Copyright © 2009 KSAE 1229−9138/2009/045−01 International Journal of Automotive Technology, Vol 10, No 2, pp 131−139 (2009) DOI 10.1007/s12239−009−0016−2 COMBUSTION AND EMISSION CHARACTERISTICS OF BD20 REFORMED BY ULTRASONIC ENERGY FOR DIFFERENT INJECTION DELAY AND EGR RATE IN A DIESEL ENGINE 1) 2) S Y IM , D S CHOI 3)* and J I RYU Graduate School of Mechanical Engineering, BK21 Mechatronics Group, Chungnam National University, Daejeon 305-764, Korea Division of Mechanical & Automotive Engineering, Kongju National University, Chungnam 330-717, Korea Department of Mechanical Engineering, BK21 Mechatronics Group, Chungnam National University, Daejeon 305-764, Korea 1) 2) 3) (Received 25 April 2007; Revised 11 September 2008) ABSTRACT−The purpose of this study is to understand the operational characteristics of a diesel engine that uses BD20 reformed by ultrasonic energy irradiation In particular we study the effects of tuning injection delay and EGR rate BD containing about 10% oxygen has attracted attention due to soaring crude oil prices and environmental pollution This oxygen decreases soot by promoting combustion, but it also increases NOx To solve this problem, injection timing may be delayed or an EGR system may be applied These adjustments normally lower engine power and increase exhaust emission but, in using fuel reformed by ultrasonic energy irradiation (which is changed physically and chemically to promote combustion), we may hope to circumvent this problem To control the duration of the ultrasonic energy irradiation, the capacity of the chamber in an ultrasonic energy fuel supply system was tested at 550cc and 1100cc capacities As for the results of the experiment, we could identify the optimum EGR rate by investigating the engine performance and the characteristics of exhaust emissions according to the injection timing and the EGR rate while ultrasonically irradiated BD20 was fed to a commercial diesel engine With UBD20 (at an injection timing of BTDC 16o), the optimum EGR rate, giving satisfactory engine performance and exhaust emissions characteristics, was in the range of 15~20% KEY WORDS : BD (biodiesel fuel), BD20 (diesel 80% + biodiesel fuel 20%), EGR (exhaust gas recirculation), Injection delay, UBD (ultrasonic energy irradiated biodiesel fuel), Ultrasonic energy irradiation compounds other than NOx are known increase with an increase of the EGR rate There are also a few problems to solve in order for it to be put into practice universally, including contamination of the engine induction system by increase of the break specific fuel consumption (BSFC) and soot, the abrasion and corrosion of parts in the engine, and the blazing fire of lubricating oil (Lue et al., 2001; Ham and Chun, 2002) When fuel is irradiated by ultrasonic energy, the fuel undergoes physical and chemical changes induced by the energy of the ultrasonic irradiation For example, the aromatic constituents become constituents of the fatty group, and the isoparaffins turn into normal paraffins This leads to an increase in the cetane number and heating value, while decreasing viscosity, surface tension, and the spray diameter (SMD) In this way, fuel quality is reformed, physically and chemically, promoting combustion and decreasing soot (Choi, 1996; Jeong et al., 1991; Lee and Ryu, 2003; Song, 2005) There is a trade-off however, as NOx reduction leads to the increase of soot, while soot reduction leads to the INTRODUCTION Due to soaring crude oil prices and environmental problems, interest in biodiesel fuel (hereafter called BD) has grown BD is similar to diesel fuel and can be applied to commercial diesel engines without any special modification Although BD contains about 10% oxygen and thereby decreases soot by promoting combustion, this active combustion leads to an increase in NOx emissions due to the increase in combustion temperature (Agarwal et al., 2006; Ryu and Oh, 2003; Baik, 2006; Bae et al., 2002; Oh et al., 2002) In particular, BD20, which is a blend of diesel fuel and BD in a volume ratio of 8:2, contains a substantial quantity of O , making it particularly effective in reducing soot (Baik, 2006; Bae et al., 2002; Ryu and Oh, 2003) To overcome this problem, the EGR (Exhaust Gas Recirculation) system has been widely put into practical use The EGR system is inexpensive to install, but emission of *Corresponding author e-mail: ryuji@cnu.ac.kr 131 132 S Y IM, D S CHOI and J I RYU increase of NOx Hence, it is very difficult to reduce both quantities simultaneously The fuel injection timing is markedly delayed to reduce NOx, because this leads to a raise in the temperature of combustion The temperature at the intake also increases when using hot EGR Alternatively, cooled EGR may be used to display a constant effect in the range over mid-load The EGR method has been widely applied to small diesel vehicles but the soot in the exhaust gas contains sulfur oxides that enter the engine, causing enhanced wear on the piston and cylinders The life of the engine oil is also badly affected Hence it is essential to designate the driving range with a large amount of NOx in order to maintain an appropriate EGR rate (Uchida, 1993) Therefore, this study aims to decide the optimum injection timing and the EGR rate to obtain a simultaneous reduction of soot and NOx to within minimum values, without deteriorating engine performance using BD20 reformed by ultrasonic energy irradiation EXPERIMENTAL SYSTEM AND METHODS 2.1 Ultrasonic Energy Fuel Supply System Figure provides a schematic diagram for the ultrasonic energy fuel supply system used for ultrasonic irradiation The specifications of the transducer used in this experiment are presented in Table A bolted Langevin transducer (BLT) was used for the ultrasonic energy fuel supply system Its structure is such that when an ultrasonic oscillator (50W) functions at AC 220V, ultrasonic vibrations are produced at 28 kHz and are transmitted through the horn and into the fuel To maximize the ultrasonic energy irradiation, fuel is supplied to the lower part of the chamber of the ultrasonic energy fuel supply system and flows out through the upper part An air vent was installed in the back of the upper reflector of the chamber so that the air bubbles generated by the ultrasonic cavitations could escape (Dale Ensminger, 1988) The ultrasonic energy fuel supply system was connected between a fuel flowmeter and an injection pump so that the reformed (irradiated) fuel could be provided to the engine 2.2 Experimental System and Method The schematic diagram and photograph of the experimental apparatus is presented in Figures and Figure The apparatus consists of a dynamometer, a