Driving characteristics of a motorcycle fuelled with hydrogen-rich gas produced by an onboard plasma reformer

international journal of hydrogen energy 33 (2008) 7619–7629

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Driving characteristics of a motorcycle fuelled with hydrogen-rich gas produced by an onboard plasma reformer Horng Rong-Fanga,*, Wen Chih-Shenga, Liauh Chihng-Tsunga, Chao Yub, Huang Ching-Tsuenc a

Department of Mechanical Engineering, Kun Shan University, No. 949, Da-Wan Road, Yang-Kung City, Tainan County, Taiwan 710, Taiwan b Institute of Nuclear Energy Research, Atomic Energy Council, Taiwan c Fuel Cycle and Materials Administration, Atomic Energy Council, Taiwan

article info

abstract

Article history:

The driving performance and emission characteristics of a 125 cc motorcycle equipped

Received 29 July 2008

with an onboard plasma reformer for producing hydrogen-rich gas were investigated.

Received in revised form

Butane with suitable air flow rate was induced into the plasma reformer to produce

26 September 2008

hydrogen-rich gas, which was used as supplementary fuel for the internal combustion

Accepted 26 September 2008

engine. The motorcycle was run under steady and transient conditions on a chassis

Available online 14 November 2008

dynamometer to assess the driving performance and exhaust emissions. Prior to the driving, the operation parameters of the plasma reformer were optimized in

Keywords:

a series of tests and the results were an O2/C ratio of 0.55 and a butane supply rate of 1.16 L/

Plasma fuel converter

min. It was shown that under a constant speed of 40 km/h, with the CO and HC emissions

Hydrogen-rich gas

similar to that of the original engine, the NOx emission was found to be improved by 56.8%.

Driving characteristics

During transient driving condition, the improvement of 16%–41% in NOx concentration was

NOx emission

achieved by adding hydrogen-rich gas. The emissions of the motorcycle were also analyzed on a chassis dynamometer tracing an ECE-40 driving pattern. The NOx emission was improved by 34% as was the HC emission by 4.08%, although the CO emission was increased. Simultaneously, the acceleration characteristics of the vehicle were tested, and were similar under both fuelling systems. ª 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.

1.

Introduction

In the short to mid-term future, energy sources appear to still rely on traditional coal, natural gas and crude oil. This led to the development of new techniques of processing existing energy resources, such as coal cleansing, fuel cells, and fuel reforming to produce clean fuel, all of which are now gradually being recognised internationally. The current trend is to develop techniques that improve resource usage efficiency with reduced pollution.

One of the most popular methods is plasma–catalyst reforming to produce hydrogen. Horng et al. [1] demonstrated that by applying intake gas swirl, methane conversion efficiency and hydrogen concentration were both improved, and that by increasing arc frequency and the incubation period of the mixed gas in the reaction chamber, hydrogen concentration was increased. Horng et al. [2] investigated the microstructure of carbon deposit on the electrode of a methane plasma reformer using scanning electron microscopy and micro Raman and micro-PL spectroscopy. Bromberg et al. [3]

* Corresponding author. Tel.: þ886 6 2050496; fax: þ886 6 2050509. E-mail address: [email protected] (H. Rong-Fang). 0360-3199/$ – see front matter ª 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2008.09.078

