15 2016

Accepted Manuscript A comparison of performance and exhaust emissions with different valve lift profiles between gasoline and LPG fuels in a si engine Can Çinar, Fatih Şahin, Özer Can, Ahmet Uyumaz PII: DOI: Reference:

S1359-4311(16)31160-7 http://dx.doi.org/10.1016/j.applthermaleng.2016.07.031 ATE 8629

To appear in:

Applied Thermal Engineering

Received Date: Revised Date: Accepted Date:

16 June 2016 2 July 2016 4 July 2016

Please cite this article as: C. Çinar, F. Şahin, O. Can, A. Uyumaz, A comparison of performance and exhaust emissions with different valve lift profiles between gasoline and LPG fuels in a si engine, Applied Thermal Engineering (2016), doi: http://dx.doi.org/10.1016/j.applthermaleng.2016.07.031

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A COMPARISON OF PERFORMANCE AND EXHAUST EMISSIONS WITH DIFFERENT VALVE LIFT PROFILES BETWEEN GASOLINE AND LPG FUELS IN A SI ENGINE Can ÇINAR1, Fatih ŞAHİN1, Özer CAN2, Ahmet UYUMAZ3 1

Department of Automotive Engineering, Faculty of Technology, Gazi Unversity., 06500, Beşevler, Ankara, Turkey 2

Department of Automotive Engineering, Faculty of Technology, Pamukkale University, 20020 Kınıklı, Denizli, Turkey 3

Department of Automotive Technology, Vocational High School of Technology and Science, Mehmet Akif Ersoy University, 15100, Burdur, Turkey

ABSTRACT In this study, a single-cylinder, four-stroke, single overhead camshaft (SOHC), spark ignition (SI) gasoline engine was converted to run with liquefied petroleum gas (LPG) fuel. To improve the volumetric efficiency, the camshaft of the engine was re-designed using classical spline method for different valve lifts. The variations of engine brake torque, power, brake specific fuel consumption (BSFC), HC, CO, CO2 and NOx emissions and exhaust gas temperature were investigated with unleaded gasoline and LPG fuels for different valve lifts. The experiments were conducted at 1700-3200 rpm engine speeds range at wide open throttle (WOT) and λ=1. Engine torque and power decreased and BSFC increased with LPG fuel for the 7 mm valve lift. Brake engine torque decreased by 8.82 % and BSFC increased by 7.25 % with LPG fuel compared to gasoline for 7 mm valve lift at 2600 rpm engine speed. However, HC and CO emissions decreased, NOx emissions increased with the usage of LPG fuel. HC and CO emissions decreased by 18.24 % and 5.3 %, respectively, and NO x emissions increased by 7.67 %, with LPG fuel at 2600 rpm engine speed. An improvement was observed on engine torque, BSFC, HC and CO emissions with the increase of the valve lift to 8 mm and LPG fuel. At the low engine speeds, engine performance and exhaust emissions deteriorated with the increase of valve lift for gasoline fuel, while improvements were found at middle and higher engine speeds.

Keywords: LPG, Gasoline, Valve lift, SI engine, Engine performance, Exhaust Emissions