test engine, measurement instruments, and a data acquisition system The specifications of the test engine are shown in Table This experiment was performed according to the KSRISO Figure Schematic diagram of experimental apparatus Figure Schematic diagram of an ultrasonic energy fuel supply system Table Specifications of the bolted Langevin Transducer (BLT) Items Specifications Frequency (kHz) 28±0.4 Admittance (mΩ) 35±7 Thermal quality (Qm) 1,000 Capacitance (pF) 3000±15% Maximum velocity (cm/s) 60 Maximum altitude (µm) 9.6 Dia & Thickness (mm) φ 29.5 & Figure Photograph of experimental apparatus COMBUSTION AND EMISSION CHARACTERISTICS OF BD20 REFORMED BY ULTRASONIC ENERGY Table Specifications of test engine Items Specifications Engine type Water cooled stroke cycle cylinder diesel engine Combustion chamber type Swirl combustion chamber Valve mechanism O.H.C (Over Head Cam shaft) Injection pump Distributor type Bore×Stroke 91.1×95 mm Total displacement 2,476cc Max power 77ps/4,200 rpm Max torque 15.5 kgf·m/2,000 rpm Fuel ignition timing BTDC 16o Coolant temperature 80±2 oC Ignition order 1-3-4-2 Table Properties of test fuels Biodiesel Fuel Items BD20 BD100 o 48 174 Flash point (PM, C) Pour point (oC) −17.5 −2.5 Sulfer (Wt %) 0.018 0.011 Specific gravity (15/4oC) 0.8317 0.8815 Cetane number 50.5 57.5 Kinematic viscosity 2.614 4.255 (40oC, cSt) Oxygen content (%) − 11.03 Diesel Fuel 44 −17.5 0.022 0.8211 51.8 2.350 2534 testing standard (KSRISO, 2003) The engine load is adjusted after fixing the engine speed Also, the injection timing was set for BTDC 11o and 16o, with the engine load set to 25%, 50%, 75% and 100% according to a maximum torque for each engine speed The engine speed was varied from 1000 rpm to 3500 rpm in 500 rpm intervals Table shows properties of the test fuels used for the experiment BD is made out of soybean oil and in our tests was blended with 20% (by volumetric ratio) commercial diesel fuel In order to investigate the effects of the duration of the ultrasonic energy irradiation, the capacity of the chamber for the ultrasonic energy fuel supply system was set to either 500cc or 1100cc If the capacity of the chamber is too small, the influence of the ultrasonic energy irradiation is not significant, and if the capacity of the chamber is too large, the temperature of the supplied fuel becomes high enough to negatively affect the engine The amount of recirculating exhaust gas is controlled by the EGR valve after measuring the intake air volume (m3/h) The EGR rate was computed using the following formula (1): V – V-a × 100 EGR rate ( % ) -(1) V0 133 Table Specifications of measuring equipment Items Specifications Co Model HE-130 Dynamometer Hwanwoong Absorption torque: 35 kgf·m Pressure Kistler Co type 6052B transducer Piezoelectric pressure transducer Charge Kistler Co type 5011B amplifier Oscilloscope Tectronic Co type DS360 A/D-D/A National Ins Co type converter PCI-6024E Load cell Jungwoo Co type JW-U2SB AND Co type HF-2000GD Fuel flow meter Capacity: 2100g, Resolution: 0.01g Kwang precision Co type Gold 707 Smoke meter Su Measurable range: 0~100%±2% F.S HORIBA KOREA Ltd MEXA Chemical method NOx analyzer 554JKNOX Measurable range: 0~5,000 ppm ±20 ppm BOSCH ETT 008.55 Non-Dispersive Infrared Method CO analyzer Measurable range : 0.00~10.00% vol ±0.06% vol Here, V0 is intake air volume (m3/h) with no EGR, while Va is that when EGR is taken into account Since the temperature of the EGR gas changes in accordance with each engine load, it was controlled here to be 24oC by using a cooling circulation system A filter was used to remove particles in the recirculated exhaust gas The temperature of the cooling water was maintained at a constant 80±2oC, regardless of the testing condition After the completion of each experiment, the fuel filter was replaced, and the fuel supply system was examined for need of repair to ensure that previous experiments would not affect subsequent ones The list of equipment used for testing engine performance, combustion characteristics, and exhaust emissions is presented in Table CHARACTERISTICS OF INJECTION DELAY Figure shows the relationship between the engine power and the engine speed for the test fuels (commercial diesel, BD20) according to the amount of ultrasonic energy irradiation Here, the chamber capacities were 550cc and 1100cc at fuel injection timings of BTDC 11o and BTDC 16o For the BTDC 16o case, the engine power of commercial diesel fuel was 0~3% higher than that for BD20 With regard to total engine speed, UBD20 was 0~2% higher than 134 S Y IM, D S CHOI and J I RYU diesel with a chamber capacity of 550cc, and 1~6% higher than diesel with a chamber capacity of 1100cc In other words, the engine power was enhanced the most when using irradiated fuel For the BTDC 11o case, when the fuel injection timing was delayed and ultrasonic irradiation was applied, the engine power was enhanced or remained almost the same within a 2~3% margin as compared to BD20 over the entire range of speeds The fuel injection timing was delayed to ensure optimum fuel injection timing for NOx reduction Although this delay has the effect of reducing engine power, the fuel reformation effect due to ultrasonic irradiation caused a compensating increase in power Hence, the overall engine power observed for UBD20 was similar to that for BD20 In fact, the engine power characteristics observed for BD20, UBD20 and diesel were similar throughout the whole range of engine speeds used here With a fuel injection timing of BTDC 16o, the 1100cc chamber configuration showed a particular tendency toward power increase This implies that the heating value of BD is lower than that of diesel, but that fuel reformation, achieved by ultrasonic energy irradiation lead to increased thermal efficiency Figure shows the maximum combustion pressure for cases with and without ultrasonic irradiation with fuel injection timings of BTDC 16o and BTDC 11o At BTDC 16o, the maximum combustion pressure of UBD20 increased by 5% using the 550cc chamber, and by approximately 2~6% with an 1100cc chamber In addition, the UBD20 maximum combustion pressure was found to be larger in the 550cc case by approximately 2~3% over that for the 1100cc at BTDC 11o (the injection timing was delayed compared to that used for BD20) This is because the fuel reformed by the ultrasonic irradiation promotes combustion via an improvement in ignition This is indicative of promoted evaporation of fuel and reduced Sauter mean diameter (SMD) of droplets as compared to the case of BD20 As stated above, the optimum fuel injection timing for Figure Comparison of engine power under varying engine speed at engine load 