gasoline fueled SI engine

Fuel 148 (2015) 9–15

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Comparative study on measurements of formaldehyde emission of methanol/gasoline fueled SI engine Peng Geng a,b, Hui Zhang b,c, Shichun Yang d,⇑, Chunde Yao a,⇑ a

State Key Laboratory of Engines, Tianjin University, Tianjin 300072, China Merchant Marine College, Shanghai Maritime University, Shanghai 201306, China c Department of Mechanical and Aerospace Engineering, The Ohio State University, Columbus, OH 43210, USA d School of Transportation Science and Engineering, Beihang University, XueYuan Road No. 37, HaiDian District, Beijing 100191, China b

h i g h l i g h t s  The measurement methods applied to measure HCHO emission from engines were investigated.  HCHO emission from an SI engine fueled with different blending ratio was measured.  Three different methods are proposed to measure the HCHO emission from SI engines.  Interior reasons of differences on experimental results were analyzed.

a r t i c l e

i n f o

Article history: Received 9 November 2014 Received in revised form 21 January 2015 Accepted 22 January 2015 Available online 7 February 2015 Keywords: Vehicles Formaldehyde Fourier transform infra-red (FTIR) High performance liquid chromatography (HPLC) Gas chromatography (GC)

a b s t r a c t The formaldehyde emissions are harmful to human health. It is necessary to investigate and standardize the measurement methods of formaldehyde emissions from vehicles. Based on the principle of different measurements, this study proposes three different measurement methods of formaldehyde emissions from a Spark-Ignition (SI) engine fueled with 0%, 15% and 45% of methanol in volume respectively for M0, M15 and M45. Fourier transform infra-red (FTIR), high performance liquid chromatographic (HPLC) and gas chromatographic (GC) were used to measure the formaldehyde emissions from the test engine on the same engine conditions. Experimental results show that different measurement methods yield significant different results of the formaldehyde emissions, while all the measurements have the consistent trend in the change of formaldehyde emissions when the test engine operates on the different conditions. The formaldehyde emissions measured by FTIR are more than these measured by HPLC and GC, while there were slight differences on the experimental results by the use of HPLC and GC. There are three major factors leading to the different measurement results, respectively for the differences in the spectral characteristics, interferences of other exhaust emissions and the calibration of the tested gas. Compared with FTIR, chromatographic measurements present better separation of formaldehyde emissions with high frequency response, repeatability and good linearity. The formaldehyde emissions could be measured on-line by the use of FTIR, while formaldehyde emissions measured by the chromatographic measurements are absorbed into the 2,4-dinitrophenylhydrazine solution and then detected by the use of GC and HPLC offline. Therefore, HPLC and GC are preferred as the basements on the measurement of formaldehyde emissions, while FITR is preferred as an in-vehicle application. Ó 2015 Elsevier Ltd. All rights reserved.

1. Introduction As the clean and renewable alternative fuels, several kinds of alcohol fuels could reduce the regulate emissions when applied on the vehicles [1–6]. However, the use of alcohol in the vehicles ⇑ Corresponding authors. Tel.: +86 13522187088; fax: +86 22 2740 6649. E-mail addresses: [email protected] (S. Yang), [email protected] (C. Yao). http://dx.doi.org/10.1016/j.fuel.2015.01.075 0016-2361/Ó 2015 Elsevier Ltd. All rights reserved.

could also lead to the increase of unregulated emissions such as formaldehyde and acetaldehyde [7–12]. Formaldehyde was usually measured by chromatography or infra-red spectroscopy and so on [13–17]. In the previous studies, some researchers measured the formaldehyde emissions from the vehicles using the highperformance liquid chromatography (HPLC), the Fourier transform infrared spectroscopy analyzer (FTIR) and gas chromatography (GC) [18–20]. And other researchers used a small Sep-Pak pillar coating with 2,4-dinitrophenylhydrazone (DNPH) to absorb the

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P. Geng et al. / Fuel 148 (2015) 9–15

Fig. 1. Schematic of experimental system.