1

1. INTRODUCTION Liquefied petrol gas (LPG) and compressed petrol gas (CNG) have received considerable attention due to environmental pollution and rise in oil prices in recent years. LPG remarkably reduces harmful exhaust emissions from motor vehicles [1]. One significant reason to choose alternative fuel is to be used in internal combustion engines (ICE) without detailed modifications. LPG is also available and economic fuel. Moreover, LPG is an attractive alternative fuel as it has higher octane number and lower exhaust emissions according to other fuels [1-6]. Compression ratio and thermal efficiency could be increased, because LPG has high octane number in gasoline engines. LPG has also higher hyrogen-carbon ratio. Liquefied fuel shows cooling effects during phase changing. However, LPG prevents cooling effect [7-12]. It can be also mentioned that LPG has good storage safety at low pressures [13,14]. But, power output decreases when LPG was used in ICE due to lower volumetric efficiency. This is the most important difficulty that must be overcome when LPG is used in ICE. At this point, volumetric efficiency can be improved via using different valve lift mechanism. Higher valve lift will help to take more charge mixture into the cylinder resulting in higher power output when LPG was used as test fuel. Experimental studies have beed carried out to understand the effects of LPG in ICE. Sayın et al. [1] investigated the effects of dual fuel (gasoline+LPG) on engine performance and emissions in a spark ignition engine. They have determined that SFC reduced 4 % and CO and particulate matter emissions similarly decreased 13 % and 5 % respectively. Gümüş et al. [2] developed a program calculating the variations of combustion products volumetrically due to utilization of natural gas in an engine fueled with natural gas and diesel. They have observed a reduction on volumetric fraction of CO2, CO, N2, SO2 and O2 combustion products. Gümüş [3] researched the effects of LPG on performance and emissions in a spark ignition engine. The improvements were observed on exhaust emissions and fuel economy with LPG compared to gasoline. Murillo et al. [15] obtained important reductions on HC, CO emissions and SFC without decreasing on brake power with LPG compared to gasoline in a spark ignition engine. But NOx emissions increased. Kim and Bae [16] have seen that engine efficiency increased while NOx and CO2 emissions decreased at higher compression ratios with leaner charge mixture. Akbaş et al. [17] investigated the effects of LPG on SFC consumption and brake power in a spark ignition engine increasing compression ratio. Fuel consumption decreased 12 % and brake power increased 7 % when compression ratio was increased from 9.5 to 13. Çelik and Balki [18] showed that LPG increased engine performance and reduced emissions in low-power engines when the engine was operated at higher compression ratio. İçingür and Dost [19] experimented the four different test fuel including propane and butane 2

in order to see the effects on performance and emissions. Engine brake torque and brake power decreased 3.6-7 % compared to gasoline. CO and HC emissions decreased 42-62 % and 37-45 % respectively. Kihyung and Ryu [20] investigated the flame formation and combustion characteristics of LPG experimentally. They have seen that combustion stability was deteriorated at leaner mixtures. Sayın et al. [21] investigated the variation of combustion products using a chemical combustion computer program prepared by Olikara and Borman [22]. They have seen that exhaust emissions can be reduced remarkably with dual fuel operation. Ciniviz and Salman [23] investigated the effects of diesel and LPG on engine performance and emissions at full load and six different engine speed. Brake torque and power increased by about 5.8 % with dual fuel compared to single fuel. Furthermore, the improvements were seen on NO x and soot emissions compared to single fuel. Latusek et al. [24] compared the emissions of LPG and gasoline in two and four stroke engines. HC and NO x emissions decreased 19.6 %, 27.4 % for CO emissions. Polat et al. [25] operated the four stroke, four cylinder engine with LPG and investigated the performance and emissions. CO and HC emissions decreased with LPG according to gasoline. Bayraktar et al. [26] analyzed the effects of LPG theoretically in a spark ignition engine. They observed that CO and NO mole fractions were lower compared to gasoline. Yeom et al. [27] investigated the effects of LPG and gasoline in HCCI engine equipped with variable valve mechanism. They have seen that HC and CO increased when intake valve timing was retarded. Saleh [28] aimed to determine the effects of LPG on performance and exhaust emissions in a two cylinder, naturally aspirated, four stroke diesel engine. It was found that NO x emissions decreased as the fraction of butane increased in the test fuel. Ceviz et al. [7] investigated the effects of LPG temperature on performance and exhaust emission experimentally. They showed that NO emissions can be decreased 2 %. Elnajjar et al. [29] invesigated the effects of LPG fuel including different propane to butane volume ratio. The test results indicated that different LPG composition has a slight effect on engine efficiency. In contrast, combustion noise increased remarkably. Erkus et al. [30] experimented the electronically controlled LPG injection system in a four stroke carburettor SI engine. They also compared the LPG injection system with different fuel and mixing systems. It was shown that LPG injection system can achieve higher power output, lower specific fuel consumption and exhaust emissions. Lower volumetric efficiency is very important handicap with LPG in SI engine. For this reason, different valve mechanism could be applied for better volumetric efficiency in SI engine. Thus, different cam profile design methods are used such as spline curves [31-36]. Sarıdemir [32] studied the different methods for designing cam profiles. He designed new cam profiles using 5th classical spline methods for two cylinder ICE and investigated the characteristics of modified cam profiles such as displacement, velocity, 3

acceleration and jerk. Karabulut and Sarıdemir [35] researched the displacement, velocity, acceleration and jerk values of different cam profiles. For this purpose, they obtained cam profiles using 5th order classical spline method including 6, 7 and 8 mm valve lift. It was concluded that better cam profile was obtained with the increase of lifted-valve period. They have emphasized that engine performance and volumetric efficiency were decreased as velocity, acceleration and jerk values were increased. They have also stated that valve lift, pressure angle and lifted-valve period should be considered in a detail for ideal cam profiles.