75% Figure Comparison of Pmax under varying load at engine speed of 2,000 rpm reduction of NOx in UBD20 is more delayed than that for BD20, and thus the maximum combustion pressure is lower However, as presented in Figure 5, increased duration of irradiation leads to somewhat of an increase in the maximum combustion pressure Accordingly, to ensure optimum fuel injection timing for UBD20, the maximum combustion pressure was reduced slightly by delaying the fuel injection timing However, providing enough duration of ultrasonic energy irradiation contributed to an effective fuel reformation, which improved combustion The improvement seems to be due to the fact that the maximum combustion pressure was similar to that for BD20 at BTDC 16o Figure compares the combustion pressure, the heat release rate and the mass burning rate of UBD20 with 1100cc chamber and BTDC 11o timing, diesel and BD20 at the standard optimum timing, BTDC 16o The engine load was held at 75%, and the engine speed at 2,000 rpm When UBD20 was supplied to the engine, its combustion started slightly later than that for BD20, although it was found to have similar characteristics essentially, when ultrasonic energy irradiation was performed on BD20 (used at BTDC 11o), its ignition delay and the combustion duration were shortened due to acceleration of combustion It is thought because the 10% oxygen content of BD actively promotes combustion It is also thought that the ultrasonic energy reforms fuel quality physically and chemically leading to an increase in heating value and ignition quality, while decreasing the viscosity, the surface tension and the spray diameter (SMD) size Figure shows the brake specific fuel consumption (BSFC) of the engine according to the duration of ultrasonic energy irradiation (as implied by the chamber capacity) at fuel injection timings of BTDC 11o and BTDC 16o At BTDC 16o, the BSFC of commercial diesel fuel was 1~2% higher than that of BD20 Over the whole range of engine speed, the BSFC of UBD20 was 1~2% lower with a 550cc chamber, and 1~3% lower with a 1100cc chamber Thus, the BSFC was most enhanced for the irradiated COMBUSTION AND EMISSION CHARACTERISTICS OF BD20 REFORMED BY ULTRASONIC ENERGY 135 Figure Comparison of BSFC under varying engine speeds at an engine load of 75% Figure Comparison of NOx under varying engine speeds at an engine load of 75% Figure Comparison of cylinder pressure, heat release rate and mass burning rate at an engine speed of 2,000 rpm and load of 75% fuel With delayed timing, UBD20 showed a BSFC that was better than the commercial diesel by 1~2% over the whole range of engine speeds As mentioned above, it was anticipated that BSFC would be deteriorated by delaying the fuel injection timing in order to obtain optimal NOx reduction for UBD20 In reality, for fuel reformed by sufficient ultrasonic energy irradiation, the overall BSFC was enhanced Furthermore, BSFC gradually decreased with the amount of irradiation of BD, but not when such a procedure was applied to commercial diesel It is believed that the oxygen contained in BD promotes combustion, which then leads to enhanced combustion efficiency Figure shows NOx characteristics according to engine speed and the duration of ultrasonic energy irradiation given to the test fuels (commercial diesel, BD20, where duration is implied by chamber capacity) Figure Comparison of soot concentration under varying engine speeds at an engine load of 75% The engine load was 75% and the fuel injection timing was set to BTDC 11o or BTDC 16o At BTDC 16o, NOx emission from commercial diesel fuel was 3~5% less than that of BD20 over the whole range of engine speeds UBD20 NOx was 4~26% higher than BD20 with a 550cc chamber, and 25~42% higher with an 1100cc chamber 136 S Y IM, D S CHOI and J I RYU As mentioned in the discussion of engine performance, the ultrasonic energy irradiation reformed the fuel quality physically and chemically, which promoted combustion This leads to a pressure increase in the combustion chamber, and a resultant increase in combustion temperature Higher temperature leads to increased NOx emissions as compared to BD20 NOx tends to generally increase with BD content, because oxygen contained in BD promotes combustion, thereby raising the combustion chamber temperature When the fuel was irradiated, NOx was remarkably increased as a result of the reformed fuel Figure shows the soot characteristics according to engine speed depending on the duration of irradiation (implied by chamber capacity) The engine load was 75% with fuel injection timings of BTDC 11o and BTDC 16o The soot of commercial diesel fuel was 13~60% higher than that from BD20 over the entire speed range For UBD20, it was 13~33% lower with a 550cc chamber and 40~67% lower an 1100cc chamber Notably, when the fuel injection timing was delayed to BTDC 11o, together with the ultrasonic energy irradiation, the soot level was 20~ 60% lower than that for BD20 over the entire speed range Although the combustion duration was not enough (due to the delayed timing), the soot was reduced because of the physical and chemical properties of irradiated fuel Figure 11 Comparison of engine power under varying EGR Rates at engine load of 75% (2000 rpm) Figure 10 shows the maximum combustion pressure according to the EGR rate and irradiation at timings of BTDC 16o and BTDC11o for each of the test fuels (commercial diesel fuel and BD20) For UBD20 at BTDC 16o, the decrease of the maximum pressure with the EGR rate showed a minimum of 1.4% at an EGR of 20%, while showing a dramatic decrease of 5% at an EGR rate of over 30% It is thought that, at an EGR rate of over 30%, the maximum combustion pressure quickly decreases because the concentration of oxygen becomes insufficient for combustion Figure 11 shows the relationship between the engine power and the EGR rate for the test fuels (commercial diesel, BD20) according to irradiation when the engine speed is 2000 rpm and engine load is 75% with fuel injection timings of BTDC 11o and BTDC 16o For BTDC 16o, the engine power of commercial diesel fuel was 4~11% higher than that for BD20 For UBD20, the engine power was 6~11% higher with an 1100cc chamber, and 4~5% higher with a 550cc chamber For BTDC 11o, the engine power was increased by 6~8% When the EGR was applied, the engine power of BD20 tended to decrease more than that of the commercial diesel fuel With increased irradiation, the engine power increased, similar to the non-EGR case Figure 12 shows the relationship between the BSFC and the EGR rate of test fuels (commercial diesel, BD20) according to irradiation with an engine speed of 2000 rpm and engine load of 75% and