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combined hydrogen-rich gas produced by a plasma converter with exhaust gas recirculation (EGR) in an internal combustion engine and demonstrated effective reduction of NOx emission as well as improvement in the HC emission. They also revealed that using a honeycombed catalyst effectively reduced the work input of the plasma and that with a low O/C ratio, both the energy conversion efficiency and hydrogen yield were improved. Peucheret et al. [4] recycled exhaust from an HCCI (Homogenous Charge Compression Ignition) engine and added methane and air for reforming with a honeycombed catalyst. By reusing heat from the exhaust and adding external heat for partial oxidation reforming, steam reforming and water-gas shifting, they investigated the effect of temperature on gas emission concentration and conversion efficiency. Tully and Heywood [5] studied lean burn of hydrogen-rich gas produced by a plasma converter in a petrol engine. They reported improvements in combustion characteristics and low fuel wastage. Under lean burn, the NOx emission was significantly reduced by 95%. Suzuki and Sakurai [6] studied the effect of adding hydrogen-rich gas on a spark ignited engine and revealed that thermal efficiency was improved by 14% when the hydrogen-rich gas was produced by a steam reformer, and by 9% when it was produced by the auto-thermal reforming process. In both cases, the NOx emission was significantly reduced. Bromberg et al. [7] investigated the effect of fuel type on the emission of an onboard hydrogen-rich gas reforming system. They noted the significance of the design of the reaction chamber on thermal management, heat lost and gas incubation period. Horng et al. [8] manufactured a small purpose designed fuel plasma converter for use on a four-stroke motorcycle. A catalyst was fitted in the exhaust pipe with the purpose of reducing polluting emission. The emission was shown to have low polluting content even during cold-start. Mohammadi et al. [9] investigated the performance of an engine with conventional fuel injected with hydrogen, and the results were the absence of knocking and backfiring. The experiments included three operating parameters, namely, ignition timing, injection timing and equivalence ratio, all of which were optimized for the engine performance in terms of good thermal efficiency, good brake mean effective pressure, and low NOx emission. Goldwitz and Heywood [10] optimized the combustion condition of a spark ignited engine under lean burning. They revealed that by adding hydrogen as supplement fuel, the limit of lean burn could be increased by more than 25%. Ma et al. [11] studied the effect of adding hydrogen to a natural gas engine on engine performance and emission. The results showed that adding hydrogen in lean burning improved engine thermal efficiency whilst reducing the CO and HC emissions. However, the process also increased the combustion temperature, leading to an increase in NOx emission. They furthered showed that by modifying the ignition timing and the MBT (Minimum advance for Best Torque), the NOx emission could be reduced to that similar to the original fuelling system. Verhelst and Sierens [12] compared the performance of hydrogen in a carbureted engine and an injection engine using a GM V8 454 spark ignition engine. The results revealed that the injection engine gave better output power and had a lower risk of backfiring. Virden et al. [13] evaluated the feasibility of using hydrogen

produced by a plasma converter as supplement fuel in an internal combustion engine. They demonstrated that overall efficiency was increased by compensating the energy lost from the reforming system by improving engine efficiency with a heat exchange unit. In view of the above research findings, the continuing energy shortage situation and the increasingly stringent emission regulations, it would appear that plasma converters may be one of the key methods in improving energy usage efficiency for use in onboard vehicles as a form of fuel supplement to internal combustion engines. In this study, canned butane was reformed into hydrogen-rich gas by an onboard plasma converter as a supplement fuel to a motorcycle engine. The major operating parameters studied were O2/C ratio and reformed butane supply rate. Simultaneously, the surface patterns of the carbon deposition in the reforming process were observed by the scanning electron microscopy (SEM) photographs; the ingredients of the deposition were analyzed by the energy dispersive spectrometer (EDS) and X-ray diffraction (XRD).

2.

Experimental set-up and methods

2.1.

Test set-up

The main apparatus was a motorcycle with an onboard plasma reformer for producing hydrogen-rich gas as supplementary fuel to its internal combustion engine. The peripheral units included a reformer, a high voltage arc generating system, reforming fuel and air supply system and gas analyzing systems. For engine performance assessment, there was a fuel intake measuring system, emission analyzing system, temperature measuring system, and a chassis dynamometer. The intake pipe of the original fuelling system was modified by teeing with two other pipes, one for directing hydrogen-rich gas into the engine and one for extra air intake. The original gasoline supply was reduced accordingly. Table 1 lists the basic specifications of the motorcycle engine. The reformer was formed by a reaction chamber and a catalyst and its specifications are shown in Table 2. The arc generating system consisted of a high voltage power supply and electrodes. The arc frequency could be as high as 10 kHz to increase the contact of fuel and air mixture, and so that the ionization and reforming could be enhanced. Sparks were generated at the electrodes by high voltage produced by a 12 VDC power supply. The anode was made of NGK-DR7E spark