Table 1 Main technical specifications of tested engine. Type of the engine

4 Stroke SI

Compression ratio Cylinder volume Bore Stroke Minimum fuel consumption rate Maximum power Maximum torque

10.5 0.375 L 77.4 mm 79.5 mm 260 g/kW h 80 kW/6000/r min1 140 N m/4500/r min1

Table 2 Properties of methanol and ultralow sulfur gasoline (ULSG). Property

Methanol

ULSG

RON Density @20 °C(kg/m3) Vapor (kpa) Latent heat (kJ/kg) Sulfur content (mg/kg) Auto-ignition temperature (°C) Lower heating value (MJ/kg)

106–115 792 12.9 1110 – 437 19.7

92.8 757.6 44.0 314 8 420 44.0

carbonyl compounds in the exhaust emissions [21]. The carbonyl compounds in the exhaust emissions were eluted by the use of acetonitrile. Then these carbonyl compounds were measured by HPLC with ultraviolet (UV) detector [22]. Recently, the U.S. environmental protection agency has used the HPLC to analysis the formaldehyde emissions and other carbonyl compounds from the vehicles [23]. Moreover, formaldehyde emissions were detected by FID method. [24] In this method, formaldehyde was also collected impregnated with DNPH and converted to the 2,4-dinitrophenylhydrazone derivative. In the past years, pulsed discharge helium ionization detector (PDHID) was developed, which is a low-cost chromatographic method [25–27].With the development of oxygenated fuels, such as methanol, ethanol, Di Methyl Ether (DME), Di Methyl Carbonate, biodiesel, engine and environment scholars have focused on the unregulated emissions from the vehicles [28–30]. Therefore, it is necessary to investigate and standardize the measurement methods of formaldehyde

emissions from vehicles. Furthermore, with the development of the new technologies such as FTIR, the formaldehyde emissions could be measured online for engine bench test [31]. However, different measurement methods might lead to the differences in the experimental results of the formaldehyde emissions due to the different measurement principles. The analysis on the differences of experimental results and the internal relations on the different measurement methods are rarely reported. In this study, the formaldehyde emissions from a sparkinjection (SI) engine fueled with methanol/gasoline fuels are measured by three different measurement methods, respectively for FTIR, GC and HPLC. The FTIR named AVL SESAM FTIR was used to measure the formaldehyde emissions online, while formaldehyde emissions measured by the chromatographic measurements are absorbed into the 2,4-dinitrophenylhydrazine solution and then detected by the use of GC (SP3420) and HPLC (SY-8100) offline. The experimental results of the formaldehyde emissions are compared and the internal relations on the different measurement methods are analyzed. The differences in the spectral characteristics, interferences of other exhaust emissions and the calibration of the tested gas are the three major factors leading to the different results of formaldehyde emissions from the vehicle at the same engine load. This work is important and the standardization of measurement on the formaldehyde emissions is important for the development of methanol application in the vehicles. 2. Experimental apparatus 2.1. Test bench setup The schematic of the experimental setup is shown in Fig. 1. The engine used for this study was a four-cylinder, naturally aspirated, water-cooled, Spark-Ignition (SI) gasoline engine, with Table 3 Effect on HCHO by the flow rate of the sampling. Flow rate (L/min)

HCHO/(106)

0.12 0.15 0.20

24 19 15

P. Geng et al. / Fuel 148 (2015) 9–15

specifications shown in Table 1. The test engine was coupled with an eddy-current dynamometer, and the speed and torque of the gasoline engine were controlled by the Xiang Yi engine test system that allows adjustment of engine load at a fixed engine speed or adjustment of engine speed at a fixed engine load. The fuels used include CHN V gasoline fuel with less than 10-ppm by weight of sulfur and industrial grade methanol. Main properties of the test fuels are shown in Table 2. In all cases, fuel consumptions were measured gravimetrically using an electronic balance with a precision of 0.1 g. The experiments were carried out with 0%, 15% and 45% by volume of methanol blended with gasoline respectively for M0, M15 and M45. It was found that methanol can be mixed with gasoline in any proportion without using additives, and no phase separation was observed when a sample of the mixed fuel was sealed and then the mixed fuel was kept at room temperature for one week. 2.2. Principle of the three measurement methods 2.2.1. Principle of Fourier transform infra-red (FTIR) The principle of AVL’SESAM FTIR system is shown as follow [32]: after absorbing the energy, the molecular vibrations of the substance lead to the energy level transitions. Then the process was recorded and the infrared absorption spectrum of the molecular was measured. Because the gas molecular absorbs part of the infrared light, the light intensity was declined from Io to I when the infrared light went through the test gas. The extent of absorption of the gas molecular (Absorbance) A was defined like this: A = log (Io/I), where Io is the original light intensity, and I is the intensity after being absorbed. The quantitative theory of the Infrared spectroscopy was based on Beer–Lambert Law: the absorbance of the gas A was proportional to the gas concentration c and the length when the light go through the test gas b. Beer–Lambert Law can be expressed as A = kbc, where k is the absorption coefficient. As long as we know the value of k and b, then we can calculate the value of c. The formaldehyde is measured through two wavelengths with their eigenvalues of 2779 and 2781.5/cm. The infrared beam reaches the sample pool through a 2 km muti-level reflection optical path. The detection limit of this method is 4  109. 2.2.2. Principle of high-performance liquid chromatography (HPLC) In this study, the formaldehyde emissions are measured by HPLC (SY-8100) with the ultraviolet absorption detector [33]. It is based on the principle of solute molecules absorbing the ultraviolet light. When a bunch of monochromatic light go through the flow cell, the degree of absorption is proportional to the concentration of the light-absorbing component and the optical path length of the flow cell L if the mobile phase does not absorb the light. The

