Robert Joumard

Influence of driving cycles on unit emissions from passenger cars

Abstract Small samples of petrol engine or diesel cars, equipped with or without catalysts, were tested over 36 driving cycles divided into four categories – standard cycles and three sets of cycles more representative of real-world driving conditions. The tests addressed standard gaseous pollutants and fuel consumption and also less frequently measured pollutant such as CH4. In the first part of this paper we examine cold emissions in order to assess the duration of the cold start impact and the representativity of the cold ECE15 cycle. Then unit emissions are compared over the four driving cycle families. As compared to representative cycles, the standardised cycles underestimate hot emissions by almost 50% for petrol engine cars and 30% for diesel vehicles. Conversely, the results obtained for the three representative cycle families are in relatively close agreement with each other – within approximately 10%. However, the cinematic properties of the three families differ. Finally, we demonstrate that weighting all emission data equally, not taking into account the weight of each cycle in overall traffic, introduces significant biases, particularly when plotting emission vs. average speed curves.

Hot passenger car emissions modelling as a function of instantaneous speed and acceleration

As part of the EC DRIVE programme, a study was carried out to determine the most important vehicle parameters that influence the emissions and fuel consumption of passenger cars. Emission measurements have been conducted in the three laboratories in France, Germany and UK on the basis of 14 driving cycles specially designed to cover the whole range of vehicle speed and acceleration in urban traffic. One hundred and fifty vehicles, representing the European 1 995 fleet, were tested, and the emissions of CO, HC, NOx and CO2 continuously recorded. Subsequently, a model was developed to calculate emissions during an urban trip as a function of the vehicle type and its instantaneous speed and acceleration. Average unit emissions are presented as a function of average speed and vehicle type. The model is given in the form of a two-dimensional junction with the variables, speed and speed times acceleration, for all vehicle types. An attempt to test this model with an on-board sampling system was made but without success. The paper briefly describes some typical applications.

Reliability of the current models of instantaneous pollutant emissions

Pollutant emissions and fuel consumption of passenger cars are usually assessed as a function of average as a function of average speed. Nevertheless a number of attempts were made to take into account the driving pattern using emission vs. instantaneous speed and acceleration models. Five quite similar models were developed in Europe. To which extent these instantaneous models are innovative as compared to conventional models? In a first step the various development stages of an emission-based model and the various associated errors are presented. Among the possible sources of error, we selected modelling-induced errors, enabling to compare rigorously the various model types in terms of performance. The analysis was performed using the Modem model, developed from the measurement results obtained over a sample of 150 vehicles, representative of French, English and German fleets, over 14 representative driving cycles under urban conditions. Average emissions as measured over these 14 cycles are compared to emissions calculated over same cycles using this model. Modelling errors range from -51% to +57% as a function of the considered cycle and the vehicle type. This inaccuracy is quite similar for the other four European models. This demonstrates the low reliability of the models used, which cannot be used to assess the impact of slight changes in the driving pattern, sometimes leading to completely false conclusions. These models are barely more precise than average speed based models. In a second step, a number of alternatives liable to improve the reliability of instantaneous models are contemplated: for example using another method for calculating acceleration, or increasing the number of speed and acceleration classes significantly. But this does not improve significantly the model reliability. Limited measurements performed on a catalyst vehicle demonstrated that very high engine loads, even if not frequent, play a significant role in emissions: sometimes they yield emission values a thousand times higher. It is therefore of prime interest to study them in a comprehensive manner. In addition, this demonstrates that each model should be developed from measurements carried out over a set of representative driving cycles under real-world driving conditions.

ACTUAL CAR USE AND OPERATING CONDITIONS AS EMISSION PARAMETERS: DERIVED URBAN DRIVING CYCLES

Abstract A large-scale experiment has been carried out within the European DRIVE Project to identify actual vehicle use conditions. Fifty-eight privately-owned cars — 13 models, in 6 European cities — were equipped with sensors and data acquisition systems and studied under actual use conditions with their own drivers during 1-month period. A wide range of variables were measured and continuously recorded in order to define engine and vehicle operating conditions. Vehicle and engine speeds, engine and ambient temperatures, and fuel consumption have been recorded at 1-s time intervals over 73 000 km and 8200 trips. The data obtained yielded very accurate information on the actual car use which provided a wide image of normal European driving. This database enabled the analysis of car use characteristics and operating conditions which probably influence pollutant emissions and fuel consumption: daily vehicle use, trip characteristics (trip length, duration, etc.), speed and accelerations used, engine running conditions (engine speeds, choke use, etc.), thermal conditions. Traffic conditions have been characterized through splitting recorded speed profiles into ‘kinematic sequences’, between successive stops. Factorial analysis and classifying techniques enabled characterization of these sequences and linking of the different sequence types. A set of driving cycles for realistic emission measurements has been drawn up using these data, representing the different traffic conditions and driving patterns observed, while taking into account the influence of the vehicle type, drivers behaviour and geographical location, as well as the detailed records of engine operations. Vehicle uses were very frequent and often short. Time spent at rest or at low speed is very significant. Short trips, low temperatures, accelerations, and more generally urban traffic conditions, caused significant increases in fuel consumption.