timings of BTDC 11o and BTDC 16o At BTDC 16o, depending on the EGR rate, the BSFC of commercial diesel fuel was larger by 2~4% than that of BD20 The BSFC for UBD20 was about 3~5% lower than Figure 10 Comparison of Pmax under varying EGR Rate at engine speed of 2,000 rpm Figure 12 Comparison of BSFC under varying the EGR Rates at engine load of 75% (2000 rpm) CHARACTERISTICS RELATED TO CHANGES OF EGR RATE COMBUSTION AND EMISSION CHARACTERISTICS OF BD20 REFORMED BY ULTRASONIC ENERGY Figure 13 Comparison of NOx under varying the EGR Rates at engine load 75% (2000 rpm) that for BD10 while using an 1100cc chamber, and about 2% lower while using a 550cc chamber At BTDC 11~ the BSFC for UBD20 was about 3% lower Varying the fuel injection timing at an EGR rate of 10% does not make a significant difference in the BSFC under identical engine speed and load However, the range of fluctuation tended to expand with increasing EGR rate Figure 13 shows the relationship of NOx according to the EGR rate and irradiation for the test fuels (commercial diesel, BD20) at an engine speed of 2000 rpm and load of 75% with timings of BTDC 11o and BTDC 16o When the fuel injection timing was set to BTDC16o, the NOx from commercial diesel fuel was 2~8% lower than that of BD20 UBD20 NOx was 5~8% higher than BD20 with a 550cc chamber, and 8~20% higher with an 1100cc chamber At BTDC 11o, NOx was decreased by 5~8% compared to BD20 over the whole range of engine speed Against this backdrop, it was reassuring that reduction of NOx was greatly affected by the fuel injection timing NOx was dramatically decreased in accordance with the increase of the EGR rate, especially in the 40% range where the reduction was most notable When EGR was applied to the engine, some of the air inhaled into the combustion cylinder was replaced with inert exhaust gas Because of this combustion temperature was lowered and combustion was delayed, eventually leading to a remarkable reduction of NOx NOx emissions were, therefore, rapidly reduced with an increase of the EGR rate In addition, the NOx reduction rate was found to increase with increasing engine load, but it could be predicted that exhaust emissions would be remarkably increased due to the decrease of oxygen Figure 14 shows the relationship between soot and the EGR rate of the test fuels (commercial diesel, BD20) according to irradiation at an engine speed of 2000 rpm, and load of 75% with timings of BTDC 11o and BTDC 16o 137 Figure 14 Comparison of soot under varying EGR Rates at an engine load 75% (2000 rpm) When the fuel injection timing was delayed together with application of ultrasonic energy irradiation, soot was decreased by 34~43% over the entire range when compared to the soot from commercial diesel fuel Although the combustion duration was insufficient due to the delayed fuel injection timing, the soot was reduced because of various factors related to the ultrasonic energy that promote combustion In other words, soot increased with an increase in EGR rate, but the case of mixed diesel/BD emitted less soot than with diesel alone When the EGR rate was more than 20%, soot was increased over the whole range The recirculated exhaust gas reduced the amount of oxygen in the intake air that was inhaled into the combustion chamber, disturbing the combustion process In addition, when the EGR was applied to BD20, soot was reduced by a larger amount than was seen with diesel fuel alone This is because oxygen contained in BD promoted oxidation of the fuel It is thought that oxygen contained in the fuel promoted combustion by prompting chemical reactions with hydrocarbons Exceptional soot reduction was achieved over the whole range of the EGR rate due to the irradiation This is because the ultrasonic fuel reformation, together with biodiesel fuel elements, contributed to combustion promotion Figures 15 and 16 show the correlation of the BSFC, NOx, engine power and soot with cooled EGR rate at an engine speed of 2000 rpm and load of 75% for BD20 at BTDC 16o, and for ultrasonically reformed BD20 at BTDC 11o The BSFC and soot for both BD20 and the reformed fuel (UBD20) increased in accordance with the increase of the EGR rate, while engine power and NOx tended to gradually decrease Soot increased with the increase in the EGR rate, but it was emitted relatively less with BD20 than with commercial diesel fuel Soot was also emitted relatively less from the irradiated fuel, UBD20 However, with an EGR rate of more than 20%, the soot 138 S Y IM, D S CHOI and J I RYU considerations simultaneously is in the range of 10~20% For UBD20 at BTDC 16o and EGR rate larger than 20%, soot levels were similar or a little more than in the case of the commercial diesel fuel or BD20 If the EGR rate was less than 5%, NOx levels were similar to the case of commercial diesel fuel Therefore, when UBD20 was used at the fuel injection timing of BTDC 16o, the optimum EGR rate should be 15~20% to reduce both soot and NOx Against this backdrop, the optimum EGR rate should be considered in the range that does not deteriorate characteristics of the engine performance and minimizes exhaust emissions CONCLUSION Figure 15 Comparison of NOx vs BSFC under varying the EGR Rates at engine load of 75% (2000 rpm) Figure 16 Comparison of Power vs Soot under varying the EGR Rates at engine load of 75% (2000 rpm) rapidly increased This is because the recirculated exhaust gas reduces the amount of oxygen sucked into the combustion chamber, resulting in insufficient oxygen for combustion In addition, NOx was dramatically reduced in accordance with the increase in EGR rate As described previously, this feature of the EGR is due to lower combustion temperature and slackened combustion speed Therefore, for UBD20 at BTDC 16o, the optimum EGR rate to satisfy the BSFC, NOx, engine power and soot We studied the use of fuel reformed by ultrasonic energy irradiation in diesel engines in the context of optimizing performance and emissions In particular, we studied the tuning of fuel injection timing and EGR rate to obtain the following results: (1) The maximum combustion pressure of the chamber increased by up to 6% with an engine speed of 2,000 rpm and load of 75% upon irradiating BD20 When UBD20 was used with injection further delayed by 5o, the pressure increased by up to 3% (2) For the reduction of NOx from biodiesel fuel (an oxygenated fuel with high NO), the optimum injection timing of the fuel reformed by ultrasonic energy irradiation should be delayed compared to that of commonly used diesel fuel As regards BSFC, the results were found to improve as the ultrasonic energy irradiation duration became longer (the chamber capacity