Table 1 – Engine specifications. Engine type Bore Stroke Swept volume Compression ratio Compression pressure Fuel supply system Fuel

Single cylinder water-cooled four-stroke engine 52.4 mm 57.8 mm 124 cm3 9.2:1 12/570 (kg/cm2/rpm) CV type carburetor 92 unleaded petrol adding hydrogen-rich gas

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Table 2 – Catalyst specifications. Catalyst no. D  L (mm2) Pt/Pd/Rh weight ratio Loading density (g/ft3) Cell density (cell/in2)

S6550013 F35100 Pt/Pd/Rh ¼ 2:1:1 80 400

stainless steel plate, which was ground with emery papers of grade #600, #800, #1200, #1500 and # 2000 prior to each test, inserted at the catalyst inlet. The deposit was then examined under a scanning electron microscope, energy dispersive spectrometer and X-ray diffraction. For engine testing, the motorcycle was run on a chassis dynamometer at a constant vehicle speed of 40 km/h and a transient driving pattern of 0– 50–35–0 km/h. After optimizing the operating parameters of the reformer, the motorcycle was then driven at the ECE-40 urban driving pattern for assessing its exhaust emission.

plug by removing the ground electrode while the cathode was the reaction chamber body itself. Further, the catalyst with Pt/ Pd/Rh of 2:1:1 was combined with the plasma system. Table 3 lists the specifications of the arc generating system. The measuring equipment included a gas chromatographer (Agilent 6850 GC, made in US) for analyzing the gas emission, a scanning electron microscope for observing carbon deposit arising from the reforming process, a car diagnostic analyzer (ESCORT-328, made in US) and a micro-galvanometer (Prova 15, made in Taiwan) for measuring the arc frequency, voltage and current. Three K-type thermocouples were used to monitor the temperature at the front, mid and rear of the catalyst of the reformer. The analyzing systems for the driving tests included a Japanese Horiba 554JA emission analyzer, a US made CAI 600 NOx analyzer (California Analytical Instruments, made in US), a fuel flowmeter, an oscilloscope and a temperature data recorder. These were used to analyse the motorcycle emission, fuel consumption, exhaust temperature, engine oil temperature and spark plug temperature, all of which were recorder by a data acquisition system. The schematic of the test set-up is shown in Fig. 1. Fig. 2 shows the plasma-catalyst reformer and the control system installed on the tested motorcycle.

where VH2 is the dimensionless volume ratio of the hydrogenrich gas, V_ H2 is the corresponding volume flow rate, Vd is the engine displacement volume and N is the engine speed. The exhaust emission improvement is calculated from Equation (2) as follows:

F ¼ CV2

(3)

2.2.

P ¼ CV3 =htr

(4)

Experimental procedures

The experiments were separated into two parts, the first being investigating the hydrogen production performance of the plasma reforming and the other the engine performance of the motorcycle with the addition of hydrogen-rich gas. The pretests were carried out before the experiments, and the scuffing of the cylinder and the piston was found as the O2/C ratio was lower than 0.5, as shown in Fig. 3. Therefore, in the experiments, the operating parameters of the reformer included O2/C ratios of 0.50, 0.55 and 0.60, and butane intake rate of 0.89, 1.16, 1.54 and 1.99 L/min. An appropriate mixture of the fuel supply was channeled into the reaction chamber to be ionised by arcing into a plasma before entering the catalyst reformer. Here, it was mixed with oxygen to form hydrogen-rich gas, which was then collected in a bag and injected into a gas chromatographer for further analysis. Carbon deposit formed in the reforming process was collected on an 8 mm diameter

Table 3 – Specifications of arc generator.

Electric voltage (V) Electric current (A) Electric power (W) Frequency (kHz) Electric signals

Primary side

Secondary side

12 6.0 72 10 DC

3800 0.004 15.2 10 DC

2.2.1.

