H8O7aq was 27.0 wt.%.Also, the input ratio of the aqueous solution was 5:6, and the amount was derived from the following formula.Assuming a molecular weight of 37.83 for NaBH4 and standard conditions (0 °C, 1 atm, and 22.4 L), we calculated the amount of aqueous solution required to generate H2 (25 °C, 1 atm, and 10 L).Equation (2) shows that 4 mol of H2 is generated from 1 mol of NaBH4, and the amount of NaBH4 can be obtained from Equation (3).
From the results of Equation ( 3), the amount of NaBH4aq with a concentration of 33.3 wt.% is given by Equation ( 4).

Experimental Method and Conditions
Figure 4 shows the H2 generation system.In this system, NaBH4 and C6H8O7 were pumped up and reacted in a reactor to generate H2.This reaction produces boric acid and sodium citrate in addition to H2.These by-products were diverted in the flow path and sent to the waste tank.The H2 generated is at a high temperature due to the exothermic reaction and contains water vapor that must be removed.The H2 flow quantity was measured using a flow meter.Therefore, the temperature of H2 was lowered by cooling water and measured after being passed through a desiccant.The concentration of the two aqueous solutions used in the experiment was an important factor, and precipitation and sticking occurred if the concentration was not appropriate.The results of previous research [7] indicated that the NaBH4aq was 33.3 wt.% and the C6H8O7aq was 27.0 wt.%.Also, the input ratio of the aqueous solution was 5:6, and the amount was derived from the following formula.Assuming a molecular weight of 37.83 for NaBH4 and standard conditions (0 °C, 1 atm, and 22.4 L), we calculated the amount of aqueous solution required to generate H2 (25 °C, 1 atm, and 10 L).Equation (2) shows that 4 mol of H2 is generated from 1 mol of NaBH4, and the amount of NaBH4 can be obtained from Equation (3).
From the results of Equation ( 3), the amount of NaBH4aq with a concentration of 33.3 wt.% is given by Equation ( 4).flowmeter.
The concentration of the two aqueous solutions used in the experiment was an important factor, and precipitation and sticking occurred if the concentration was not appropriate.The results of previous research [7] indicated that the NaBH 4 aq was 33.3 wt.% and the C 6 H 8 O 7 aq was 27.0 wt.%.Also, the input ratio of the aqueous solution was 5:6, and the amount was derived from the following formula.Assuming a molecular weight of 37.83 for NaBH 4 and standard conditions (0 • C, 1 atm, and 22.4 L), we calculated the amount of aqueous solution required to generate H 2 (25 • C, 1 atm, and 10 L).Equation (2) shows that 4 mol of H 2 is generated from 1 mol of NaBH 4 , and the amount of NaBH 4 can be obtained from Equation (3).
From the results of Equation ( 3), the amount of NaBH 4 aq with a concentration of 33.3 wt.% is given by Equation (4).
From the results of Equation ( 5), the amount of C 6 H 8 O 7 aq with a concentration of 27.0 wt.% is given by Equation ( 6).

Influence of Intake Manifold Shape on Intake Air Volume
Figure 5 shows a comparison of intake air volume.It increased for all types to produce 600 W. When the output reached 700 W, the intake air volume decreased, and the operation became unstable.ICE used in the experiment was naturally aspirated and the air could not be adjusted.Therefore, the required air volume was obtained during high output operation.The condition with the highest value was Type1, and the intake air volume increased by about 15% compared to Type2.As a result, the straight and short intake pipe was more susceptible to the pulsation effect.Therefore, the intake air volume increased.
Since the input ratio of NaBH4 and C6H8O7 is 5:6, the amount of C6H8O7 is given by Equation ( 5).
From the results of Equation ( 5), the amount of C6H8O7aq with a concentration of 27.0 wt.% is given by Equation ( 6).

Influence of Intake Manifold Shape on Intake Air Volume
Figure 5 shows a comparison of intake air volume.It increased for all types to produce 600 W. When the output reached 700 W, the intake air volume decreased, and the operation became unstable.ICE used in the experiment was naturally aspirated and the air could not be adjusted.Therefore, the required air volume was obtained during high output operation.The condition with the highest value was Type 1, and the intake air volume increased by about 15% compared to Type 2. As a result, the straight and short intake pipe was more susceptible to the pulsation effect.Therefore, the intake air volume increased.