In this study, LPG fuel kit was mounted in a single cylinder spark ignition engine. Valve lifts were altered in order to take more charge mixture into the cylinder and increase effective compression ratio. Volumetric efficiency decreased when LPG is used in SI engine resulting in lower power output. One of the most attractive methods is to change valve mechanism in order to improve volumetric efficiency. The aim of this study is to determine the effects of valve lift in a SI engine fueled with LPG and gasoline on engine performance and exhaust emissions. For this purpose, the test engine was experimented at WOT and different engine speeds ranging from 1700 to 3200 rpm at stoichiometric air/fuel ratio.

2. EXPERIMENTAL APPARATUS AND PROCEDURES In this study, single-cylinder, four-stroke, single overhead camshaft (SOHC), SI engine was used in the engine tests. The specifications of the test engine are given in Table 1.

Table 1. The specifications of the test engine

Fuel conversion of the test engine was carried out with mixer type LPG system which supplies LPG gas with a vaporizer to the upstream of inlet air in the throttle body of carburetor. The test engine was coupled with an electrical dynamometer on a Cussons P8160 type engine test bed. The electrical dynamometer is a swinging field DC rated for 10 kW power absorption at 4000 rpm maximum machine operating speed. The dynamometer has a microprocessor controlled regenerative thyristor driver for load and closed-loop speed control which is also capable of motoring. The engine load was measured with strain gauge load cell sensor. The engine speed was measured with a toothed wheel on the dynamometer shaft by magnetic pick-up sensor. The exhaust gas measurements were performed with a SUN MGA 1500 model exhaust gas analyzer. The overall layout of the experimental set up is seen in Figure 1. 4

Figure 1. The overall layout of the experimental set up Technical specifications of the analyzer which can measure CO, HC, NOx, O2, CO2 and λ values for both of gasoline and LPG fuels are given in Table 2. LPG and gasoline were used in the experiments as the test fuels. The chemical properties of the test fuels are given in Table 3.

Table 2. The technical specifications of the exhaust gas analyzer

Table 3. The chemical properties of the test fuels [37,38]

Gas sampling probe was located 150 mm downstream of the exhaust port. Temperatures of the inlet air, exhaust gas, lubricating oil were measured via Newtronic 97 multi-channel electronic temperature indicator. The thermocouples used were NiCr-Ni type, which can measure up to 1200 °C. Exhaust thermocouple was located 80 mm far from the exhaust port. The fuel flow rates for gasoline and LPG were measured with a high-precision electronic balance. Air flow rate of the test engine was measured with laminar flow element (Meriam Z50MC2-4F model) and Merriam LFS-1 mass flow computer. The overall layout of the experimental set up is shown in Figure1. The engine tests were conducted at λ=1 and WOT conditions with different engine speeds ranging from 1700 to 3200 rpm in intervals of 300 rpm. The experiments were completed with two different (7 mm and 8 mm) valve lifts for gasoline and LPG fuels. Before each test, the engine was warmed up with gasoline fuel. Engine oil temperatures were kept stable around 80°C. Each test was repeated 3 times under the steady-state conditions and the results were averaged to decrease the uncertainty.

2.1. Re-Designing of Cam Profiles for Different Valve Lifts Classical 5th-order spline approximation was used in the re-designing of cam profiles for different valve lifts [19-21, 32, 35]. Re-designed cam profiles have a 30 mm basic circle diameter and 136° cam angle with different valve lifts as 6.5, 7, 7.5 and 8 mm, respectively. Basic circle diameter and cam angle are the standard values in the calculating of the cam profiles which are measured from the test engine camshaft. Suitable valve lift, opening valve periods depend on cam designing method. Furthermore, smooth and efficient operation of valve mechanism can be ensured using proper cam profile design method. Çınar and Uyumaz [39] reported that the feature of single point contact of cam into follower has been lost with the increase of valve lift using 5 th degree classical 5

spline method. Re-designing of cam profiles with different valve lifts was calculated by using the following classical spline function with finite time difference,   x    x    x    x    x  s   a   b   c   d   e  f  tx   tx   tx   tx   tx  5

4

3

2

x    t 

where “θ” is the cam angle, “x” and “t” are the start and ends timings of the function in terms of θ values. In the analyses, valve opening timings were divided into periods when determining the nodes. As a result of the analyses, images of re-designed cam profiles were transferred to the CAD environment and cams were manufactured from AISI-SAE 4140 steel by CNC wire erosion machining (Figure 2). Then, heat-treatment process was applied to 60 HRc hardness. Cam shaftcam hub connections were provided with M20x1 screw-type teeth. Desired cam profile can be removed or mounted to the engine cam shaft. The cam lift can be adjusted and secured with in position by each with two lock-nut.