Relevant calculations

The normalized volume ratio of the hydrogen-rich gas is calculated from Equation (1) as follows: VH2 ¼

V_ H2   100 Vd ðN2

emimprovement ¼

emorigin

(1)

 emreformer emorigin engine

engine

engine

(2)

where emorigin engine is the emission of the original engine and emreformer engine is the emission of the engine after adding hydrogen-rich gas. The road load of the vehicle and power output of the engine are determined by the equations (3) and (4):

where F is the road load (N ) of the vehicle and P is the power output (kW) of the engine. V is vehicle speed (m/s), htr is the transmission efficiency and C is a constant for a specified vehicle derived from the coast down test. For this motorcycle, C is 0.376. Therefore, the power output of this engine for the vehicle speed of 40 km/h is 0.61 kW at 6533 rpm under the estimated 85% transmission efficiency. Other loads for any vehicle speeds could be obtained by this calculation.

2.2.2.

Measurement error analysis

The total measurement error (dk) includes a bias error (b) and a precision error (3k) such that [14] dk ¼ b þ 3k The precision error is determined by taking N repeated measurements. The precision index of the average of a set of measurements is always less than that of an individual measurement according to S Sx ¼ pffiffiffi n where S is the standard deviation of the n repeated measurements. The bias error is the systematic error considered to remain constant during a given test. The measurement uncertainty (U ) with 95 percent confidence can be given by the followed model:

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C4 H10flow meter Spark plug Air flow meter

Power supply

Plasma catalyst reformer

TC

T1-T2

C4H10

Thermocouple

Air flow meter

Tspk Emission analyzer Engine Carburetor

Gasoline

Air cleaner

Fuel flow meter

Tire

Chassis dynamometer

Data acquisition

Fig. 1 – Schematic of experimental set-up.

i12 h URSS ¼ B2 þ ðtSx Þ2 where URSS is the measurement uncertainty derived by the root sum square (RSS) method, B is the bias limit, and t is set equal to 2 for large samples (n > 30). According to the above analysis, the measurement uncertainties were estimated and shown in Table 4.

3.

Results and discussions

3.1.

Performance of plasma reformer

3.1.1.

Hydrogen production

Fig. 4 shows the emission concentration of the combustion assisting gas components (H2 þ CO) under different O2/C ratios (0.50, 0.55 and 0.60) and reformed butane flow rates. It is clear from the figure that with a butane flow rate of 0.89 L/min, the (H2 þ CO) concentration is the highest for the O2/C ratio of 0.55. For the higher butane flow rates ranging from 1.16 to 1.99 L/min, the (H2 þ CO) concentration stabilises for the O2/C ratio of 0.50 and 0.55 to a similar value. When the butane flow

rate is lower than 1.16 L/min, the emission concentration is appreciably lower for the O2/C ratio of 0.60 than the two other ratios. The reason is the more pronounced oxidation effect of the higher O2/C ratio, thereby resulting in a lower (H2 þ CO) concentration. However, with a butane flow rate of above 1.54 L/min, the emission concentration for the O2/C ratio of 0.60 is the same as the other two ratios. Fig. 5 compares the molar ratio of the combustion assisting gas components (H2 þ CO) to the combustion impeding gas components (CO2 þ N2) under different O2/C ratios and butane flow rates. It can be seen from the figure that the (H2 þ CO)/ (CO2 þ N2) ratio increases with increasing butane flow rate, with the rise more significant at the lower butane flow rates of 0.89 and 1.16 L/min. The ratio, however, begins to graduate after a flow rate of 1.54 L/min. It is evident that the molar ratio at the two lower butane flow rates is significantly lower for the O2/C ratio of 0.60, but approaches approximately 0.8 as with the two other O2/C ratios for the higher butane flow rates. In view of the effect of butane flow rate, the rate of 1.16 L/min is chosen as the setting for reforming hydrogen-rich gas for the vehicle onboard application in this study. It is noted that the O2/C ratio of 0.50 is the theoretical limit for the formation of carbon. Carbon deposit has the tendency of blocking the

Fig. 2 – Plasma–catalyst reformer and the control system on the test vehicle.

