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A New Method to Calculate Instantaneous Vehicle Emissions using OBD Data

A New Method to Calculate Instantaneous Vehicle Emissions using OBD Data
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  Page 1 of 18 2010-01-1289 A new method to calculate instantaneous vehicle emissions using OBD data Fernando Ortenzi CTL, Centre for Transport and Logistics, Sapienza University of Rome – Italy Maria Antonietta Costagliola Istituto Motori, National Council of Research, Naples, Italy Copyright © 2010 SAE International ABSTRACT The actual type approval procedure of vehicles, based on a fixed driving cycle for all the vehicles (NEDC), is not representative of their real on-road usage: the driving style and its influence on consumption and emissions cannot be neglected. The on road impact of vehicles on their real use is not known and it is difficult to measure (the PEMS are expensive, have big volume and mass and need continuous maintenance); the objective of this work is to develop a methodology to calculate in real time the energy and environmental impact of spark ignition vehicles, using the onboard sensors of the vehicle and emissions models to calculate them. An onboard instrumentation able to communicate with the electronic system of the vehicle (OBD/CAN) was developed to collect all the sensor data installed on a vehicle: those values are used as input values to the emissions models of CO 2 , CO, HC and NO x  developed in the present work. The CO 2  and CO have been calculated using a chemical equilibrium combustion model with 6 combustion products, with the equilibrium temperature used as a calibration constant. HC and NOx, produced during transients, are assumed to be dependent from the accelerator pedal gradient, but during engine cold start also from the catalyst temperature. To validate the models, a spark ignition hybrid vehicle, the Honda Civic Hybrid has been tested on a chassis dynamometer running the three Artemis driving cycles. The emissions have been measured with the CVS (taken as reference) and with a portable emission analyzer, (Horiba OBS 1300), used for comparison with the models. The results shows that the values calculated by the models are comparable with those measured by OBS, but for HC and NO x  are better because the OBS gave inaccuracies due to its high minimum resolution. INTRODUCTION Although the recent technological improvements in engine, fuel and after-treatment devices, road transport is still responsible for air pollution in urban area due to increasing number of circulating vehicles and their relative travelled distances. The actual European type approval procedure for passenger cars and light-duty vehicles fixes standard limits for exhaust pollutants to be respected during the execution of a normalized driving cycle. This kind of procedure is not representative of the real on-road use of vehicles, characterized by a more dynamic speed profile: a fixed driving cycle, equal for all the vehicles penalizes low power-weight ratio vehicles that see the driving cycle more hard to execute than vehicles with higher ratios and does not take  Page 2 of 18 account for the driving style; the influence of driving style to the emissions in driving the same vehicle is not negligible [1,2]. In the last years, a lot of on-board pollutant measurements at the exhaust of vehicles was carried out in order to assess the real emission behaviour: the high costs of portable emissions analyzers (PEMS), their continuous maintenance and calibrations, the fragility of the components and the weight and the encumbrance do not allow big acquisition campaigns. From previous works [3,4] it has been possible to develop a new approach for real time measurement of the engine and vehicle parameters from OBD connector while, in conjunction with an exhaust analyzer (Horiba OBS 1300, named OBS in this paper), have been performed on-road acquisition campaigns on conventional vehicles and hybrids [1,2,4]. In [1,2] different drivers have driven 3 Honda cars (two hybrids and one conventional) on the same path and big differences in terms of emissions produced have been observed from driver to driver. This difference is due to how the driver uses the accelerator pedal and in particular to its variation or the standard deviation. Also the conditions in which the thermal engine produces the highest levels of emissions have been investigated (cold start, full load and transients) [4] and also the optimal conditions (steady state) in which there are very low values of NO x , CO and HC produced. Starting from a previous work [3] in which a instrumentation capable to collect in real time all the sensors data from the electronic system of vehicles (OBD) was developed, the objective of the present work is to develop a methodology to calculate the instantaneous values of emissions at the exhaust of spark ignition vehicles by using emission models that have as input such OBD data. In literature, due to the fact that the vehicle electronics and its standardization have been developed only in recent years, the calculation of emissions is based using only the speed value [5], treating the thermal engine as a “black box” and not knowing all the instantaneous parameters. In this work the characteristic engine parameters are used to calculate the emissions. With a embedded pc and a software to collect data from the OBD diagnostic port it is possible to release an instrumentation more compact, economic and that does not require