Figure 2. Images of manufactured cam profiles

As it is shown in Figure 3, displacements of the cam profiles are obtained for different valve lifts (6.5, 7, 7.5 and 8 mm) and each period. Velocity and acceleration curves of re-designed cams are shown for 2000 rpm in Figure 4 and Figure 5, respectively. Velocity curves of re-designed cams for different valve lifts were calculated by taking the first-order derivative of the displacement with respect to cam angle. Also, acceleration profiles of re-designed cams for different valve lifts were determined by using second-order derivative of the displacement with respect to cam angle. As it is seen from Figure 3, maximum velocities depending on the valve lifts increased for the same opening valve periods. Maximum velocity is 1967 mm/s for 6.5 mm valve lift, while it was obtained as 2486 mm/s when the valve lift was increased to 8 mm. Also, maximum acceleration is 1.075x106 mm/s2 for 6.5 mm valve lift, while it was obtained as 1.783x106 mm/s2 when the valve lift was increased to 8 mm. From the results, it is understood that the maximum values of velocity profiles increase with the increase of the valve lifts. Consequently, the maximum values of acceleration profiles related with velocity profiles were also showed increments depending on the increase of the valve lifts.

Figure 3. Displacement curves of the cam profiles

Figure 4. Velocity curves of cam profiles 6

Figure 5. Acceleration curves of cam profiles 2. RESULTS AND DISCUSSIONS Figure 6 illustrates the effect of two different valve lift (7 and 8 mm) on the engine brake torque between 1700-3200 rpm engine speeds for unleaded gasoline and LPG fuels. Maximum engine brake torque with 7 mm valve lift was obtained as 19.05 Nm at 2600 rpm for gasoline fuel. Also, decrease on the engine brake torque up to 8.82 % was observed when the engine fueled with LPG fuel and it was obtained as 17.37 Nm at 2600 rpm. Moreover, improvements on the air-fuel flow into the cylinder by increasing the valve lift to 8 mm resulted in improvements on the engine brake torque at higher than 2000 rpm when the engine fueled with LPG fuel. Maximum increase on the engine brake torque for 8 mm valve lift and LPG fuel was found to be 7.44 % at 3200 rpm. On the other hand, engine brake torque with gasoline fuel deteriorated at especially low engine speeds when the valve lift increased to 8 mm. As seen from Figure 6, the engine brake torque was found to be 5.66 % lower at 1700 rpm engine speed for 8 mm valve lift. It is possible to say that this result caused by forcing back a portion of air-fuel mixture from the piston movement towards to the TDC.

Figure 6. The variations of engine brake torque versus engine speed with LPG and gasoline

The variation of volumetric efficiency between 1700-3200 rpm engine speeds is shown for two different valve lift (7 and 8 mm) with unleaded gasoline and LPG fuels as seen in Figure 7. As it is seen that the volumetric efficiency generally decreased with LPG fuel when the compared with gasoline fuel. Maximum volumetric efficiency was obtained as 60.99 % with gasoline fuel at 2600 rpm in case the engine was run with 8 mm valve lift. It was stated that volumetric efficiency improved with the increase of valve lift in case LPG was used. Volumetric efficiency increased by about 1.48 % with 8 mm valve lift compared that 7 mm valve lift at 2600 rpm engine speed. It can be also mentioned that volumetric efficiency with LPG gets closer to the volumetric efficiency obtained by gasoline in case 8 mm valve lift was used. The superior gasoline performance is thought to be primarily due to the charge cooling effects associated with evaporation of gasoline during intake of the enriched mixtures supplied at full-load. This effect is absent with vaporized LPG, yielding reduced engine intake air flow. Figure 7. The variation of volumetric efficiency for both fuels 7