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60 Plasma-catalyst reformer

(H2+CO) concentration (%)

55 50 45 40 35

O2/C 0.50 0.55 0.60

30 25 20 15 10 5 0 0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

Butane flow rate (L/min) Fig. 4 – Emission concentration of (H2 D CO) with different O2/C ratios and reformed butane flow rates.

selected as the setting for reforming hydrogen-rich gas for the subsequent driving tests.

3.1.2.

engine at the combustion chamber causing possible scuffing of the piston and cylinder. In contrast, the higher O2/C ratio of 0.60 induces oxidation and thereby increases heat release and causes possible thermal damage of the catalyst, and high energy loss in reforming. In view of this, the compromise value appears to be the O2/C ratio of 0.55, which is therefore

Table 4 – Measurement uncertainties. Emissions GC H2 CO CO2 CH4 Emission analyzer O2 CO CO2 NOx Temperature

1.01% 0.51% 0.51% 0.50% 0.40% 0.50% 0.50% 0.65% 2.6  C

1.0 Plasma-catalyst reformer 0.9

(H2+CO) / (CO2+N2) molar ratio

Fig. 3 – Scuffing of the cylinder and scratch marks on the piston under the test setting of O2/C ratio below 0.5.

Analysis of the deposit

It is vital in the reforming process to select an appropriate O2/ C ratio. If the ratio is too high, oxidation would be excessive, leading to energy wastage. On the other hand, if the ratio is too low, carbon deposit would form, causing possible damage to engine components and even scuffing of the engine piston and cylinder. Prior to actual vehicle testing, the reformer was tested with a stainless steel plate fitted at the inlet of the catalyst to collect deposit for observation under a scanning electron microscope. In Fig. 6(a), the SEM photos represent the untested specimen. From the observations in Fig. 6(b), it is evident that for an O2/C ratio of 0.40, which is lower than the theoretical threshold of 0.5 for carbon formation of butane, the deposit is dense and the particles large, as big as 100 mm. At the theoretical threshold, it is evident that the particles are less dense and smaller but still pronounced. At higher O2/C

0.8 0.7 0.6

O2/C 0.50 0.55 0.60

0.5 0.4 0.3 0.2 0.1 0.0 0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

Butane flow rate (L/min) Fig. 5 – Molar ratio of (H2 D CO)/(CO2 D N2) under different O2/C ratios and reformed butane flow rates.

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Fig. 6 – SEM photographs of carbon deposit for different O2/C ratio (system operating time [ 30 min, reformed butane flow rate [ 1.16 L/min).

international journal of hydrogen energy 33 (2008) 7619–7629

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Fig. 7 – EDS analysis of the carbon deposit (O2/C [ 0.50).

ratios of 0.55 and 0.60, deposit precipitation is less obvious. From these and the earlier test results, it is concluded that the optimum O2/C ratio setting is 0.55. In order to determine the main ingredient of the deposit, the analysis of EDS and XRD for the deposit has been carried out, as shown in Figs. 7 and 8, respectively. From the Fig. 7, it showed that carbon (C) and ferrite (Fe) were detected. Further, the structure and phase analysis of the deposition samples were performed by using XRD simultaneously, as shown in Fig. 8. The results of the analysis also showed that the main composition of the deposit is carbon and ferrite. Where, Fe is the material of the plate for deposition collection. Hence, it could be ascertained that the carbon is the main composition of the deposition.

3.2. Cruising vehicle speed testing with hydrogen-rich gas addition Fig. 9 shows the effect of volume ratio of hydrogen-rich gas on NOx emission concentration for an O2/C ratio of 0.55 at a vehicle speed of 40 km/h. It can be seen in this figure that the NOx concentration in the initial configuration is approximately 600 ppm. With increasing intake of hydrogen-rich gas, the NOx

Intensity (a.u.)