Representative Kinematic Sequences for the Road Traffic in France

This study aims at analyzing light vehicle traffic in France and at characterizing it by a set of speed profiles. A new approach is proposed introducing the notion of kinematic sequence and using different methods of data analysis. The first objective is to get satisfactorily summarized information on the structure of vehicle displacements. A set of data, recorded from an instrumented passenger car fleet for the EUREV study, is analyzed with data analysis processing. The great variety of the speed profiles collected means that the study is representative of the actual use of cars in France. Four sequence categories which feature specific types of traffic are shown. Consequently these sequences should lead to the measuring of fuel consumption and pollutant emissions representative of the actual uses, under appropriate laboratory conditions.

Analysis of PAH Emissions from Passenger Cars by High Resolution Shpol'skii Spectrofluorometry

Abstract Twenty-five passenger cars (10 conventional petrol engined cars, 10 vehicles equipped with a 3-way catalyst and 5 diesel engined vehicles) were tested on a chassis dynamometer. Exhaust gases were collected in a Constant Volume Sampling system using Teflon filter and XAD2 adsorber. Identification and quantification of PAHs were carried out by high resolution Shpolskii spectrofluorometry over two INRETS cycles (urban and road cycles) representative of real – world driving conditions under hot or cold start. The results obtained in μg per km exhibit for the three technologies: - the influence of average speed - the efficiency of catalyst, under hot and cold start - higher emissions by conventional petrol engined cars, particularly under cold start and low speed conditions.

Alternative short tests for inspection and maintenance of in-use cars with respect to their emissions performance

This paper presents the first results of a project aimed at evaluation of a number of short tests that can be alternatively used for Inspection and Maintenance of in-use cars emissions performance. For this purpose, a large number of in-use cars from four European countries was tested according to a test protocol that included a wide selection of short tests (idle and fast idle tests, a steady-state loaded test and short transient loaded tests), in addition to the legislated New European Driving Cycle and a number of real-world cycles. The test results were statistically analysed in a number of different combinations, with the objective to define a set of reasonable cutpoints, taking into account various criteria such as errors of commission, errors of omission, excess emitter identification rate and excess emission identification rate.

On-Board Emission Measurement of High-Loaded Light-Duty Vehicles in Algeria

Abstract A sample of eight private gasoline and diesel conventional light-duty vehicles (LDVs) in use with various ages, carrying a load of 460 kg, were tested on a representative trip in the traffic flow of the city of Blida to obtain emission factors representing the actual use conditions of Algerian LDVs. The gas sampling system (mini-constant volume sampling) as well as the analyzers are carried on-board the vehicle. Around 55 tests were conducted during 3 months covering more than 480 km under various real driving conditions. The mean speed downtown is about 16.1 km/hr with a rather low acceleration, an average of 0.60 m/sec2. For each test, kinematics are recorded as well as the analysis of the four emitted pollutants carbon dioxide, carbon monoxide, oxides of nitrogen, and total hydro-carbons. Emission factors were evaluated according to speed for each category of gasoline and diesel engines. The influence of some parameters such as cold/hot start, age of vehicle and its state of maintenance are discussed. Results are compared with the European database ARTEMIS for comparable vehicles. These measurements contribute to the development of unit emission of the vehicles used in Algeria, which are necessary for the calculation of emission inventory of pollutants and greenhouse gases from the road transportation sector. The unit emissions constitute a tool of decision-making aid regarding the conception of new regulations of vehicle control and inspection in Algeria and even in similar developing countries.

Air quality and urban space management

Abstract A typology of air pollution, the evolution of urban transport emissions and of air quality in urban areas allow us to list the three main urban pollutants today: nitrogen oxides, carbon monoxide and particulates. Then, various potential solutions in terms of vehicle technology, but mainly in terms of traffic management and restraints on vehicle use (e.g. public transport, reductions in traffic congestion, traffic concentration, speed reductions, traffic cell scheme in urban central areas, reduction in traffic volumes and urban road pricing) are presented and analyzed from French and mainly foreign examples, and assessed from an effectiveness standpoint in the air pollution and environmental field. A specific attention is paid to urban planning (densification, zoning giving up) in particular from the example of the Curitiba city in Brazil where a voluntarist and efficient policy has been adopted in this field.

Cold start emissions of traffic

Abstract CO, HC, NOx, particulate emissions and fueld consumption were measured on a chassis dynamometer for both hot and cold start. Three urban driving cycles were used, two ECE15 cycles for tuned and as received vehicles and one representative of the actual driving patterns. 51 cars (gasoline and diesel engines) were tested using this method. From these measurements and others made in Europe we are able to know the influence of ambient temperature on cold start emission rates and fuel consumption of passenger cars. In addition the actual operating conditions of 35 private cars operated normally by their owners were recorded in winter and summer all over France, over a total distance of 23000 km. The great number of short trips (40% less than 2 km) shows the importance of cold start. The modelling allows us to know the mileage percentage according to cooling water and ambient temperature. So we can calculate the cold mileage percentage according to trip length (the average percentage is 27% in France). These results allow us to model traffic cold start emissions for different national and local situation as regards the ambient temperature and the actual driving patterns. The additional emissions can be very high for some pollutants such as CO (30% in France) or VOC (46%).