**3.5 The effect of the operating conditions on the reformation efficiency**

The following section discusses the variations in reformation efficiency under different operating conditions. The increase in hydrogen output and the reforming thermal efficiency were compared under the different water vapor addition, and under the use of different energy conservation approaches.

Table 3 shows the comparison of performance of the plasma fuel converter under different operating conditions, where symbol A represents the original system, i.e. the partial oxidation reforming, and B represents the autothermal reforming reaction with water vapor added. C and D use different energy conservation approaches; C represents the heat recycling approach, and D represents the heat insulation. The fuel flow rate is set at 10 L/min and the O2/C ratio at 0.8. The summary of results shown in Table 3 indicates that the best operating condition of this study is the combination of A+D, which has a maximum thermal efficiency of 77.77 %; the combination can be applied to internal combustion engines to promote energy utilization efficiency in the future. However, from the perspective of hydrogen production, the combination of A+B+D with an appropriate amount of water vapor for reaction would increase the hydrogen yield by approximately 5 %; it would also

The reforming performance for all the parameters at different equivalent power of input fuel is compared, as shown in Fig. 14. The input power of fuel directed into the reaction chamber is shown on the horizontal axis, and the output power derived from the output flow rate of H2 and CO is shown on the vertical axis. The result of this study shows that when methane is used for reforming, the output power increases linearly with the input power. The linear regression result could also serve as a convenient reference for future parameter settings for

0123456

The following section discusses the variations in reformation efficiency under different operating conditions. The increase in hydrogen output and the reforming thermal efficiency were compared under the different water vapor addition, and under the use of different

Table 3 shows the comparison of performance of the plasma fuel converter under different operating conditions, where symbol A represents the original system, i.e. the partial oxidation reforming, and B represents the autothermal reforming reaction with water vapor added. C and D use different energy conservation approaches; C represents the heat recycling approach, and D represents the heat insulation. The fuel flow rate is set at 10 L/min and the O2/C ratio at 0.8. The summary of results shown in Table 3 indicates that the best operating condition of this study is the combination of A+D, which has a maximum thermal efficiency of 77.77 %; the combination can be applied to internal combustion engines to promote energy utilization efficiency in the future. However, from the perspective of hydrogen production, the combination of A+B+D with an appropriate amount of water vapor for reaction would increase the hydrogen yield by approximately 5 %; it would also

**Input power (kW)**

0

energy conservation approaches.

1

2

3

**Output LHV power (kW) of syngas**

4

5

**R2**

6

**Methane y = 0.7183(x) - 0.2555**

 **= 0.9786**

Fig. 14. Comparison of reforming performance at different input power

**3.5 The effect of the operating conditions on the reformation efficiency** 

reforming.


A: Original system, B: ATR, C: Heat recycling, D: Heat insulation; Fuel flow rate: 10 L/min, O2/C ratio: 0.8

Table 3. Comparison of plasma converter performance under different operating conditions

increase the amount of power generated if applied to fuel cells. From this table, the variations in hydrogen and carbon monoxide yields are significantly with the combination of water gas shifting reaction, although the methane conversion efficiency is reduced. This is because the system did not adopt an external heating source to maintain its working temperature, and water addition would induce regional endothermic reactions due to the latent heat of water vaporization. The regional endothermic reaction consequently lowers the reformate gas temperature of the system and results in a reduction in the methane conversion efficiency. Another possibility for the reduction of conversion efficiency is that methanation leads to reverse reaction and increases the selectivity of methane.

This section will focus on the comparison of the theoretical calculation of the chemical equilibrium for methane reformation. The variations between the experimental results and the calculated values are compared. A comprehensive comparison of the experimental results with the theoretical calculation of the dry analysis on the output concentration of H2+CO is shown in Fig. 15; the values were measured under all of the parameters of the original system, the autothermal reforming reactions, and the energy conservative method. Linear regression analysis reveals that the R2 value for the concentration of syngas (H2+CO) is as high as 0.9179, indicating that the values obtained via experiments and the values obtained from theoretical calculation are very close.