O2/C:0.50

20

30

40

50

60

70

80

2 theta(°) Fig. 8 – X-ray analysis of the carbon deposit (O2/C [ 0.50).

concentration improves to a range of 220 ppm–340 ppm, equating to an improvement of 37.0%–57.0%. This is because of the diluting gas (CO2 and N2) components in the hydrogen-rich gas, which has the effect of impeding combustion and thereby reducing the temperature in the combustion chamber. As a result, the high temperature product NOx gas is reduced. It is clear from the figure that when the normalized hydrogen-rich gas volume ratio is 2.95%, the NOx emission shows slight increase, the reason being that described in Section 3.1.2 for Fig. 5. At this moment, the concentration of combustion assisting gas is much higher than the impeding gas, giving a comfortable mixture composition for the engine operation. As a result, combustion efficiency is improved and the NOx emission is increased, with a normalized volume ratio of 4.11%, an improvement of 56.8%. Fig. 10 compares the effect of normalized volume ratio of hydrogen-rich gas on CO, HC and O2 emissions for an O2/C ratio of 0.55 under constant vehicle speed of 40 km/h. The related equivalence ratio of the intake mixture, including gasoline and butane to air mixture, for the volume ratio of hydrogen-rich gas of 1.83%, 2.95% and 4.11% are 0.79, 0.84 and 0.92, respectively. From this figure, it is evident that the original oxygen emission is approximately 3.1%. When the normalized volume ratio of the hydrogen-rich gas is 1.83% and 2.95%, the O2 concentration is appropriate for the original engine and the hydrogen-rich gas added engines. Consequently, the CO and HC emissions are similar. Notably, the CO and HC emissions with the original engine for a vehicle speed of 40 km/h are already relatively low, therefore there is little room for improvement in this respect. When the volume ratio of the hydrogen-rich gas is 4.11%, the amount of O2 is no longer sufficient. At this moment, the O2 concentration rapidly reduces leading to incomplete combustion in the combustion chamber and a consequent increase in CO and HC emissions. The additive hydrogen-rich gas with the cylinder gas pressure of the engine was experimented for different hydrogenrich gas volume ratio, as shown in Fig. 11. These experiments were performed on the engine dynamometer under the engine speed of 3000 rpm and 3/6 throttle opening. From the comparison of the cylinder gas pressure of the engine, it could be found that the pressure rise rate for the 0% (original engine), 1.83% and 2.95% hydrogen-rich gas addition was nearly the same. However, the condition of 2.95% addition obtained the highest peak pressure. Further, in the addition of 4.11%, the

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700

80

Plasma-catalyst reformer O2/C: 0.55 Engine speed : 6533 rpm Vehicle speed : 40 km/h

NOX concentration NOX improvement

70 60

600

50 500 40 400 30 300

20

200

NOX improvement (%)

NOX concentration (ppm)

800

10

100 -0.5

0 0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

Normalized volume ratio of hydrogen-rich gas (%) Fig. 9 – Effect of volume ratio of hydrogen-rich gas on NOx emission concentration for an O2/C ratio of 0.55 and vehicle speed of 40 km/h.

5.0

4.0

CO concentration O2 concentration HC concentration

200 180 160

3.5

140

3.0

120

2.5

100

2.0

80

1.5

60

1.0

40

0.5

20

0.0

0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

HC concentration (ppm)

CO, O2 concentration (%)

4.5

O2/C: 0.55 Engine speed : 6533 rpm Vehicle speed : 40 km/h

4.5

Normalized volume ratio of hydrogen-rich gas (%) Fig. 10 – Effect of volume ratio of hydrogen-rich gas on CO, HC and O2 emission for an ratio of O2/C [ 0.55 under constant vehicle speed of 40 km/h.

30

Cylinder gas pressure (bar)

Engine speed: 3000rpm Throttle opening: 3/6 25

Normalized H2-rich gas volume ratio 0% (base) 1.83% 2.94% 4.11%

20

15

10

5

0 -180

-120

-60

0

60

120

180

240

300

360

Crank angle (degree) Fig. 11 – Cylinder gas pressure of engine with different hydrogen-rich gas volume ratio.

international journal of hydrogen energy 33 (2008) 7619–7629

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CO emission 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0

O2/C : 0.55

Reformer butane flow rate (L/min) 0.0 0.89 1.16 1.54

55

Vehicle speed target speed actual speed

Driving pattern: 0-50-35-0 km/h

50 45 40

Speed

35 30 25 20 15 10

Vehicle speed (km/h)

