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Byline: Patrik Soltic, Martin Weilenmann, Philippe Novak The investigation of several passenger car generations with gasoline engines shows that the emissions depend very strongly on the driving cycle. Official type approval cycles allow just very inaccurate predications about their real-world emissions. The measured gasoline vehicles have up to factor 11 higher real-life emissions than in type approval cycles. However, a clear reduction of real-world emissions can be seen over the different investigated generations of gasoline cars. In addition, it can be seen that the cold start emissions depend strongly on ambient temperature levels for all generations of cars and that the cold start accounts for an increasing part of the total pollutant emissions. As an extreme example, the cold start hydrocarbon emissions of Euro-3 cars at 20uC ambient temperature correspond approximately to those of 1,000 km driving with warm engines.

Byline: Peter Mattrel, Ana-Marija Vasic, Erika Gujer, Regula Haag, Martin Weilenmann The emission profile of volatile organic compounds (VOC) and the ozone-forming potential (OP) of the exhaust gas of six in-use motorcycles (four 4-stroke- and two 2-stroke-engines) were determined. The motorcycles were tested on a chassis dynamometer in a real-world driving cycle. The analysis involved the C2C12-hydrocarbons as well as the aldehydes and ketones. Additionally, the regulated THC and NOx emissions were measured according to the test procedure for type approval (ECE 40). Two vehicles did not fulfil the THC emission standard, whereas all vehicles met the requirements for NOx emission. The aromatic fuel components toluene and xylene, and the combustion products ethene and propene contributed most to the OP of the VOC emission. The highest OP was found with the 2-stroke engines. The VOC profile of the emissions varied with vehicle and driving conditions. The reactivity of the exhaust gas, defined as gram ozone per gram of non-methane organic gases (NMOG), increased with vehicle speed.

Byline: Delia Ajtay, Martin Weilenmann Emission models can be categorised into three categories: average speed models; traffic situation models, used at macro-scale or meso-scale level (national, regional, city level); and instantaneous (modal) models, useful at micro-scale level (street, vehicle level). To improve the existing instantaneous emission models, some preconditions must be fulfilled: the emission signals should be measured on a 10 Hz basis, due to their frequency content. Additionally, the transport dynamics from the engine to the analysers must be compensated by time-varying approaches. With these preconditions fulfilled, a new static instantaneous emission model is developed and the improvement in quality is checked by comparing it statistically with older models. A dynamic instantaneous model, able to include the transient generation of emissions, is subsequently created and the quality of prediction of engine-out emissions is determined. When a catalyst model is added, more accurate predictions of emissions for vehicles with after-treatment systems should be obtained.

Byline: Martin Weilenmann, Christian Bach, Claudio Rudy Instantaneous emissions measurements on chassis dynamometers and engine test benches are becoming increasingly normal for environmental emission factor calculation. Modern exhaust gas analysers allow measurement at a rate of one sample per second, thus creating the impression that the emissions information recorded reflects that precision. Normally, the time delay between the car and the analysers is considered to be constant and compensated for accordingly. In reality, this time delay varies by more than three seconds depending on the engine load. Moreover, emission peaks are smoothed by turbulence during transport. The analyser's dynamics smooth the signals even more. For example, an emission peak of one second is flattened to a three-second peak in raw gas measurement, and to a very low hill of about ten seconds in diluted gas measurement. If emissions measurements are to be correlated to actual driving conditions, the variable time delays and the smoothing must be compensated for. To achieve this, the time delay at a given time can be calculated by dividing the volume of the exhaust system by the actual exhaust flow. 'Smoothing' is compensated for by adopting a system theory-based approach. It can be described with a linear differential equation, which can be 'inverted' in an offline procedure.