The following section discusses the effect of plasma reforming parameters (PRP) on the overall reforming performance. The purpose is to compile all of the measured results of this study and to identify the correlations within the parameters. The reforming indicators, H2+CO concentration and thermal efficiency will be discussed. Fig. 16 shows the effect of the first plasma reforming parameters (PRP1) on the concentration of H2+CO. PRP1 is comprised of the methane molar flow rate, oxygen-carbon molar ratio, and the methane conversion efficiency; these reforming parameters are also closely associated with the concentration of H2+CO. The R2 value of the quadratic regression at different operating conditions can be as high as 0.9104. It is also shown in Fig. 16 that an increase of PRP1 signifies a greater methane flow rate, a more appropriate O2/C ratio, and a better methane conversion efficiency; and the concentration of H2+CO first increases as PRP1 increases, and then subsequently decreases. Thus, the data imply that there is an upper limit for the O2/C ratio in this system, and exceeding this limit would lead to a decrease in hydrogen concentration due to the oxidization of H2+CO into H2O and CO2 by excess oxygen.

Waste Heat Recycling for Fuel Reforming 375

Fig. 17 shows the effect of the second plasma reforming parameters (PRP2) on thermal efficiency under the operational parameter settings. The plasma reforming parameters are comprised of the methane molar flow rate, the oxygen-carbon molar ratio, the reformate gas temperature, and the conversion efficiency of methane. The effects of these plasma reforming parameters on thermal efficiency are obvious, and the R2 value of the regression calculation is as high as 0.9284. Of all the second plasma reforming parameters, PRP2 corresponds to higher thermal efficiency with higher methane flow rate, greater oxygencarbon ratio, and a higher reformate gas temperature. Under these parameters, the catalysts are able to work at an appropriate temperature, and to improve the yield of hydrogen and carbon monoxide in the reforming. As the methane conversion efficiency increases, so does the overall energy utilization efficiency; the total thermal efficiency shows a logarithmic

**Methane flow rate: 1-10 L/min**, **O2**

**Original system, Heat recycling, Heat insulation** 


**PRP=Q \* O /C\* Temp\* CH4 Conv.**

<sup>4</sup> 2 . 2 ( )( /)( )( ) *PRP n O C T CH ave conv*

The following section introduces the results of the preliminary study using hydrogen-rich gas as an auxiliary fuel for a 125 cc 4-stroke motorcycle engine. The specifications of the engine used in this experiment are shown in Table 4. Hydrogen-rich gas was supplied from different gas tanks at specific ratios; the gas mixture was directed into the engine as fuel. The performance and the pollutant emissions of the engine were measured to improve the parameters for the designing of the plasma fuel reformer in the future. Because the reformer of this study reforms gas via a partial oxidation reforming approach, the composition of the reformate gas is diverse. The typical gases in the reformate products are hydrogen, carbon

Fig. 17. The effect of the 2nd plasma reforming parameters (PRP2) on the total thermal

**3.6 A preliminary study on engine with hydrogen-rich gas as auxiliary fuel** 

**(R2**

**/C ratio: 0.5-1.0**

**y= 14.199Ln(x) + 6.3167**

**Experimental data**

 **= 0.9284)**

**Regression**

increase as PRP2 increases.

efficiency under different operating conditions

**Thermal efficiency (%)**

Fig. 15. Comparison of theoretical calculations and the experimental results of methane at different operational parameters

Fig. 16. The effect of the 1st plasma reforming parameters (PRP1) on H2+CO concentration under different operation conditions

(Including Original and energy saving systems)

**/C=0.5~1 S/C=0~2**

**Experimemtal H2**

 **flow rate:1~10L/min**

**CH4**

**O2**

0 5 10 15 20 25 30 35 40 45 50


2 . 1 ( ) ( /) ( )

0.8 0.8 0.2

Fig. 16. The effect of the 1st plasma reforming parameters (PRP1) on H2+CO concentration

*PRP n O C CH Conv* <sup>4</sup>

Fig. 15. Comparison of theoretical calculations and the experimental results of methane at