Influence of Intake Manifold Shape on AFR
Figure 6 shows a comparison of the AFR that is derived from the H2 flow rate and intake air volume and is expressed in Equation (7).
The theoretical AFR of the H2 ICE was 34:1, so it tended to lean burn overall.As the power increased, the AFR gradually decreased, reaching approximately 70 at 700 W for Type 1.The output did not increase as the intake air volume was greatly reduced in the high-output range.Therefore, the actual AFR fell below the theoretical AFR, and the operation became unstable.

Influence of Intake Manifold Shape on AFR
Figure 6 shows a comparison of the AFR that is derived from the H 2 flow rate and intake air volume and is expressed in Equation (7).The theoretical AFR of the H 2 ICE was 34:1, so it tended to lean burn overall.As the power increased, the AFR gradually decreased, reaching approximately 70 at 700 W for Type1.The output did not increase as the intake air volume was greatly reduced in the high-output range.Therefore, the actual AFR fell below the theoretical AFR, and the operation became unstable.The maximum thermal efficiency was 18.2% under Type 3. Compa thermal efficiency of each type, the difference was about 2%.Therefore nificant correlation between the shape of the intake manifold and the t

Measurement of Hydrogen Generation
The amount of aqueous solution required to generate 10 L/min of H as 11.6 g (NaBH4aq) and 17.2 g (C6H8O7aq) (Equations ( 5) and ( 6)).Also in a 5:6 ratio.The amount of aqueous solution varied with the voltage had to be adjusted to achieve a 5:6 ratio.We explored the relationshi and input amount prior to the performance of the pump.Table 4 show between the aqueous solution and the pump voltage required to gener of H2.The maximum thermal efficiency was 18.2% under Type3.Comparing the maximum thermal efficiency of each type, the difference was about 2%.Therefore, there was no significant correlation between the shape of the intake manifold and the thermal efficiency.

Measurement of Hydrogen Generation
The amount of aqueous solution required to generate 10 L/min of H 2 was determined as 11.6 g (NaBH 4 aq) and 17.2 g (C 6 H 8 O 7 aq) (Equations ( 5) and ( 6)).Also, it must be mixed in a 5:6 ratio.The amount of aqueous solution varied with the voltage of the pump and had to be adjusted to achieve a 5:6 ratio.We explored the relationship between voltage and input amount prior to the performance of the pump.Table 4 shows the relationship between the aqueous solution and the pump voltage required to generate 10 to 20 L/min of H 2 .
Figure 8 shows a comparison of theoretical and measured values of H 2 .The theoretical value and measured value were almost the same, and the maximum error was about 4%.This result indicated that on-site power generation by combining an H 2 generator and an H 2 engine was possible.In the future, we will experiment with the two devices.Figure 8 shows a comparison of theoretical and measured values of H2.The theoretical value and measured value were almost the same, and the maximum error was about 4%.This result indicated that on-site power generation by combining an H2 generator and an H2 engine was possible.In the future, we will experiment with the two devices.

Conclusions
In this research, the influence of the shape of the intake manifold on performance and the amount of H2 generated were researched.As a result, the following conclusions were obtained.The maximum output of the H2 electric generator was 700 W, which was less than half of the rating.It was found that the intake shape showed little effect on the thermal efficiency, and the maximum value was 18.2% for Type 3. Type 1 showed the highest intake air volume, improving by 15% compared to Type 3. The amount of H2 generated was the almost same as the theoretical value, and the maximum error was 4%.

Figure 5 .
Figure 5.Comparison of intake air volume.

Figure 5 .
Figure 5.Comparison of intake air volume.

8 Figure 6 .
Figure 6.Comparison of AFR.4.3.Influence of Intake Manifold Shape on Thermal EfficiencyFigure7shows a comparison of thermal efficiency.It is derived from output and H2 consumption and is shown in Equation (8).

Figure 7
Figure 7 shows a comparison of thermal efficiency.It is derived fr consumption and is shown in Equation (8). = 3600W BH × 100(: thermal efficiency (%); W: output (kW); B: H2 consumption (kg/h); H (kg/kJ)).The maximum thermal efficiency was 18.2% under Type 3. Compa thermal efficiency of each type, the difference was about 2%.Therefore nificant correlation between the shape of the intake manifold and the t

Figure 8 .
Figure 8.Comparison of theoretical and actual value.

Table 2 .
Dimensions of intake manifolds.

Table 2 .
Dimensions of intake manifolds.

Table 3 .
Specifications of samples.

Table 3 .
Specifications of samples.
Since the input ratio of NaBH 4 and C 6 H 8 O 7 is 5:6, the amount of C 6 H 8 O 7 is given by Equation (5).

Table 4 .
Relationship of aqueous solution and pump voltage.

Table 4 .
Relationship of aqueous solution and pump voltage.