Figure 8 illustrates the effect of two different valve lift (7 and 8 mm) on the engine brake power between 1700-3200 rpm engine speeds for unleaded gasoline and LPG fuels. As explained above, increasing of the valve lift in the experiments conducted with the gasoline fuel resulted in a reduction on the engine brake power at especially low engine speeds. Engine brake power decreased up to 5.66 % at 1700 rpm engine speed for 8 mm valve lift. This is due to a portion of air-fuel mixture during the part of the compression stroke forced back through the piston movement towards the TDC when the valve lift increased at the lower engine speeds. On the other hand, kinetic velocity of the mixture increases with increase of the engine speed. As it is seen from the figure 8, engine brake power shows increments at the higher engine speeds. Therefore, improvements on the engine performance characteristics with increasing trend were observed by the increase of valve lift at the higher engine speeds. Maximum engine brake power was obtained with gasoline fuel as 6.015 kW at 3200 rpm engine speed for 8 mm valve lift. Although the heating value of the LPG fuel is higher than the gasoline fuel, deteriorations on the engine performance were generally observed with LPG fuel for 7 mm valve lift in comparison with the gasoline fuel. In the results, it was found that the engine brake power reduced by 13.09 % at 3200 rpm with 7 mm valve lift when compared with gasoline fuel. This is caused from a reduction in the volumetric efficiency due to gas phase induction of the LPG fuel. However, the amount of LPG fuel taken into the cylinder increased by the increasing of the valve lifts and improvements on the engine brake power were achieved. As a result, an increase up to 7.17 % on the engine brake power with LPG fuel was obtained at 3200 rpm by increasing the valve lift to 8 mm.

Figure 8. The variations of brake power versus engine speed for standard and 8 mm valve lifts

Figure 9 shows the effect of two different valve lift (7 and 8 mm) on BSFC between 1700-3200 rpm engine speeds for unleaded gasoline and LPG fuels. As seen in the results, BSFC values were observed higher at all the engine speeds for LPG fuel when compared with gasoline fuel. Minimum BSFC was obtained at 2600 rpm engine speed with each experimental condition. The BSFC was obtained as 306.156 g/kWh at 2600 rpm engine speed for 8 mm valve lift and gasoline fuel. In the engine tests with LPG fuel, BSFC increased by 7.27 % at 2600 rpm engine speed for 7 mm valve lift when compared with gasoline fuel and it was found as 329.75 g/kWh. However, improvements on BSFC with LPG fuel were also achieved by increasing the valve lift to 8 mm. BSFC with LPG fuel was decreased by 5.35 % at 3200 rpm engine speed with the increase of valve lift. 8

Figure 9. Variations of BSFC versus engine speed with LPG and gasoline for standard and 8 mm valve lifts In Figure 10, the variations of thermal efficiencies between 1700-3200 rpm engine speeds are shown for two different valve lift (7 and 8 mm) with unleaded gasoline and LPG fuels. Thermal efficiency decreased with LPG fuel compared to gasoline fuel for two different valve lift. Density of LPG is lower compared to gasoline fuel. Therefore, more fuel should be supplied in order to obtain the same power output due to difference in the energy densities and the volumetric efficiencies of the LPG and gasoline fuels. Thus, BSFC values slightly increase and thermal efficiency decreases with LPG fuel as seen in Figure 9 and 10 respectively. Moreover, improvements on the thermal efficiency especially at the higher engine speeds were obtained due to improvements on the volumetric efficiency when the valve lift increased to 8 mm. Because, more inlet charge is inducted through the intake line with higher valve lift resulting in higher volumetric efficiency. Thus, thermal efficiency is also improved with 8 mm valve lift. In addition, it can be stated that heat transfer losses decrease at higher engine speeds. The homogeneity of the charge mixture improves at higher engine speeds allowing to obtain higher thermal efficiency especially with 8 mm valve lift. Maximum thermal efficiency for gasoline fuel was found to be 26.72 % at 2600 rpm engine speed and 8 mm valve lift while it was observed as 25.21 % for LPG fuel.

Figure 10. The effects of test fuels on thermal efficiency for standard and 8 mm valve lifts

Figure 11 shows the effect of two different valve lift (7 and 8 mm) on the exhaust gas temperature between 1700-3200 rpm engine speeds for unleaded gasoline and LPG fuels. As seen from the figure 11, exhaust gas temperature increased with the engine speed. Also, exhaust gas temperatures with LPG fuel were found to be higher at all the engine speeds compared to gasoline fuel. Moreover, depending on the amount of mixture taken into the cylinder, slightly increments on the exhaust gas temperatures were observed when the valve lift increased to 8 mm. Maximum exhaust gas temperature with LPG fuel was measured as 765 ºC at 3200 rpm engine speed for 8 mm valve lift.