 **+ 0.8473x + 4.0104**

**Methane flow rate: 1-10 L/min**, **O2**

**R2**

**y = 1.1063x - 2.6454**

**+CO concentration (%, dry)**

**Original system, Heat recycling, Heat insulation** 

**Regression**

**Experimental data**

**/C ratio: 0.5-1.0**

 **= 0.9179**

**y= -0.0048x2**

 **= 0.9104**

different operational parameters

0

under different operation conditions

10

20

30

**H2+CO concentration (%)**

40

50

**R2**

60

**Calculated H2+CO concentration (%, dry)**

Fig. 17 shows the effect of the second plasma reforming parameters (PRP2) on thermal efficiency under the operational parameter settings. The plasma reforming parameters are comprised of the methane molar flow rate, the oxygen-carbon molar ratio, the reformate gas temperature, and the conversion efficiency of methane. The effects of these plasma reforming parameters on thermal efficiency are obvious, and the R2 value of the regression calculation is as high as 0.9284. Of all the second plasma reforming parameters, PRP2 corresponds to higher thermal efficiency with higher methane flow rate, greater oxygencarbon ratio, and a higher reformate gas temperature. Under these parameters, the catalysts are able to work at an appropriate temperature, and to improve the yield of hydrogen and carbon monoxide in the reforming. As the methane conversion efficiency increases, so does the overall energy utilization efficiency; the total thermal efficiency shows a logarithmic increase as PRP2 increases.

Fig. 17. The effect of the 2nd plasma reforming parameters (PRP2) on the total thermal efficiency under different operating conditions

#### **3.6 A preliminary study on engine with hydrogen-rich gas as auxiliary fuel**

The following section introduces the results of the preliminary study using hydrogen-rich gas as an auxiliary fuel for a 125 cc 4-stroke motorcycle engine. The specifications of the engine used in this experiment are shown in Table 4. Hydrogen-rich gas was supplied from different gas tanks at specific ratios; the gas mixture was directed into the engine as fuel. The performance and the pollutant emissions of the engine were measured to improve the parameters for the designing of the plasma fuel reformer in the future. Because the reformer of this study reforms gas via a partial oxidation reforming approach, the composition of the reformate gas is diverse. The typical gases in the reformate products are hydrogen, carbon

Waste Heat Recycling for Fuel Reforming 377

shows the engine performance, and includes thermal efficiency (shown in red), and the output horsepower (shown in blue). The right panel shows the comparison of CO (green), HC (purple), and NOx (blue) emissions. The results shown in this figure indicate that engine performance and exhaust emissions could be improved simultaneously by adding an appropriate amount of hydrogen-rich gas; that is, hydrogen-rich gas has the characteristics of assisting and impeding combustion. The output horsepower can be improved at any level of throttle opening and engine speed; in contrast to the thermal efficiency of the engine, which has better result only at low throttle opening. It could be caused by the lower ratio of [(H2+CO)/(CO2+N2)] in hydrogen-rich gas, thus resulting in the less impact on the combustion-assisting effect in other throttle openings. For the exhaust emissions of engine, although the improvement of CO and HC are not as evident as expected, NOx was greatly improved, confirming the effect of impeding combustion. Therefore, in order to produce the appropriate composition of hydrogen-rich gas for simultaneously improving the thermal efficiency and exhaust emissions of engine, the operating parameter setting of plasma

This study investigated the reformation of methane for hydrogen production by an energy conservative plasma fuel converter under different operation parameters and conditions. The experimental parameters include fuel flow rate, O2/C ratio, and S/C ratio. Additionally, the operating conditions are categorized into autothermal reforming reaction and energy conserving approaches. By conducting a series of experiments, the conclusions were drawn