Abstract: The emissions from hot driving conditions, in which the exhaust-after-treatment systems are working properly, continue to decrease, which is why the emissions of cold starts have gained in importance. Traffic emission models are used to estimate and predict vehicle fleet emissions and the air quality of countries, regions, cities, etc. In addition to the statistical input of fleet activities, these models are mostly based on the use of separate emission sub-models for hot driving and cold start driving. In reality, the cold start models are almost entirely empirical and of limited accuracy. In this work, a model is developed that is based on physical reasoning, i.e., it is based on energy balances. Because many details, such as the thermal conductivities and the engine control decisions, are unknown, the model must be able to address different simplifications. The model can be parameterized with as few as two tests per vehicle. It is applied to several car samples (six to eight vehicles each) of different technical generations and shows reliable prediction for any combination of the driving pattern (including gradient), the ambient temperature, the stop time before the ride and the duration of the ride (if shorter than the warm-up phase). [Copyright &y& Elsevier]

Mobile air conditioning (MAC) systems are the second-largest energy consumers in cars after driving itself. While different measurement series are available to illustrate their behavior in hot ambient conditions, little data are available for lower temperatures. There are also no data available on diesel vehicles, despite these being quite common in Europe (up to 70% of the fleet in some countries). In the present study, six representative modern diesel passenger cars were tested. In combination with data from previous measurements on gasoline cars, a new model was developed - EEMAC = Empa Emission model for Mobile Air Conditioning systems - to predict emissions from air conditioning. The measurements obtained show that A/C activity still occurs at temperatures below the desired interior temperature. The EEMAC model was applied to the average meteorological year of a central European region and compared with the US EPA MOBILE6 model. As temperatures in central Europe are often below 20 °C (the point below which the two models differ), the overall results differ clearly. The estimated average annual CO2 output according to EEMAC is six times higher than that of MOBILE6. EEMAC also indicates that around two-thirds of the fuel used for air conditioning could be saved by switching the MAC system off below 18 °C. [ABSTRACT FROM AUTHOR]

Abstract: Because of air quality problems, the problem of CO2 related greenhouse gas emissions and shortage of fossil fuels, many vehicles with gaseous fuels (CNG, biogas, hydrogen, etc.) are under research and development. Such vehicles have to prove that both their exhaust emissions and their overall system emissions (including running loss) remain below certain safety limits before they can be used in practice. This paper presents a cost-effective way of monitoring such system emissions from hydrogen or other gaseous fuel powered vehicles within an air-conditioned chassis dynamometer test cell, as commonly used for low ambient emission tests on gasoline vehicles. The only additional equipment needed is a low-concentration sensor for the gas of interest (e.g. hydrogen). The method is based on concentration measurements and a dynamic mass balance model. It is shown by a real experiment that very low emissions can be recorded. Additionally, error bounds and sensitivities on different parameters such as air exchange ratio are quantified. [Copyright &y& Elsevier]

Passenger cars are the primary means of transportation in Europe. Over the past decade, a great deal of attention has therefore been paid to reducing their emissions. This has resulted in notable technical progress, leading to unprecedentedly low exhaust emissions. In the meantime, emissions from motorcycles have been ignored due to their subordinate role in traffic. Even though the motorcycle fleet is small in comparison with the car fleet, and logs lower yearly mileage per vehicle, their contribution to traffic emissions has become disproportionately high. Exhaust emissions of CO, HC, NOx, and CO2 from 8 powered two-wheelers were measured and compared to previous measurements from 17 gasoline-powered passenger cars performed at EMPA with the aim of ascertaining their relevance. Using exhaust emission ratios from both vehicle types, comparisons based on mean unit, mean yearly, and fleet emissions are considered. Present-day after treatment technologies for motorcycles are not as efficient as those for cars. A comparison of mean unit emissions shows that motorcycles exceed cars in NOx emissions. All comparisons reveal a significant HC ratio, to the detriment of two-wheelers. Overall, the relevance of emissions from powered two-wheelers is not negligible when compared with modern gasoline-powered passenger cars. [ABSTRACT FROM AUTHOR]