.mL

250 200

HCHO/

150

11

light transmittance could be measured by using physical method, and then the absorption could be obtained by calculating the negative logarithm.

e¼1

IðkÞ ¼ 1  expðrðkÞnlÞ IiðkÞ

ð1Þ

The gas absorption cross section for ultraviolet light r can be expressed as:

r ¼  ln



   IðkÞ  IdðkÞ PT0 n n0 l IiðkÞ  IdðkÞ P0T

ð2Þ

I represents the strength of the transmitted light and Io represent the strength of the incident light; k is the wave length with its unit nm; r(k) is the absorption cross with its unit cm; n is the number of molecules per unit volume of the gas with its unit molecules cm3, 1 is the optical path of the gas sample chamber. The effect of the background light impurities should be excluded when measured, i.e. get the background signal Id when shut down the deuterium lamp. no the number of molecules per 1 cm3 at the standard condition, the value is 2.687  1019 molecular/cm3. 2.2.3. Principle of gas chromatographic (GC) The formaldehyde emissions from vehicles were measured by the method of DNPH–GC–FID with the flame ionization detector (FID) [34]. The main component of the FID is an ion chamber made by stainless steel. The ion chamber is made up of collector electrode, polarization electrode (emitter electrode), gas inlet and flame-thrower nozzle. At the low part of the ion chamber, hydrogen and carrier gas will go through the nozzle after mixing. Then the mixture will be ignited after mixing with oxygen. The ions between the two electrodes are very few when there are no samples. Once the organic matter was measured, the ionize reactions will work and then many ions were formed. In the FID, the hydrocarbon will split into CH, CH2and the two radicals will react with O2 and then generate the CHO+, CH2OH+, COOH+, C2OOH+, COO+, CHO2 and electron. The steam and the CHO+ will collide and form the H3O+, for example:

CH þ O ! CHOþ þ e CHO þ þH2 O ! CO þ H3 Oþ where e represents an electron. Under the action of the electrostatic field formed by collector electrode and the polarization electrode, the positive ions such as CHO+ and H3O+ move toward the collector electrode, and the electron will move toward the polarization electrode. The ion flow will form the measurable chromatographic signal after the process of impedance transformation and amplifier amplification (107–1010). The ion number produced by the detector is related to the mass of the carbon atom. So the hydrogen flame detector is one kind of mass detectors. This kind of detector has response to most organic matter. Its sensitivity is higher than the thermal conductivity detector and can be used to analysis the trace amounts of the organic matter. However, it is not able to be used to detect the inert gases, the inorganic gas and the carbonyl in the organic matter. 2.3. System analysis and calibration

100 50 0

0

50000

100000

150000

200000

250000

peak area/ (uV.s) Fig. 2. Standard curve equation: y = ax + b; a = 1.06E003, b = 6.00E001, R = 0.9998.

2.3.1. Calibration of FTIR The calibration method can be described as follow: the standard substances go through the gas pool driven by the carrier gas, and the total mass of the standard substance is known. Then the standard sample was applied, and the procedure is shown as follows: firstly, the standard sample go through the nitrogen pool in at least 5 min; Secondly, the background spectra is collected at the nitrogen atmosphere; Thirdly, all of the standard samples are injected

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P. Geng et al. / Fuel 148 (2015) 9–15

(a) Chromatograms with GC

(b) Chromatograms with HPLC

Fig. 3. Chromatograms with GC and HPLC.

