The analysis of the PEMS measurements of the exhaust emissions from city buses using different research procedures

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1 The analysis of the PEMS measurements of the exhaust emissions from city buses using different research procedures Jerzy Merkisz, Jacek Pielecha, Pawel Fuc, Piotr Lijewski Poznan University of Technology, Institute of Internal Combustion Engines and Transport -9 Poznan, ul. Piotrowo, Tel. +8 7, Fax: +8 {jerzy.merkisz, jacek.pielecha, pawel.fuc, Abstract The paper discusses the possibilities of measurement of the exhaust emissions generated by city buses operating in public transit. The currently used methods of exhaust emission measurement under laboratory conditions on engine test beds do not entirely reflect the varied driving conditions under which the vehicles are operated. The paper presents the results of the inuse exhaust emission measurements performed on city buses using a Portable Emissions Measurement System (PEMS). The paper focuses on the road tests methodology as well as the interpretation of the obtained results. analyzer received data directly from the OBD system and a GPS. Using the portable system an emission level of CO, HC, NO x, CO with the resolution of second was performed as well as the variations in the engine speed and torque the parameters obtained from the vehicle OBD (CAN SAE J99) and then used to calculate the engine unit energy. The recording of the geographical location (GPS) enabled a visualization of the trajectory and the calculation of the length of the road portions [ 7]. I. INTRODUCTION The paper discusses the possibilities of measurement of the exhaust emissions generated by city buses operating in public transit. The currently used methods of exhaust emission measurement under laboratory conditions on engine test beds do not entirely reflect the varied driving conditions under which the vehicles are operated. The paper focuses on the road tests methodology as well as the interpretation of the obtained results. The results of this study is the comparison of the on-road exhaust emissions according to measuring methods: () methodology, () methodology based on the measurement of work during the test and () author s method: methodology comprising the whole driving tests. II. METHODOLOGY The objects of the research were modern city buses: a conventional and a parallel hybrid bus used by the Poznan bus operator. The exhaust emission tests were carried out on a distance of several dozen kilometers on a highly congested bus route. The tests aimed at determining of the unit exhaust emissions of the tested objects and at the same time constituted a basis for the evaluation of the research method determined in the (Not-to-Exceed) [] on-road tests as per the 8/ standard [] (Fig. and Table I). During the tests, the exhaust emissions were measured with a portable emission analyzer Semtech DS by Sensors (the equipment is EU 8/ and USA CFR compliant) []. A portable Semtech DS was used for the emission measurements. The device allowed a measurement of the fuel consumption and emission level. The central unit of the Fig.. The view of the measuring equipment (exhaust emission measurement unit Semtech DS) fitted in the bus during the tests. Parameter TABLE I TECHNICAL DATA OF THE TESTED BUSES Conventional bus (diesel engine) Hybrid bus (diesel engine + electric engine) Engine type DAF PR 8 S Cummins ISB Displacement [cm] 9 7 Power max 8@ Torque max [Nm@rpm] 7@ 7 7@ 7 Emission standard Euro Euro Transmission VOITH DIWA 8. ALLISON Ep Vehicle weight [kg],7 7,8

2 III. EMISSION TESTS RESULTS AND ANALYSIS The authors have carried out in-use exhaust emission tests (CO, HC, NO x and CO performed under actual traffic conditions) on a selected bus route on a conventional bus and a hybrid bus. The tests were repeated several times but for the analysis presented in this paper two most representative tests were selected. The obtained data served to determine the unit emission of the said exhaust components calculated according to different research tests. The results of this study is the comparison of the on-road exhaust emissions according to measuring methods: () methodology, () methodology based on the measurement of work during the test and () author s methodology [8]: methodology comprising the whole driving tests.. Method The test, as defined in CFR 8.7-7, establishes an area ( control are under the torque curve of an engine where emissions must not exceed a specified emission cap for a given pollutant (Fig. ). A controversial issue is the applicability of the limits to the real-world driving. In order for standards to apply, the engine needs to remain within the zone (limits include operation at a minimum of % of rated power) for at least seconds. n idle n %ESC n hi Torque min bound % max power Torque max Torque, M [Nm] 8 Control Area Concerns arose that performing this action could prove to be difficult, as each time the driver removes the foot from the accelerator pedal, or shifts gears on vehicles with manual transmission, the engine leaves the zone (Fig. and Fig. ). emissions results are computed for each thirty second period of continuous operation. brake-specific emissions are computed by summing the total mass of emissions in grams and dividing by the total work (kwh) for each of these thirty second periods of continuous operation. CO [g/s] NOx [mg/s] CO [mg/s] HC [mg/s] Vehicle speed, V [km/h] 7 7 HC [mg/s] CO [mg/s] NOx [mg/s] CO [g/s] Vehicle speed [km/h] 8 7 Engine speed, n [rpm] n idle n %ESC n hi Torque min bound % max power Torque max Torque, M [Nm] 8 Control Area Engine speed, n [rpm] Fig.. The course of the combustion engine operation with the test measurement limitations marked: conventional bus, hybrid bus. - - Fig.. Exhaust emission and the course of the bus speeds with the work marked as per the requirements conventional bus. The calculated values of the unit emission in the urban drive according to the method were as follows (Fig. ): for a bus fitted with a conventional powertrain CO = = 7 g/kwh, CO =.7 g/kwh, NO x =.7 g/kwh and HC =. g/kwh. for a bus fitted with a hybrid powertrain CO = = 9 g/kwh, CO =. g/kwh, NOx =. g/kwh and HC =.7 g/kwh.