CO concentration (%)

a

5 0 0

20

40

60

80

-5 120

100

Time (sec) HC emission 6500 6000 5500 5000 4500 4000 3500 3000 2500 2000 1500 1000 500 0

O2/C : 0.55 Driving pattern: 0- 50-35-0 km/h

55 Vehicle speed target speed 50 actual speed 45

Reformer butane flow rate (L/min) 0.0 0.89 1.16 1.54

40 35 30

Speed

25 20 15 10

Vehicle speed (km/h)

HC concentration (ppm)

b 7500 7000

5 0 0

20

40

60

80

100

-5 120

Time (sec)

c 1000 800 700 600 500 400

Reformer butane flow rate (L/min) 0.0 0.89 1.16 1.54

Vehicle speed target speed actual speed Speed

55 50 45 40 35 30 25 20

300

15

200

10

100

5

Vehicle speed (km/h)

NOX concentration (ppm)

900

NOx emission O2/C : 0.55 Driving pattern: 0-50-35-0 km/h

0

0 0

20

40

60

80

100

-5 120

Time (sec) Fig. 12 – Emission measurements for different hydrogen-rich gas concentrations for a vehicle driving pattern of 0–50–35– 0 km/h and under a reformer O2/C ratio of 0.55 and varying reformed butane supply rate.

pressure rise rate became slower and the peak pressure also became lower than other conditions. That is, a suitable hydrogen-rich gas could cause the improvement of combustion in engine. However, if too much hydrogen-rich gas was added, it would result in poor combustion, and then poor exhaust emissions. That is, it has the best ratio of the hydrogen-rich gas addition under the compromise of assisting combustion (H2 þ CO) and impeding combustion (CO2 þ N2)

composition. The results were in agreement with those of the aforementioned exhaust emissions.

3.3. Transient driving pattern testing with hydrogenrich gas addition Fig. 12 shows the CO, HC and NOx emissions for a transient driving pattern of 0–50–35–0 km/h under different reformer

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5.0

500

O2/C: 0.55 Driving pattern: 0-50-35-0 km/h

400

4.0

300

3.0 CO concentration O2 concentration HC concentration NOX concentration

2.0

200

100

1.0 0

Table 6 – Vehicle acceleration testing (unit: second).

HC, NOX concentration (ppm)

CO, O2 concentration (%)

6.0

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0.0 -0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

Driving speed (km/h/km/h)

Original fuel system

Original fuel system with hydrogen-rich gas addition

4.4 6.6 10.4 15.4

4.4 6.8 10.4 15.2

3.6 6.2 11.2

3.4 6.4 10.8

Initial acceleration 0/50 0/60 0/70 0/80 Overtaking acceleration 40/60 40/70 40/80

Reformer butane flow rate (L/min) Fig. 13 – Emission concentration for the driving pattern of 0–50–35–0 km/h under a reformer O2/C ratio of 0.55 for varying reformed butane supply rates.

butane supply rates. The solid line is the target vehicle speed and the blank square symbol is the actual speed. Firstly, from Fig. 12(a), the CO emission is approximately 1.5% under the initial idling condition. As the vehicle accelerates, the CO concentration oscillates in a similar range, apart from the butane supply rate of 1.54 L/min. Under this condition, the CO emission rapidly increases with vehicle acceleration and appears to coarsely follow the pattern of the acceleration. The CO emission ranges from 1.5% to 4.0%. When the vehicle decelerates from 50 km/h to 35 km/h, the CO concentration shows slight increase under all reformer butane supply rates. When the throttle valve is closed at a vehicle speed of 35 km/ h, the CO emission under all butane supply rates rapidly increases to 3.0%–3.7% as the mixture gas is too rich. From Fig. 12(b), it is apparent that the HC emission is low, at approximately 100 ppm, during vehicle idling and cruising for both fuel supply systems. As with the CO emission, the HC emission rapidly increases to 4500 ppm–5000 ppm when the throttle valve is shut and the mixture gas becomes too rich. From Fig. 12(c), it is apparent that the NOx emission is low during vehicle idling, at approximately 40 ppm–70 ppm for both fuelling systems. However, as the vehicle speed increases, the NOx concentration increases to approximately 600 ppm with the original fuelling system but lower at 370 ppm with the hydrogen-rich gas addition. The NOx emission appears to reduce with increasing reformed butane