larger) (3) NOx emission from UBD20 was 42% higher than BD20 over the whole range of this experiment, while soot was a maximum of 67% lower (4) When BD20 was used with a fuel injection timing of BTDC 16o, the optimum EGR rate providing satisfactory BSFC and engine power was in the range of 10~20% (5) When BD20 was used with the fuel injection timing of BTDC 16o, the optimum EGR rate for reduction of soot and NOx was in the range of 15~20% When the fuel reformed by the ultrasonic energy irradiation was applied to the diesel engine, the optimum EGR rate was identified to be 15~20% to reduce NOx and to promote the BSFC Also, when the fuel injection timing was delayed and the duration of the ultrasonic energy irradiation was prolonged, the reduction effect increased For reformed fuel and delayed timing (UBD20 with BTDC 11o), engine power and BSFC were enhanced, while soot and NOx were both reduced as compared to BD20 levels We find that in order to enhance engine performance and reduce exhaust emissions it is essential to precisely control the injection timing and the duration of ultrasonic energy irradiation and to consider the optimum EGR rate COMBUSTION AND EMISSION CHARACTERISTICS OF BD20 REFORMED BY ULTRASONIC ENERGY REFERENCES 139 Engineers , , 65−71 KSRISO 2534 (2003) Load Vehicle - Engine Test Method Gross Shaft Power, Korean Agency for Technology and Standards Gyeonggi Korea Lee, B H and Ryu, J I (2003) A study on relationship between fuel characteristics and combustion characteristics of reformed diesel fuels by ultrasonic energy irradiation(II)-Relationship between chemical structure and cetane number- Trans Korean Society of Automotive Engineers , , 64−71 Lue, Y F., Yeh, Y Y and Wu, C H (2001) The emission characteristics of a small D I diesel engine using biodiesel blended fuels J Environmental Science and Health , , 845−859 Oh, Y T., Choi, S H and Kim, S W (2002) A study on characteristics of rise bran oil as an alternative fuel in a diesel engine(I), Trans Korean Society of Automotive Engineers , , 15−22 Ryu, K H and Oh, Y T (2003) A study on the usability of biodiesel fuel derived from rice 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the field test SAE Paper No 2003-08-0016 Taniguchi, M (2003) The present condition and promotion of idling stops on traffic SAE Paper No 2003-08-0014 International Journal of Automotive Technology, Vol 10, No 2, pp 251−264 (2009) DOI 10.1007/s12239−009−0030−4 Copyright © 2009 KSAE 1229−9138/2009/045−15 DEVELOPMENT OF A DRIVING CYCLE FOR THE MEASUREMENT OF FUEL CONSUMPTION AND EXHAUST EMISSIONS OF AUTOMOBILES IN BANGKOK DURING PEAK PERIODS S TAMSANYA, S CHUNGPAIBULPATANA and B LIMMEECHOKCHAI * School of Manufacturing Systems and Mechanical Engineering, Sirindhorn International Institute of Technology, Thammasat University, P.O Box 22 Thammasat Rangsit Post Office, Patumthani 12121, Thailand (Received 28 June 2007; Revised 23 September 2008) ABSTRACT−The exhaust emissions and fuel consumption rates of newly registered automobiles in Thailand are currently assessed using the standard driving cycle of the Economic Commission of Europe (ECE) Because of the highly different driving conditions, the assessment results may not reflect realistic amounts of emissions and fuel consumption for vehicles in Bangkok traffic, which is well known for its congestion The objective of this study is therefore to develop a new driving cycle for vehicles traveling on Bangkok’s main roads during peak traffic hours This paper first presents the development of a method for selecting representative road routes with traffic conditions that are representative of traffic in Bangkok for conducting real-world driving speed data collection These real-world data are obtained by driving a car equipped with a speed-time data logger along those selected road routes Several driving characteristics, including various profiles of microtrips, are analyzed from the collected speed-time data, and a number of target driving parameters are then defined for use as a set of criteria to justify the best driving cycle A procedure for generating driving cycles from the analyzed real-driving data is also developed, and the method to select the cycle that is most representative of Bangkok traffic is described Comparisons found in the study show that the target driving parameters of the newly developed driving cycle are much closer to those obtained from the real-world measured data than those calculated from the presently used European drive cycle This would imply that the obtained driving cycle will produce more realistic results of the emissions and fuel consumption assessment tests for vehicles traveling in Bangkok The methods developed in this study for route selection and driving cycle construction can easily be adopted by other big cities to develop their own vehicle driving cycles Furthermore, although the developed methods are for passenger cars, similar approaches can be applied to develop driving cycles for other types of vehicle, such as city buses and pick-up trucks KEYWORDS : Driving cycle, Driving pattern, Driving characteristics, Exhaust emissions, Fuel consumption It is well known that the emissions and fuel consumption rate of a vehicle are influenced by its design parameters, as well as the operating conditions (Andre et al., 1995; Booth et al., 2001; Wang et al., 2008) Because the operating conditions of a vehicle traveling in traffic are rarely available, its emissions and fuel consumption are often estimated from the design parameters, presumably operating under some selected average conditions However, in reality the operating conditions of any vehicle driving in urban areas are hardly controlled Traffic conditions, driving behavior, and frequency of vehicle maintenance and tune-ups are considered to be major factors, whereas the vehicle age also contributes to some extent Therefore, determination of the emissions and fuel consumption of a vehicle traveling in traffic is not an easy task On one hand, the values estimated from the design parameters operating under average conditions obtained from traffic data, such as average vehicle speed, may not be realistic On the other hand, it is extremely difficult to conduct actual measurements on several hundred thousand INTRODUCTION The Bangkok metropolitan area, with its large population (about 5.7 million in 2006) but insufficient mass transit systems, has suffered from severe air pollution caused by automobile emissions due to congested traffic conditions (Wibulswas, 1997) An effective way to alleviate the air pollution that has been adopted by several large cities where environmental problems are monitored is to issue