3 CO [g/s] NOx [mg/s] CO [mg/s] HC [mg/s] Vehicle speed, V [km/h] 7 7 HC [mg/s] CO [mg/s] NOx [mg/s] CO [g/s] - Vehicle speed [km/h] 8 - Fig.. Exhaust emission and the course of the bus speeds with the work marked as per the requirements hybrid bus. CO [kg/kwh]; CO, NOx, HC [g/kwh] CO [kg/kwh]; CO, NOx, HC [g/kwh] CO CO NOx HC CO CO NOx HC 7 During the testing of the conventional bus the time share of the operation meeting the conditions was %, but only measurement windows could have been distinguished lasting a bit over s. For the hybrid vehicle the time share was 9% and measurement windows could have been distinguished (the characteristics of the obtained results Table II). Exhaust emissions [g/kwh] TABLE II THE CHARACTERISTICS OF THE OBTAINED RESULTS COMPLIANT WITH THE REQUIREMENTS Avg. Conventional bus (diesel engine) Max Std. Dev. Avg. Hybrid bus (diesel engine + electric engine) Max Std. Dev. CO CO NO x HC UE 8/ Method The emissions shall be integrated using a moving averaging window method, based on the reference work. The principle of the calculation is as follows: The mass emissions are not calculated for the complete data set, but for sub-sets of the complete data set, the length of these sub-sets being determined so as to match the engine work measured over the reference laboratory transient cycle. The moving average calculations are conducted with a time increment Δt equal to the data sampling period. These sub-sets used to average the emissions data are referred to as averaging windows. The duration of the averaging window is determined by: W(Δt) W ref, where W(Δt) is the engine work measured between the start and time t (in kwh), W ref is the engine work for the WHTC (in kwh). In order to realize that task the authors needed to estimate the value of work in the WHTC test for the conventional and hybrid buses. In order to determine work in the WHTC test we need to know the course of engine speed and the torque in this cycle. In order to determine the actual engine speeds and loads a denormalization was carried out of the engine operating parameters. Its first stage is the determination of the characteristics of the full power for each of the engines. Based on that, the actual parameters (engine speed and torque) of the engines were calculated, according to the methodology given in regulation 8/ (Fig. ). The estimated value of work of a conventional engine in the WHTC test was. kwh, and the engine used in the hybrid vehicle 8. kwh. Fig.. On-road unit exhaust emission (actual traffic conditions) as per the method: conventional bus, hybrid bus.

4 Torque, M [Nm]; Engine speed, n [rpm] Torque, M [Nm]; Engine speed, n [rpm] Engine speed Torque Cumulative work 9 8 Engine speed Torque Cumulative work 9 8 Fig.. WSHC cycle, engine speed and torque (after denormalization): conventional bus, hybrid bus. CO [kg/kwh]; CO, NOx, HC [g/kwh] CO [kg/kwh]; CO, NOx, HC [g/kwh] CO CO NOx HC.9.. CO CO NOx HC Fig. 7. On-road unit exhaust emission (actual traffic conditions) as per the method determined in EU regulation 8/: conventional bus, hybrid bus..7 Comulative work, W [kwh] Comulative work, W [kwh] Knowing the reference values of work for the tested vehicles the unit exhaust emission was summed up only in the measurement windows for which the total engine work exceeded the previously given values. For the conventional vehicle the number of all proper measurement windows in the whole test was 87 (the time of duration of the measurement window was a range from 99 s to s) and for the hybrid vehicle 9 (the time of duration of the measurement window was a range from 9 s do s). The results presented in Figure 7 are averaged values with the standard deviations marked for each exhaust components.. Author s Method The values of the unit exhaust emissions in the next method were determined using the data collected during the whole bus test drive (separately for the conventional and hybrid vehicles). These results reflect the actual, in-use operating conditions and at the same time constitute a basis for comparing the ecological nuisance of the city transit. On this basis we can classify various bus routes and the possibilities of replacing of the conventional buses with hybrid ones (Fig. 8). CO [kg/kwh]; CO, NOx, HC [g/kwh] CO [kg/kwh]; CO, NOx, HC [g/kwh] CO CO NOx HC.7.. CO CO NOx HC Fig. 8. The results of the unit emission tests calculated with the use of data recorded while the vehicle was in operation on the bus route: conventional bus, hybrid bus..