Table 5 – Emissions of the vehicle tested on the chassis dynamometer tracing the driving pattern of ECE-40.a HC (g/km) CO (g/km) NOx (g/km) Original fuel system

0.882

4.555

0.485

Original fuel system with hydrogen-rich gas addition

0.846

5.615

0.321

a Results tested based on cold-start.

supply rate, giving the lowest emission of under 170 ppm with a butane supply rate of 1.54 L/min. Fig. 13 shows the emission content for the driving pattern of 0–50–35–0 km/h under a reformer O2/C ratio of 0.55 for varying reformed butane supply rates. It is clear from the figure that adding hydrogen-rich gas has the effect of reducing the NOx emission. With the original fuelling system, the NOx emission is approximately 370 ppm. This is reduced to 300 ppm, 310 ppm and 216 ppm, an improvement of 20%, 16% and 41%, respectively, under the three butane supply rates. The original fuelling system results in a CO emission of 0.9%. With a butane supply rate of 0.89 L/min, this is reduced to 0.2%, which suggests that the mixture gas is under lean condition. The O2 emission is as high as 5.0%, leading to a high HC emission of 430 ppm, higher than that with the original fuelling system. With increasing butane supply rate, the CO emission increases but the HC emission reduces. Up to the highest butane supply rate of 1.54 L/min, the CO emission is clearly increasing whilst the reduction in the HC emission begins to graduate. After assessments on the reformer performance and the overall vehicle performance, the vehicle was tested on a chassis dynamometer tracing the ECE-40 driving pattern for assessing its emission. For this test, the O2/C was 0.55 and the reformed butane supply rate was 1.16 L/min. The results are summarized in Table 5. From the table, it can be seen that the HC emission is improved by 4.08%, NOx emission by 34% but the CO emission is increased. This increase in CO emission is due possibly to the rough transient fuel mixture ratio with the addition of hydrogen-rich gas. In other words, the transient response of the control module could be upgraded in future tests. As shown in Table 6, the acceleration performance with hydrogen-rich gas addition is similar to that with the original fuelling system.

4.

Conclusions

The driving performance and emission characteristics of a 125 cc motorcycle equipped with an onboard plasma reformer for producing hydrogen-rich gas were investigated. In the first part of the study, a butane supply rate of 0.89 L/ min–1.99 L/min combined with an O2/C ratio of between 0.40 and 0.60 has been used to produce hydrogen in the plasma reformer. Carbon deposit from the process was examined

international journal of hydrogen energy 33 (2008) 7619–7629

under a scanning electron microscope. The hydrogen-rich gas produced from the reformer was then directed into the motorcycle engine as supplement fuel. The analysis of the composition of the hydrogen-rich gas showed that an O2/C ratio of 0.50 and 0.55 resulted in similar molar ratios of combustion assisting and combustion impeding gas concentration; an O2/C ratio of 0.60 resulted in a low ratio, stabilizing at approximately 0.70. The optimum setting with the least carbon deposit and reforming energy lost was found to be an O2/C ratio of 0.55 and a butane supply rate of 1.16 L/min. This setting was applied for the vehicle driving tests. Under a constant speed of 40 km/h, with the CO and HC emissions similar to that of the original engine fuelling system, the NOx emission was found to be improved by 56.8%. During transient driving condition, the addition of hydrogenrich gas improved the NOx concentration by 16%–41%. On a chassis dynamometer tracing an ECE-40 driving pattern, the emission of the motorcycle was analyzed. The NOx emission was improved by 34% as was the HC emission by 4.08%, although the CO emission was increased. The acceleration characteristics of the vehicle, however, were similar under both fuelling systems.

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Acknowledgements The authors would like to express their appreciation to the Institute of Nuclear Energy Research, Atomic Energy Council for their sponsorship under grant 962001INER0017.

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