maintenance able to calculate the energetic and environmental impact of vehicles also in remote. Then it could be possible to make big acquisition campaigns, to monitor fleets of vehicles in their real use without modifications of the vehicle (in terms of weight and encumbrance) and with low costs. This can also be the starting point for a new approach of the type approval procedure of vehicles, based on a pre-homologation test, substituting it with a constant real time monitoring of the vehicle emissions and for example, tax calculation on the basis of the real pollution produced. The present work is organized: a first part in which the onboard instrumentation is reported together with the improvements respect to that described in [3], then a second part describes the developed emission models. The models are also calibrated and validated on a chassis dynamometer, comparing the experimental measurements performed by two different gas analyzers (a PEMS and an analytical one) with the predicted values of model. In the last part of the paper are reported the conclusions. THE ONBOARD INSTRUMENTATION All the European vehicles equipped with a lambda sensor, so all the vehicles from 1993 have an electronic system to control the fuel injection and then a diagnostic system to read sensor data and to store trouble codes. In Europe, starting from 2001 (in USA from 1996) with the Euro III standard, all the vehicles have also to supply in a standardized way, from a standardized connector, a common set of engine parameters so it could be  Page 3 of 18 possible to connect to all the vehicles with a unique hardware interface and with a unique communication protocol. The standards of interest to communicate with the electronics of vehicles are [6]: •   SAE J1962; in this standard is defined the shape and the number of pins of the OBD connector that is located within the cab of every vehicle; •   SAE J1850 (VPW e PWM); standard for the hardware interface generally compliant with American vehicles (Ford and General Motors); while; •   ISO 9141-2 and SAE14230-4 (KWP2000): are the standard for the interface compliant with European and Asiatic vehicles; •   ISO 15765-4; is the standard for vehicles equipped with CAN-bus; •   SAE J1979: in this document is reported the communication protocol to connect, using the interfaces to, to the vehicles and read the engine parameters. The parameters, collected from the instrumentation, with high frequencies (2-5 Hz) are: vehicle speed, air/fuel ratio, the intake airflow, rpm, engine load, accelerator pedal position, lambda sensor voltage, catalyst temperature, Close/Open Loop information, absolute load (volumetric efficiency), intake air pressure, EGR and ignition advance. There are also some other parameters, with slow temporal variation, collected every 30 seconds: the intake air temperature, the coolant temperature, the ambient temperature and pressure, the tank fuel level and the battery voltage.  Page 4 of 18 Fig. 1 Screenshot of the acquisitioA pc with an OBD interface and a Gscreenshot of the acquisition softwarnumber of available parameters coulsystem installed onboard. Also the acelectronic system installed on the vehexample have a bus speed of 500 kb/ with a frequency up to 100 Hz, more software to collect the engine parameters frvehicle. S can store such data with a software [3] as i with the engine parameters collected on a H be different from vehicle to vehicle and it is quisition speed is dependent from the protocicle, but also from the model of the interface and with a CAN-USB adapter it is possible than sufficient for the present work. m the OBD connector of the n Fig. 1 in which there is a onda Civic Hybrid. The dependent to the electronic l adopted and then from the used: the can-bus, for   to collect all the above data  Page 5 of 18 Other characteristics of the onboard imodem and notify possible trouble cusing the Wi-Fi communication and twithout any control from technicians vehicles monitored. THE EMISSION MODELS Starting by OBD parameters, a set of of CO, CO2, NOx and HC. An additipollutants emitted at the exhaust of vThe emissions of modern spark ignitimapped in three-dimensional steady exception of the full loads, the emissiparameters that vary rapidly with timtransients are responsible of producti CO AND CO 2   To calculate the CO and CO2 a simpl[7,8]. The first assumption is that the The combustion products are six: CO ig. 2 The On Board instrumentation nstrumentation are (Fig. 2), the possibility to des and to upload automatically all the onbo he SFTP protocol. The onboard unit is then a or operators: it is so possible to make big ac models was developed in order to calculate tonal gas transport model allow to calculate hicle. In the following, each model will be don vehicles, equipped with O 2  sensors and th tate engine maps because in those conditionons produced are very low [13], so in this w: throttle pedal gradients and air fuel ratio fon of CO, NO x  and HC. e combustion model with the hypothesis of c fuel is an hydrocarbon of the form C H O N  α β γ   2222 ,,,,,  H O N O CO H   with the following equili communicate with a GSM ard collected data to a server ble to work in automatic uisition campaign with many   he volumetric concentrations ass emissions of each etailed. ree way catalysts cannot be (or in Close Loop), with the rk they are in function of r example that during hemical equilibrium is used δ   and air is 22 0.790.21  N O ⋅ + ⋅ . brium reaction
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