Figure 11.The effects of two different valve lifts with LPG and gasoline on exhaust gas temperature versus engine speed

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Figure 12 shows the effect of two different valve lift (7 and 8 mm) on HC emissions between 1700-3200 rpm engine speeds for unleaded gasoline and LPG fuels. As can be seen from the results, HC emissions decreased with the increase of the engine speed. In-cylinder turbulence intensity and burn rate were enhanced with the increase of the engine speed. Therefore, HC emissions resulted from flame quenching decreased in crevice regions at the cylinder walls. Consequently, HC emissions for both fuels were generally improved with increase of the engine speed.

Figure 12.The variations of HC emissions versus engine speed with LPG and gasoline for different valve lifts

Minimum HC emissions with LPG fuel were measured as 65 ppm at 3200 rpm engine speed for 8 mm valve lift. HC emissions at the same engine speed were found higher by 61.54 % when the engine fueled with gasoline fuel and 7 mm valve lift and it was measured as 105 ppm. As seen from the results, HC emissions for both fuels were improved especially at the medium and high engine speeds with the increase of valve lift.

It can be emphasized that valve overlap period can be changed in order to reduce emissions. Emissions with LPG are higher according to gasoline at lower engine speeds. This situation results from higher inertia of gasoline liquid droplets. In addition, there is lower tendency of gasoline in order to follow intake air in its bypass line. HC emissions with LPG improve at higher engine speeds, because gas motion is controlled by ram and tuning effects in the intake line [15]. Moreover, more homogeneous charge mixture is obtained with the increase of LPG. So, better combustion occurs and lower HC is produced [2,3]. HC and CO are highly dependent on the cylinder gas temperature at the end of combustion. It can be said that higher gas cylinder temperature will enhance CO and HC oxidation. Thus, it causes to obtain lower HC and CO emissions [2,3,9]. It can be also stated that lower exhaust temperature allows for less oxidation of the hydrocarbons released from the crevices during expansion stroke. The temperature on cylinder wall is lower owing to coolant effect. This phenomena prevents to oxidize hydrocarbon molecules and causes to obtain lower exhaust gas temperature. Consequently, NO x emissions tend to decrease at lower exhaust gas temperatures [38-41].

Figure 13 and 14 show the effect of two different valve lift (7 and 8 mm) on CO and CO2 emissions between 1700-3200 rpm engine speeds for unleaded gasoline and LPG fuels 10

respectively. CO emissions are strongly affected with relative air-fuel ratio (λ) and also As it is seen from the results, lower CO emissions were obtained with the increase of the engine speed. Higher CO emissions may be expected at the higher engine speeds because the engine power shows increments due to providing more mixture or more rich fuel. However, combustion speed increases at the higher engine speeds and stoichiometric air/fuel rate were supplied for both of fuels [40]. Thus, low CO emissions were obtained with the increase of the engine speed. In addition, due to the its relatively lower C/H ratio and more homogeneous mixture supplied by a vaporizer to the upstream of inlet air in the throttle body of carburetor, lower CO emissions were obtained at λ=1 with LPG fuel for both valve lifts according to gasoline fuel [9, 15]. CO emissions at the 3200 engine speed and 7 mm valve lift were measured as 0.82 % for gasoline fuel while 29.27 % decrease was obtained with LPG and it was found as 0.58 %. Regarding to CO2 emissions, due to LPG fuel has lower carbon content than gasoline or diesel and it produces less CO2 which plays a major role in global warming during combustion. Lower CO 2 emission was measured with LPG according to gasoline as seen in Figure 14.