For methane reforming, the reforming temperature for the best hydrogen selectivity is between 600 and 700 oC. By taking energy conservation approaches, the hydrogen production and the thermal efficiency of reformer are improved. Under the best parameter setting, the total thermal efficiency can be as high as 77.77 % with the methane flow rate of 10 NL/min and the O2/C ratio of 0.8. Furthermore, the hydrogen yield can be further increased to 86.26 % by adding an appropriate amount of water vapor (S/C ratio of 0.5), and the produced hydrogen flow rate is approximate 17.25 NL/min. And in the reforming process, the O2/C ratio, the fuel flow rate, the space velocity, and the reformate gas temperature have a great influence on reforming performance. As the first plasma reforming parameter (PRP1) increases, the H2+CO concentration shows a quadratic polynomial increase accordingly; and the thermal efficiency shows a logarithmic increase with the second plasma reforming parameters (PRP2). In this study, the HSC commercialized software was used for theoretical equilibrium calculation. The experimental results are very close to the value obtained through theoretical calculation. The regression coefficient (R2) can be as high as 0.918 between the experimented and calculated H2+CO concentrations.

This study was supported by the National Science Council Research Projects (project numbers: NSC 95-2622-E-168-008-CC3, NSC 95-2221-E-168-032-MY2 & NSC 97-2221-E-168-

converter would be very important.

**4. Conclusions** 

as followed:

**5. Acknowledgments** 

033-MY3) and Jellys Technology Inc.


Table 4. The specifications of the motorcycle engine

monoxide, carbon dioxide, and nitrogen; thus, this experiment was carried out by supplying the mixture of these four gases as added fuel.

Both H2 and CO have relatively high heating values and can be used as fuel for running engines. Additionally, hydrogen has a high flame speed, and is favorable for assisting combustion. In contrast, although CO2 and N2 do not provide heating value, they could be used for exhaust gas recirculation (EGR), and could effectively lower the combustion temperature to impede the formation of NOx. Fig. 18 shows the appropriate operating range of hydrogen-rich gas at various levels of throttle openings and engine speeds. The left panel

Fig. 18. Appropriate operating range of throttle openings and engine speeds by adding hydrogen-rich gas as an auxiliary fuel

Engine type Air cooled single cylinder 4-stroke engine

Intake valve open 0o BTDC Intake valve close 25o ABDC Exhaust valve open 33o BBDC Exhaust valve close 0o ATDC Fuel Unleaded gasoline #92 with hydrogen-rich gas

monoxide, carbon dioxide, and nitrogen; thus, this experiment was carried out by supplying

Both H2 and CO have relatively high heating values and can be used as fuel for running engines. Additionally, hydrogen has a high flame speed, and is favorable for assisting combustion. In contrast, although CO2 and N2 do not provide heating value, they could be used for exhaust gas recirculation (EGR), and could effectively lower the combustion temperature to impede the formation of NOx. Fig. 18 shows the appropriate operating range of hydrogen-rich gas at various levels of throttle openings and engine speeds. The left panel

Fig. 18. Appropriate operating range of throttle openings and engine speeds by adding

Bore 52.4 mm Stroke 57.8 mm Displacement 124 cm3 Compression ratio 9.2:1

Compression pressure 12/570 (kg/cm2/rpm) Fuel supply system CV type carburetor

Table 4. The specifications of the motorcycle engine

the mixture of these four gases as added fuel.

hydrogen-rich gas as an auxiliary fuel

shows the engine performance, and includes thermal efficiency (shown in red), and the output horsepower (shown in blue). The right panel shows the comparison of CO (green), HC (purple), and NOx (blue) emissions. The results shown in this figure indicate that engine performance and exhaust emissions could be improved simultaneously by adding an appropriate amount of hydrogen-rich gas; that is, hydrogen-rich gas has the characteristics of assisting and impeding combustion. The output horsepower can be improved at any level of throttle opening and engine speed; in contrast to the thermal efficiency of the engine, which has better result only at low throttle opening. It could be caused by the lower ratio of [(H2+CO)/(CO2+N2)] in hydrogen-rich gas, thus resulting in the less impact on the combustion-assisting effect in other throttle openings. For the exhaust emissions of engine, although the improvement of CO and HC are not as evident as expected, NOx was greatly improved, confirming the effect of impeding combustion. Therefore, in order to produce the

appropriate composition of hydrogen-rich gas for simultaneously improving the thermal efficiency and exhaust emissions of engine, the operating parameter setting of plasma converter would be very important.