5 IV. CONCLUSIONS Having performed the analysis the authors obtained varied values for individual exhaust components depending on the applied method of calculation (Fig. 9): CO [kg/kwh]; CO, NOx, HC [g/kwh] CO [kg/kwh]; CO, NOx, HC [g/kwh] ) for conventional bus: CO : g/kwh (at variability of 7 g/kwh), CO:. g/kwh (at variability of.7.98 g/kwh), NO x :. g/kwh (at variability of..7. g/kwh), HC:. g/kwh (at variability of..8 g/kwh), ) for hybrid bus CO : 8 g/kwh (at variability of 9 9 g/kwh), CO:.8 g/kwh (at variability of.. g/kwh), NO x :.7 g/kwh (at variability of..7 g/kwh), HC:. g/kwh (at variability of..7 g/kwh) method - UE 8/ method - Authors method..8.7 CO CO NOx HC method - UE 8/ method - Authors method CO CO NOx HC The highest values of the unit emission were obtained according to the calculation method, and the lowest according to the method using all the data recorded during the whole driving test. Comparing the obtained test results of the unit emissions for the investigated buses we need to confirm great similarity between the obtained results. It is, however difficult to point to the method that fits the comparative criterion most when measuring the exhaust emissions with the portable emissions analyzers (PEMS). The method determined by is very good for heavy-duty vehicles operating at high loads in the expressway cycle. The methodology introduced by the EU is based on values that need to be known prior to developing the tests (e.g. reference work in the WHSC test). ACKNOWLEDGMENT This work has been financed from the resources for science for the years 9- as a research project No. NR. REFERENCES [] Regulations Commission: Regulation (EU) No 8/ of May implementing and amending Regulation (EC) No 9/9 of the European Parliament and of the Council with respect to emissions from heavy duty vehicles (Euro VI) and amending Annexes I and III to Directive 7//EC of the European Parliament and of the Council,. [] United States Environmental Protection Agency, Control of Emissions of Air Pollution from and Later Model Year Heavy-Duty Highway Engines and Vehicles; Revision of Light-duty Truck Definition, CFR Parts 8 and 8, 999. [] T. Bougher, I.A. Khalek, S. Trevitz and M. Akard, Verification of a Gaseous Portable Emissions Measurement System with a Laboratory System Using the Code of Federal Regulations Part, SAE Technical Paper Series --9,. [] H. Jehlik, Challenge X 8 Hybrid Powered Vehicle On-Road Emissions Findings and Optimization Techniques: A Year Summary, Sensors th Annual SUN (SEMTECH User Network) Conference, September 8. [] P. Bonnel, M. Weiss and A. Provenza, In-use Emissions Requirements in the New and Future European Motor Vehicle Emissions Regulations: State of Play, In: 8th Annual SUN Conference, Ann Arbor. [] K.C. Johnson, T.D. Durbin, D.R. Cocker, J.W. Miller, R.J. Agama and N. Moynahan, On-Road Evaluation of a PEMS for Measuring Gaseous In-Use Emissions from a Heavy-Duty Diesel Vehicle, SAE Technical Paper Series 8--, 8. [7] L. Rubino, P. Bonnel, R. Hummel, A. Krasenbrink, U. Manfredi, G. De Santi, M. Perotti and G. Bomba, PEMS Light Duty Vehicles Application: Experiences in downtown Milan, SAE Technical Paper Series 7--, 7. [8] J. Merkisz and J. Pielecha, The On-Road Exhaust Emissions Characteristics of SUV Vehicles Fitted with Diesel Engines, Combustion Engines, No.,. Fig. 9. The values of unit emissions obtained during the on-road tests and with different calculation methods: conventional bus, hybrid bus: methodology, methodology based on the measurement of work during the test, author s method: methodology comprising the whole driving tests.