regulations on the maximum allowable limits of exhaust gas emissions that a vehicle may release (Ergeneman et al., 1997) These limit levels vary from place to place depending on the standard of living, the affordability of costly but less-polluting technology, and the severity of traffic conditions Prior to setting the appropriate limits, current information about the amount of emissions and fuel consumption rates of vehicles traveling in the city must be determined *Corresponding author e-mail: supachar@siit.tu.ac.th 251 252 S TAMSANYA, S CHUNGPAIBULPATANA and B LIMMEECHOKCHAI ROAD ROUTE SELECTION method that has become more practical and widely used is the use of a traffic flow model to determine travel speeds from vehicle traffic flow data Traffic flow data generally contains the number of vehicles passing over sections of road along the main roads during a specific time interval at certain time periods of the day These data are normally collected by traffic authorities in most big cities The first step in the road route selection methodology starts with the analysis of these traffic flow data From the available vehicle flow data, a traffic flow model, the details of which are given in the next section, is applied to determine the representative travel speed of the cars along each section of major road routes considered By considering these travel speeds determined for all road sections of all major road routes, the distribution of vehicle speeds in the area can then be established Moreover, the average speed for each major road route can be estimated from the speeds of its individual road sections By averaging the speeds of the individual road sections, the mean speed of the vehicles can be determined The second step of the methodology is to select a few major road routes so that the distribution of vehicle speeds on all road sections along those selected major roads closely matches that of the major roads previously established The match between the distributions is confirmed by statistical parameters such as the variance and mean These few major road routes are therefore expected to cover all driving speed patterns occurring in the city and can be used as representative road routes for conducting real driving tests to collect the actual driving characteristics (i.e., speed versus time data) of vehicles, which will later be used for the construction of the driving cycle of vehicles traveling in the city 2.1 Selection Methodology A vehicle driving cycle for a city is constructed in order to represent the driving pattern that the vehicles would experience repetitively throughout their journeys when driving in the considered city Therefore, a typical driving cycle for a city must bedetermined from traffic data along the routes of those vehicles The number of such possible road routes can be enormous, and it is impossible to conduct actual measurements of the vehicle speed characteristics on all the road routes A possible way to resolve this problem is to select a number of road routes that represent the dominant traffic situations throughout the city A generic method for road route selection is therefore proposed in this study in order to determine the appropriate road routes for the collection of vehicle speed-time data In order to select road routes that can best represent the actual traffic, the real situations that occur along each route must be known Travel speed is a parameter commonly used to describe the real traffic situations (Traffic Research Board, 2000) Although travel speeds can be determined from observations on each road route in the area of interest, this is very costly and time-consuming An alternative 2.2 Traffic Flow Model The basic traffic flow model used for determining the average speed for each road section was introduced by Greenshield in 1943 (Dirks , 2003) It provides the relationship between traffic flow ( ), vehicle speed ( ), and vehicle density ( ), and can be expressed as: (1) q = k [ u – ( u2 / u ) ] where (vehicles per hour, veh/h) is the total number of vehicles that pass over a given point or section of a lane of roadway during a given time interval, (km/h) is the average traffic speed along the designated length of road, and (veh/km) is the density of the vehicles along the designated road Subscript refers to the free-flow traffic condition or the condition when there is a single car on the road and its speed is only limited by the speed limit set by the traffic authority In this equation, is the maximum free-flow speed that the car can travel freely when not inhibited by the presence of other vehicles Subscript refers to the traffic jam condition, and indicates that the road is completely blocked due to congestion and the speeds of all cars in the considered section are zero Hence, automobiles in city traffic One possible way to resolve this problem is to establish a generic driving characteristic or pattern for any vehicle traveling in the city under consideration The driving pattern provides the variation in vehicle speed over time for a certain period of travel (Tong , 1999) It can be interpreted in such a way that the vehicle would experience this driving pattern repetitively throughout its journey Statistically, it represents a typical driving pattern for the vehicle population of a city Moreover, as this driving pattern is assumed to be repeated continuously, it is a so-called “Driving Cycle” To date, no such driving cycle has been officially developed to represent traffic in Bangkok The driving cycle used for the assessment of exhaust emissions and fuel consumption of newly registered automobiles in Thailand (TISI, 2003) is based upon the standard driving cycle of the European Community As the driving pattern prescribed in the adopted cycle differs greatly from the actual traffic conditions in Bangkok, the results obtained from those tests may not reflect the real emissions and fuel consumption produced by the vehicles in Bangkok The objective of this study is therefore to develop a new driving cycle that can provide more realistic results for the assessment of the exhaust emissions and fuel consumption of vehicles traveling in Bangkok during peak periods Furthermore, the driving cycle can be adopted for tests of vehicles running in Bangkok in order to report the real world performance of vehicles in service Thus, the test report would provide information for Thailand’s energy and environmental agencies on how to set up proper national standards for the fuel consumption and exhaust emissions of motor vehicles et al et al q u k j f q u k f uf j DEVELOPMENT OF A DRIVING CYCLE FOR THE MEASUREMENT OF FUEL CONSUMPTION kj is the traffic