by the use of the nitrogen as the carrier gas to go through the gas pool; Finally, the sampling was executed continuously for the whole process and then the infrared absorption spectra could be measured at any time. 2.3.2. Collection and preparing the specimen of the chromatography and standard curve 2.3.2.1. Collection and preparing on the specimen. The specimen collection: there are two porous glass plate absorption tubes in series to collect the formaldehyde in the exhaust gas [35–37]. The concentration of the formaldehyde under the same working condition with different sampling flow rate is shown in Table 3. The result shows that the absorption characteristic was well when the sampling flow rate is low. The final sampling flow rate is decided as 0,12 L/min. In order to decrease the error, the soap film flow-meter is used to measure the flow rate at the beginning, middle and end of the sampling process. Then take the averaged value of the three numbers. The sampling time is 20–40 mins. The specimen preparation: The sample will be transferred to a 50 mL volumetric flask after being collected. Then the 10 mL absorbent is divided into three parts to wash the in-wall of the absorption tube. The scrubbing solution is also poured into the volumetric flask. Then 2 mL carbon disulfide was added to the volumetric flask using the transfer pipette. The volumetric flask was shocked for 3 min, then the liquid was transferred to the 60 mL separating funnel. The lower extract liquor was collected into a 10 mL colorimetric tube after dehydration. When processing the chromatographic analysis, the formaldehyde was measured three times under every working condition. The error of the detection result is less than 5%. 2.3.2.2. Chromatographic conditions. The chromatographic column of the liquid chromatography is the ODS2C18 chromatographic column (4.6 mm@250 mm), and its temperature is 35 °C. The flow velocity is 1.0 ml/min and the mobile phase is 60:40 (methanol:deionized water). Moreover, the time of analysis is 15 min, and the wave length and injection volume are 254 mm and 60 lL, respectively. The detector of the gas chromatography is hydrogen flame ionization detector (FID) and the chromatographic column is stationary phase 1.5% OV-101/C.W.D (80–100), 2 m ⁄ 6 mm packed glass column. The temperatures of the column, vaporizing chamber and detector are 180 °C, 270 °C and 270 °C, respectively. The flow velocity of the carrier gas is 30 mL/min for N2 and H2 and 300 mL/ min for air. The air inflow is 5 lL. 2.3.2.3. Drawing the standard curve. The standard liquid was diluted with the absorption liquid in the 50 mL measuring flask to

compound the standard solution series with the content of formaldehyde around 25–500 mg. The number of concentration point is six. The standard liquid was extracted with the carbon disulfide after stewing for 2 h. This process is repeated for three times at every concentration point to keep the time qualitative. The external standard method of area is used to quantity. The concentration of formaldehyde (lg/mL) is determined as ordinate, and the mean of the peak area is determined as abscissa. The standard curve is drew as Fig. 2. The equation of the standard curve is y = ax + b; a = 1.06 ⁄ 103, b = 600 and the coefficient of determination is R2 = 0.9995. Fig. 3(a) and (b) shows the chromatogram of the formaldehyde detection from gas chromatography and the highperformance liquid chromatography. The figures show that the hydrazone peaks of the formaldehyde is obvious and there are no interferences from miscellaneous peaks. The peak time is constant and the degree of separation is good. Moreover, the sensitivity is quite high. 3. Results and analysis Fig. 4 shows the experimental results of formaldehyde emissions from the vehicle measured by FTIR, GC and HPLC before the three-way-catalyst. As shown in Fig. 4, there is a significant decrease of formaldehyde emission with the engine load from low to medium, while increase with the engine load from medium to high. When operating at the speed of 2000 r/min and 3600 r/min, formaldehyde emissions measured by FTIR are more than those measured by GC and HPLC, while there were slight differences on the experimental results by the use of HPLC and GC. There are three major factors leading to the differences of the experimental results of formaldehyde emissions measured by different methods. Firstly, the theories of measurements are different. Although both FTIR and the UV are based on the Beer– Lambert Law, infrared optical and the ultraviolet properties of the gas are different. Moreover, due to the extent of absorption of the gas to infrared optical and the ultraviolet is related to the temperature and pressure of the gas, different detection temperature and pressure of FTIR and UV would lead to different level of infrared optical and the ultraviolet. Though the principle of the gas chromatography and the liquid chromatography are different, they are all highly selective to their test substance, so their detection results have little difference. Secondly, there is the interference from other ingredients in the exhaust. Since formaldehyde is easily soluble into the water and the infrared spectroscopy of the formaldehyde and H2O is overlapped, as shown in Fig. 5. Thus the water content in the exhaust gas has an effect on the quantification of formaldehyde concentration.