Figure 13. The effects of valve lifts on CO emissions with LPG and gasoline

Figure 14. The effects of valve lifts on CO2 emissions with LPG and gasoline

Figure 15 shows the effect of two different valve lift (7 and 8 mm) on NO x emissions between 1700-3200 rpm engine speeds for unleaded gasoline and LPG fuels. It is seen that the higher NOx emissions generally observed with an increasing the engine speed. Especially at the higher engine speeds (2900 and 3200 rpm), combustion temperatures increased depending on the increments of the fuel mass taken into the cylinder and this results in higher NOx emissions. Moreover, heating value and burning speed of the LPG fuel are higher than the gasoline fuel with lack of charge cooling effect which obtained with gasoline fuel by its evaporation and also air-fuel mixture taken into the cylinder increased with the increase of the valve lift [41-43]. As a result of these, NOx emissions in the LPG fueled engine tests showed 6.4 % increase at 3200 rpm engine speed when the valve lift increased to 8 mm. Also, NOx emissions were found to be higher by 10.30 % at 3200 rpm engine speed and 8 mm valve lift when the compared with gasoline fuel.

Figure 15. The effects of valve lifts and test fuels on NOx emissions

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5. CONCLUSIONS In this study, a single-cylinder, four-stroke, single overhead camshaft (SOHC), spark ignition (SI) gasoline engine was converted to run with liquefied petroleum gas (LPG) fuel. The camshaft of the engine was re-designed using classical spline method for different valve lifts. The variations of engine brake torque, power, BSFC, HC, CO and NOx emissions and exhaust gas temperature were investigated with unleaded gasoline and LPG fuels for two different valve lifts (7 and 8 mm). It is observed that engine torque and power decreased and BSFC increased when the engine was converted to LPG fueling and 7 mm valve lift. In addition, improvements on the HC and CO emissions were observed with LPG fuel while NOx emissions increased. Also, improvements on the engine performance results depending on increasing the amount of mixture taken into the cylinder were found with LPG fuel when the valve lift increased to 8 mm at higher than 2000 rpm engine speeds.

ACKNOWLEDGMENTS This study was supported by the Gazi University Scientific Research Foundation in frame of the project code of TEF 07/2011-08. Authors would like to thank the supports of Gazi University.

NOMENCLATURE

BSFC

Brake specific fuel consumption

CAD

Computer aided design

CNG

Compressed natural gas

CO

Carbon monoxide

CO2

Carbon dioxide

HC

Hydrocarbon

HCCI

Homogeneous charged compression ignition

ICE

Internal combustion engine

LPG

Liqufied petroleum gas

NOx

Nitrogen oxides

SFC

Specific fuel consumption

SI

Spark ignition

SOHC

Single overhead camshaft 12

Std

Standard

TDC

Top dead center

WOT

Wide open throttle

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P. Sıkıştırma Oranı Artışının LPG ile Çalışan Buji ile

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33. Demirci O.K., Buji ile ateşlemeli bir motorda Miller çevrimi uygulaması performans ve emisyon karakteristiklerinin incelenmesi, Yüksek Lisans Tezi, GÜFBE, Ankara, 2013. 34. Norton R.L. Cam Design and Manufacturing Handbook, 67, Industrial Press Inc., 10016-4078, United States of America, 2002. 35. Karabulut H, Sarıdemir S. Farklı Supap Açık Kalma Süreleri ve Kursları İçin Klasik Spline Yöntemi İle Elde Edilen Kam Profillerinin Karşılaştırılması. Journal of the Faculty of Engineering and Architecture of Gazi University, 2009; 24: 509-515. 36. Tsay D.M., Huey C.O. Spline Functions Applied to the Synthesis and Analysis of Nonrigid Cam-Follower Systems. Journal of Mechanisms Transmissions and Automation in Design 1989; 111:561-569. 37. TMMOB, Araçlarda LPG Dönüşümü, 13-17, Ankara, 1999. 38. TÜPRAŞ A.Ş., Yakıt Özellikleri Test Sonuç Tablosu, İzmit, 1996. 39. Çınar, C., Uyumaz, A., Homojen Dolgulu Sıkıştırma İle Ateşlemeli Bir Benzin Motoru İçin Kam Tasarımı Ve İmalatı, Journal of the Faculty of Engineering and Architecture of Gazi University, 2014, 29, 1, 15-22. 40. Borat, O., Sürmen, A., Balcı, M., İçten Yanmalı Motorlar, Gazi Üniversitesi Teknik Eğitim Fakültesi vakfı yayınları, Ankara,1992. 41. Borat, O., Balcı M., ve Sürmen, A., Hava kirlenmesi ve Kontrol Tekniği, Teknik Eğitim Vakfı Yayınları-3, Ankara, 25,1994. 42. Ergeneman, M., Kutlar, A., Mutlu, M., Arslan, H., Taşıt Egzozundan Kaynaklanan Kirleticiler, Birsen Yayınevi, İstanbul, Türkiye,1998. 43. Murillo, S., Mı´guez, J.L., Porteiro, J., Viability of LPG use in low-power outboard engines for reduction in consumption and pollutant emissions, Int. J. Energ. Res. 2003, 27,467-480.