jam density, which indicates the maximum number of vehicles that completely blocks traffic It can also be interpreted that the lower the value of kj is, the more traffic congestion occurs The traffic jam density kj can be determined from the relationship between the maximum traffic flow and the free-flow speed, which is expressed as (Mannering and Kilareski, 1998): k =4 qmax u (2) where qmax is the maximum traffic flow rate, or the maximum number of vehicles that can pass a given section during a specified period under prevailing roadway and traffic conditions (Wright, 1996; Mannering and Kilareski, 1998 and Traffic Research Board, 2000) In this study, the maximum traffic flow rate qmax for a road section is set to be equal to the maximum traffic flow rate that has ever occurred in that section, which can be found from the observed traffic flow data of that section It should be noted that two feasible values of average traffic speeds, u, calculated from Equation (1) can be obtained The higher speed can be interpreted as the freeflow conditions, and the lower speed represents the congested conditions The selection of the appropriate traffic speed must be considered with the queue length The queue length for each section is a normal traffic data recorded by traffic authority If the queue length is null (free-flow condition), then the higher speed must be selected j f 2.3 Determination of Representative Road Routes for Bangkok Traffic The traffic flow (q) data at each intersection in Bangkok used in this study were collected by the Traffic and Transportation Department (TTD, 2000) in 2000 for 66 road sections along 20 major road routes in Bangkok It is observed that the highest traffic volume occurs during the morning peak period (07:00-09:00 hr) In this period, the traffic volume exceeds the capacity of the road system (Leong et al., 2002) As a result, severe traffic congestion problems can be observed in the Bangkok area, which results in the highest exhaust emissions and fuel consumption during this period Therefore, collecting speed-time data in the morning peak periods could capture those 253 driving conditions that have the largest impact on exhaust emissions and fuel consumption The actual traffic flow, q, provided by TTD is the total number of vehicles per hour However, the number of vehicles per lane is needed for the calculation of the average travel speed of vehicles in each lane; therefore, it is assumed that there are equal numbers of vehicles in each lane Figure shows sample traffic flow data, q, for five road sections that are separated by six junctions along a part of a major road route called Sukhumvit Road during the morning rush period (07:00-09:00 hr) The road is located in the center of Bangkok and is well known for its severely congested traffic conditions for most of the day It is a two-way road with three lanes in each direction The data shown are obtained from the west-bound flow direction, which represents the flow of vehicles heading from residential zones in suburban areas to offices in the downtown area The vehicle counts were regularly conducted by TTD using manual traffic counters at each junction every 15 minutes for a 24-hour period The indicated number for each section is the whole year average value obtained during the specified time period of the day at the junction ahead of it For example, the traffic for Section is that averaged from the vehicle counting at Junction It should be noted that the numbers of vehicles flowing in and out of the lanes were so few that they are ignored in this study The model calculated results of average travel speeds, u, along those five road sections are illustrated in Table In the calculations, the free-flow speed, uf, for each section of Sukhumvit Road was taken to be 60 km/h, in accordance with the driving speed limit set for the inner city area The maximum traffic flow, qmax, for each section was obtained from the records of TTD Substituting uf and qmax into Equation (2), the value of jam density, kj, for each section can be found Using these values of kj with the data of q, the queue length, Lq, and the set speed uf, the value of u for each section is then determined by Equation (1) Finally, the average travel speed along the whole Sukhumvit Road, i.e., um, can be found using the arithmetic mean of the speeds of those five sections The results show that the jam density, kj, for the two sections closest to the city center (i.e., Sections and 5) are lower than the other three sections The values also suggest that the traffic in those Figure Schematic layout of a part of Sukhumvit Road with in-bound traffic flow rates in five considered sections.7 254 S TAMSANYA, S CHUNGPAIBULPATANA and B LIMMEECHOKCHAI Table Model calculated average travel speeds, u, on the five considered road sections along Sukhumvit Road for west-bound traffic during morning rush hours (07:00-09:00 hr) for the year 2000 Road section q Lq qm kj u (See Figure 1) veh/h m veh/h veh/km km/h 1593 123 2277 51 13.6 71 12.5 2109 272 3204 14 2290 110 3201 71 1331 50 2175 48 11.3 1266 300 2241 50 10.2 Average travel speed along Sukhumvit Road, um 12.3 areas were so congested that only 48 vehicles entering the sections per kilometer would cause a traffic jam Hence, their average travel speeds were lower and the cars would move more slowly along the roads approaching the downtown area The results of these average travel speeds along Sukhumvit Road agree with its well known congested traffic conditions in which the cars can move at low speeds ranging from 10.2 to 14 km/h during the morning rush hours The average travel speeds for the other 19 main roads can be determined in the same manner, and the mean speeds for these main roads can also be averaged from the corresponding road sections as shown in the Table Moreover, the observed values of mean speeds along these 20 main roads collected by TTD in 2000 during the morning rush hours are also displayed for comparison The observations were obtained by measuring the travel time of the survey cars when driving along the specified road route of a known total distance Differences between the calculated and observed average travel speeds can be expected since the mean observed value for each main road route was averaged from only six measurements undertaken periodically throughout the year The measurements may be too few to cover all the traffic situations occurring on these roads Nevertheless, as the discrepancies between the model calculated values and the observed values occur in both the greater and lower cases, and the closeness of the overall mean values averaged from all 20 main are within an acceptable