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P. Geng et al. / Fuel 148 (2015) 9–15 50 45

50 2000r/min, before TWC, M0

45

FTIR HPLC

40

HCHO/10 -6

HCHO/10 -6

25 20

20 15 10

5

5 0.2

0.4

0.6

0.8

0

1.0

0.6

0.8

1.0

(a) 2000r/min, before TWC, M0

(b) 3600r/min, before TWC, M0 70

FTIR

2000r/min, before TWC, M15

HPLC

60

GC

FTIR

3600r/min, before TWC, M15

HPLC GC

HCHO/10 -6

50

30

40 30

20

20

10

10

0.2

0.4

0.6

0.8

0

1.0

0.2

0.4

0.6

0.8

IMEP/MPa

IMEP/MPa

(c) 2000r/min, before TWC ,M15

(d) 3600r/min, before TWC, M15 120

120 2000r/min, before TWC, M45

3600r/min, before TWC, M45

FTIR HPLC GC

100

1.0

FTIR HPLC GC

80

HCHO/10 -6

80 60

60

40

40

20

20

0

0.4

IMEP/MPa

40

100

0.2

IMEP/MPa

50

HCHO/10 -6

25

10

70

HCHO/10 -6

30

15

0

GC

35

30

60

HPLC

40

GC

35

0

FTIR

3600r/min, before TWC, M0

0.2

0.4

0.6

0.8

1.0

0

0.2

0.4

0.6

0.8

IMEP/MPa

IMEP/MPa

(e) 2000r/min, before TWC, M45

(f) 3600r/min, before TWC, M45

1.0

Fig. 4. Formaldehyde emission from M0, M15 and M50 fueled SI engine in three measurement systems.

Moreover, in 200 K–400 K, the infrared band of formaldehyde gas narrows down with the increase in temperature. The whole-line width of the infrared spectrogram increases, and it could affect the detection accuracy and made the detection more susceptible. The detection substance of the gas chromatography and the liquid chromatography is 2,4-dinitrophenylhydrazone, which is the derivant of the aldehyde ketone substance absorbed by the acid saturated liquid of the 2,4-dinitrophenylhydrazine. Its detection accuracy is not so high, but its immunity to the impurities in the exhaust is strong. Finally, there are different instrument

calibrations with each measurement. The gas chromatography and the liquid chromatography are calibrated by the standard curve, and there is high accuracy and linearity, normally the linearity is more than 0.999. Moreover, the instruments are always calibrated before detection, so they have great reliability. The calibration of the FTIR is done before leaving factory, but only standard curve could be calibrated before engine test. However the formaldehyde emission is not included in the standard curves, thus the measured value for unregulated emission could be deviated when only standard calibration is performed.

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P. Geng et al. / Fuel 148 (2015) 9–15

(a) Infrared spectrogram of H2O

(b) Infrared spectrogram of HCHO

Fig. 5. Infrared spectrogram of H2O and HCHO.

4. Conclusions Experiments were conducted on an electronically controlled multi-point port injection SI engine operating on CHN V fuel blended gasoline with methanol at 0%, 15% and 45% volume. There were three different methods applied to measure formaldehyde emissions, which were Fourier transform infra-red (FTIR), high performance liquid chromatographic (HPLC) and gas chromatographic (GC). The following conclusions can be drawn from this study. 1. When operating on the same engine condition, there are significant differences on the formaldehyde emissions with three measurements. Formaldehyde emissions measured by FTIR are more than those from GC and HPLC, while the results from GC and HPLC are nearly the same with each other at all cases. 2. There are three reasons leading to the difference on the formaldehyde emissions measured by these three measurements. Firstly, the measuring theories of these three measurements are different, and the temperature and pressure have an effect on the accuracy of each measurement. Secondly, there are the interferences from other ingredients in the exhaust. Finally, there are different instruments calibrations with each measurement. 3. When operating on pure gasoline fuel mode and methanol/gasoline blended fuel mode, there is a significant decrease in formaldehyde emission with the engine load from low to medium, while increase from medium to high engine conditions. 4. There is a significant increase of formaldehyde emissions from the vehicle with the increase of the methanol content in the test fuels.

[3]

[4]

[5]

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[8]

[9]

[10]

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[12]

[13]

[14]

[15]

Acknowledgements [16]

The authors wish to thank for the National Natural Science Foundation of China (No. 51176135) and National High-tech R&D Program (863 Program) (No. 2012AA111719) of the Ministry of Sci. & Tech. of China.

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