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FIGURE LIST Figure 1. The overall layout of the experimental set up Figure 2. Images of manufactured cam profiles Figure 3. Displacement curves of the cam profiles Figure 4. Velocity curves of cam profiles Figure 5. Acceleration curves of cam profiles Figure 6. The variations of engine brake torque versus engine speed with LPG and gasoline Figure 7. The variation of volumetric efficiency for both fuels Figure 8. The variations of brake power versus engine speed for standard and 8 mm valve lifts Figure 9. Variations of BSFC versus engine speed with LPG and gasoline for standard and 8 mm valve lifts Figure 10. The effects of test fuels on thermal efficiency for standard and 8 mm valve lifts Figure 11.The effects of two different valve lifts with LPG and gasoline on exhaust gas temperature versus engine speed Figure 12.The variations of HC emissions versus engine speed with LPG and gasoline for different valve lifts Figure 13. The effects of valve lifts on CO emissions with LPG and gasoline Figure 14. The effects of valve lifts on CO2 emissions with LPG and gasoline Figure 15. The effects of valve lifts and test fuels on NOx emissions

Figure 1. The overall layout of the experimental set up

Figure 2. Images of manufactured cam profiles

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Figure 3. Displacement curves of the cam profiles

Figure 4. Velocity curves of cam profiles

Figure 5. Acceleration curves of cam profiles

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Figure 6. The variations of engine brake torque versus engine speed with LPG and gasoline

Figure 7. The variation of volumetric efficiency for both fuels

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Figure 8. The variations of brake power versus engine speed for standard and 8 mm valve lifts

Figure 9. Variations of BSFC versus engine speed with LPG and gasoline for standard and 8 mm valve lifts

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Figure 10. The effects of test fuels on thermal efficiency for standard and 8 mm valve lifts

Figure 11.The effects of two different valve lifts with LPG and gasoline on exhaust gas temperature versus engine speed

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Figure 12.The variations of HC emissions versus engine speed with LPG and gasoline for different valve lifts

Figure 13. The effects of valve lifts on CO emissions with LPG and gasoline

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Figure 14. The effects of valve lifts on CO2 emissions with LPG and gasoline

Figure 15. The effects of valve lifts and test fuels on NOx emissions

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TABLE LIST Table 1. The specifications of the test engine Table 2. The technical specifications of the exhaust gas analyzer Table 3. The chemical properties of the test fuels

Table 1. The specifications of the test engine Engine model Cylinder number Swept volume [cm3] Bore & Stroke [mm] Compression ratio Maximum engine speed [rpm] Valve system Fuel Valve lift [mm] Cooling system Maximum brake power [kW at 3800 rpm] Maximum brake torque [Nm at 2600 rpm]

Four stroke, spark ignition 1 338 82 x 64 8.5:1 3800 OHC Dual fuel (Gasoline and LPG) 7 (Std valve lift ) 8 (high valve lift) Air cooled 8.1 23.7

Table 2. The technical specifications of the exhaust gas analyzer CO [%] CO2 [%] HC [ppm] NOx [ppm] O2 [%] Lambda

Operating range 0 – 15 0 – 20 0 – 9999 0 – 5000 0 – 25 0.6 – 1.2

Accuracy 0.001 0.1 1 1 0.01 0.001

Table 3. The chemical properties of the test fuels [37,38] Chemical formula Density [g/cm3 at 15.56 ºC] Octane number Vaporization temperature [°C] Calorific value [kJ/kg] Stoichiometric air/fuel ratio

Unleaded gasoline C6.9 H14.6 0.7697 95 20-200 43932 14.7

LPG C3.7 H9.4 0.53 105 -42 46100 15.5

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HIGHLIGHTS 

Volumetric efficiency improved with the increase of valve lift in case of LPG usage.



Lower CO and HC emissions were obtained with LPG compared to gasoline.



NOx emissions increased with LPG according to gasoline for both valve lifts due to higher cylinder gas temperature.



Engine performance values with LPG get closer to the gasoline when higher valve lift is used.

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