range (Table 2), it can be preliminarily concluded that the simple traffic stream model can be used with confidence to determine the average travel speed along any road from its available traffic flow data More in-depth investigations could be carried out if higher accuracy results are required In order to establish the frequency distribution of the travel speeds for morning peak traffic, the calculated travel speeds of all 66 road sections in Table were classified into 13 ranges with an interval of km/h, as illustrated in Table and graphically depicted in Figure The frequency distribution for each speed range was determined by summing the number of vehicles per hour on the road sections which had travel speeds within that range It can be observed that about 70% of vehicles in Bangkok are driven at speeds of less than 20 km/h as a result of the congested traffic The highest frequency of travel speed is between 15 and 20 km/h, accounting for about 30% of the traffic Selection of a set of appropriate road routes for conducting real driving experiments was then carried out using the frequency distribution of vehicle travel speeds Consideration was paid to the agreement of the distribution of travel speeds of the selected road routes with that of the main road routes established above There are several randomly selected combinations of road routes that would give acceptable agreement A simple guideline based on the frequency distribution in Figure is that there must be one road route selected to represent each of the three travel speed ranges, i.e., 5~10 km/h, 20~25 km/h, and greater than 25 km/h Consequently, in order to satisfy these proportions, the other four road routes are required to have a range of travel speeds between 10~20 km/h Based on the guideline, seven road routes were then arbitrarily selected, as shown in Table Their frequency distribution was calculated and is also plotted in Figure in comparison with that for the whole main road routes The comparison shows good agreement between the frequency distributions The average travel speed for the seven selected roads, which is 16.9 km/h, is also close to that of the main roads, i.e., 16.5 km/h This indicates that these seven selected road routes (depicted in Figure 3) are adequate and appropriate to represent traffic situations of all the road routes in Bangkok Hence, they can be used for conducting the actual on-road measurements to collect the vehicle speed patterns (i.e., speed-time data) SPEED-TIME DATA COLLECTION To obtain the speed-time data for driving cycle construction, a vehicle equipped with an instrument for speed measurements must be driven along the seven selected road routes The type of vehicle selected was a passenger car with a capacity of no more than seven passengers This type accounts for the highest number of vehicles registered in Bangkok (Department of Land Transport, 2001), and is representative of vehicles that are driven in the morning from suburban residential areas to the commercial areas in the downtown In this study, the vehicle used was a 1993 Toyota Corona, with a 1.6 liter gasoline engine and a manual transmission The speed-time data collection was carried out using a real time logging system equipped on the selected passenger car traveling along the seven selected road routes under actual traffic Calibration of the speed-time datalogger was done before launching the selected vehicle to collect the speed-time data Good agreement was also found between the measured travel speeds obtained from the datalogger and the actual values that were obtained by dividing the known travel distance by an accurate stop watch The speed-time data were DEVELOPMENT OF A DRIVING CYCLE FOR THE MEASUREMENT OF FUEL CONSUMPTION 255 Table Model calculated travel speeds (km/h) on various road sections and comparisons of calculated average travel speeds with the TTD observed speeds along 20 main roads Model calculated travel speed, u, for each road section Model calcu- TTD No of (km/h) (its corresponding traffic flow rate (veh/h)) lated average Observed Differ* Main road road ence (Flow direction) sections travel speed travel speed (km/h) Road section (km/h) (km/h) Sathorn 6.7 6.7 10.5 −3.8 (east bound) (2245) Silom 7.5 8.8 8.2 7.3 +0.9 (east bound) (618) (2411) Jarernkrung 10.9 15.3 9.6 10.7 11.6 10.0 +1.6 (north bound) (832) (1077) (1222) (1427) Sukhumvit 13.6 12.5 14.0 11.3 10.2 12.3 12.5 −0.2 (west bound) (1593) (2109) (2290) (1331) (1266) Rajadamnern 11.6 13.6 12.6 11.2 +1.4 (east bound) (2421) (5024) Rachawithee 19.7 20.1 6.6 4.4 12.7 8.9 +3.8 (east bound) (3837) (673) (1274) (1274) Petchburi 13.5 16.4 9.3 11.6 12.7 11.4 +1.3 (west bound) (2726) (2613) (2465) (2065) Ramkhamhang 15.1 10.9 13.0 15.0 −2.0 (south bound) (3157) (1912) Payathai 7.3 16.7 13.8 18.8 14.2 10.5 +3.7 (south bound) (2026) (2652) (3093) (3199) 10 Praram6 10.1 21.0 12.0 14.4 11.7 +2.7 (south bound) (1478) (2968) (1473) 11 Ladprao 7.6 19.0 17.4 14.7 14.8 −0.1 (west bound) (877) (2419) (2749) 12 Sriayudhaya 18.1 12.5 15.3 13.1 +2.2 (east bound) (1595) (2180) 13 Praram4 20.8 16.1 11.1 28.8 8.8 9.8 15.9 10.0 +5.9 (west bound) (2953) (1834) (1946) (5651) (2411) (2848) 14 Phaholyothin 19.1 19.5 24.6 14.8 7.3 17.1 17.9 −0.8 (south bound) (3226) (4325) (6181) (2026) (2026) 15 Ratchadapisek 19.9 19.9 15.9 18.6 15.0 +3.6 (south bound) (4365) (2724) (3135) 16 Ramindra 21.9 20.4 21.2 24.2 −3.0 (west bound) (3238) (2956) 18.5 12.5 23.9 48.4 17 Jarunsanitwong 10.5 22.8 22.4 +0.4 (2278) (1962) (2863) (1909) (557) (south bound) 18 Pattanakarn 47.5 20.1 9.2 25.6 28.8 −3.2 (west bound) (1575) (2475) (1669) 19 Praram9 12.5 45.2 28.9 20.3 +8.6 (west bound) (2494) (2227) 20 Wipawadee 60.3 19.7 29.3 13.5 30.7 31.2 −0.5 (south bound) (8158) (5958) (10167) (3531) Total 66 Overall mean travel speed averaged from 20 main roads 16.5 (2.8)** 15.3 (3.0)** Note: The locations of these main roads are illustrated in Figure The value in the bracket is the standard error of estimate of the mean − * ** collected during the morning peak period from 7:00 a.m to 9:00 a.m in November and December 2003 The data from each road route were collected twice on Monday, Wednes- day, and Saturday in order to cover the range of driving patterns on weekdays and weekends Figure shows example results of speed-time data collected along Sukhumvit 256 S TAMSANYA, S CHUNGPAIBULPATANA and B LIMMEECHOKCHAI Table Frequency distribution of travel speeds of vehicles traveling in Bangkok during the morning rush hour (07:0009:00 hr) Range of Total number of vehi- Frequency Cumulative travel cles per hour which distribution frequency speed have travel speeds distribution (%) (km/h) within the range (%) 0