Worldwide Harmonized Light Vehicles Test Procedure Research Articles

Aerodymamic Simulation of a Standalone Rotating Tread Tire

The aerodynamics of a rotating tire can contribute up to a third of the overall aerodynamic force on the vehicle. The flow around a rotating tire is very complex and is often affected by smallest tire features. Accurate prediction of vehicle aerodynamics therefore requires modeling of tire rotation including all geometry details. Increased simulation accuracy is motivated by the needs emanating from stricter new regulations. For example, the upcoming Worldwide harmonized Light vehicles Test Procedures (WLTP) will place more emphasis on vehicle performance at higher speeds. The reason for this is to bring the certified vehicle characteristics closer to the real-world performance. In addition, WLTP will require reporting of CO2 emissions for all vehicle derivatives, including all possible wheel and tire variants. Since the number of possible derivatives can run into the thousands of models, their evaluation in wind tunnels is not be practically possible. Therefore, simulations are the only alternative especially, since their use is allowed by WLTP. As a first step in order to meet these escalating demands, the current study uses a Lattice Boltzmann method (LBM) based computational fluid dynamics (CFD) solver using an immersed boundary method (IBM) based approach to simulate and validate a standalone rotating treaded tire. Simulated wake plane prediction results are in good agreement with experimental wake plane measurements. Effect of tire loading on wake results is also discussed.

Analysis of fuel consumption and pollutant emissions of regulated and alternative driving cycles based on real-world measurements

Discrepancies between real-world use of vehicles and certification cycles are a known issue. This paper presents an analysis of vehicle fuel consumption and pollutant emissions of the European certification cycle (NEDC) and the proposed worldwide harmonized light vehicles test procedure (WLTP) Class 3 cycle using data collected on-road. Sixteen light duty vehicles equipped with different propulsion technologies (spark-ignition engine, compression-ignition engine, parallel hybrid and full hybrid) were monitored using a portable emission measurement system under real-world driving conditions. The on-road data obtained, combined with the Vehicle Specific Power (VSP) methodology, was used to recreate the dynamic conditions of the NEDC and WLTP Class 3 cycle. Individual vehicle certification values of fuel consumption, CO2, HC and NOx emissions were compared with test cycle estimates based on road measurements. The fuel consumption calculated from on-road data is, on average, 23.9% and 16.3% higher than certification values for the recreated NEDC and WLTP Class 3 cycle, respectively. Estimated HC emissions are lower in gasoline and hybrid vehicles than certification values. Diesel vehicles present higher estimated NOx emissions compared to current certification values (322% and 326% higher for NOx and 244% and 247% higher for HC+NOx for NEDC and WLTP Class 3 cycle, respectively).

Introducing a New Emissions Certification Procedure for European Light-Duty Vehicles: Monte Carlo Simulation of the Potential Effect on Fleet Carbon Dioxide Emissions

Initiatives to reduce carbon dioxide (CO2) emissions from light-duty vehicles have been the cornerstone of European policy for curbing greenhouse gas emissions from road transport in past decades. The political approach has shown its effectiveness in recent years. However, the use of an outdated test procedure to measure the progress in reducing fuel consumption and CO2 emissions jeopardizes these efforts. For this reason, the European Commission is committed to introducing, in the shortest possible time, the new Worldwide Harmonized Light Vehicles Test Procedure (WLTP), developed through the United Nations Economic Commission for Europe, to reduce the gap between type approval and real-world figures on CO2 emissions. The introduction, however, requires the adoption of the CO2 targets set by the relevant European regulations. The approach selected by the European Commission for dealing with this issue required the development of a technology-oriented vehicle simulation model, CO2MPAS, which has been extensively validated against simulated and real data to demonstrate its capacity to capture the differences between the two certification procedures. In the present study, CO2MPAS is used to analyze the possible effects of the introduction of WLTP in the European vehicle market in terms of reported CO2 emissions. An approach based on Monte Carlo sampling has been adopted because of the lack of detailed vehicle information. The differences in estimated CO2 emissions are compared and discussed. Results indicate the accuracy and robustness of CO2MPAS in reproducing CO2 emissions at the fleet level. The results also indicate an increase in global CO2 emissions from existing passenger cars on the order of 10 g/km.

ANALYSIS OF MEASUREMENT ERRORS OF CVS METHOD USED FOR TESTS OF POLLUTANT EMISSIONS FROM LIGHT-DUTY VEHICLES

The test procedure for the pollutant emissions from light-duty vehicles is currently under verification carried out at the international level. For this purpose, GRPE (Groupe des rapporteurs sur la pollution et energie) – the body developing UNECE regulations proposals has set up a task group WLTP (Worldwide harmonized Light vehicles Test Procedure) which is supposed to prepare a new GTR (Global Technical Regulation) relating to this procedure. The development of light-duty vehicles, leading to the reduction of pollutants emissions, caused the increase of the requirements for their test procedure. A large number of factors associated, inter alia, with the test equipment affects its accuracy, repeatability and reproducibility. In the ongoing analysis attention is paid even to factors, which affect test results in a relatively small way, and which have been overlooked yet. One of the problems to which attention is paid is the impact of pollutant concentration in the dilution air in the CVS (constant volume sampler) system on test results. The CVS principle is accepted as the standard method to determine light-duty vehicle exhaust emissions on chassis dynamometer test cells worldwide. It was introduced in the early 1970s. One of its drawbacks is that it introduces an error resulting from the fact that the contractual DF dilution factor, rather than the actual dilution ratio DR, is used for the correction of concentration measurement results. The article discusses this error for different type of engines used in light-duty vehicles and different pollutants subject to measurements.

An Assessment of Emissions from Light-Duty Vehicles using PEMS and Chassis Dynamometer Testing

From 1 September 2014 new car types in the EU must meet ‘Euro 6’ emissions requirements. The ‘New European Driving Cycle’ (NEDC) is currently the main test for this, but the European Commission intends to also introduce PEMS (Portable Emissions Measurement Systems)-based procedures to ensure that emissions are well controlled in real use. ‘Random Cycles’ have also been considered and remain a possible option for ‘real world’ particle number measurement. At the same time, the UN Working Party on Pollution and Energy (GRPE) has developed the new Worldwide harmonized Light vehicles Test Procedure (WLTP) that is expected to be adopted in the EU in the near future. To identify and understand the differences in emissions that may arise between these various methodologies, AECC has conducted some initial tests on two modern light-duty vehicles. Chassis dynamometer emissions tests were conducted over the NEDC, the Common Artemis suite of test cycles (CADC), the new Worldwide Light-duty Test Cycle (WLTC - the test cycle for WLTP) and a set of cycles produced by a Random Cycle Generator based on ‘short trip’ segments from the EU database used to construct WLTC. A Portable Emissions Measurement System (PEMS) was used to measure emissions during real driving over pre-selected routes. The test results show that there can be substantial differences for some pollutants measured as ‘real driving emissions’ (RDE) using PEMS equipment, compared to the test cycles.

Hybrid-Electric Vehicle with Natural Gas-Diesel Engine

In this paper we demonstrate the potential of combining electric hybridization with a dual-fuel natural gas-Diesel engine. We show that carbon dioxide emissions can be reduced to 43 gram per kilometer with a subcompact car on the New European Driving Cycle (NEDC). The vehicle is operated in charge-sustaining mode, which means that all energy is provided by the fuel. The result is obtained by hardware-in-the-loop experiments where the engine is operated on a test bench while the rest of the powertrain as well as the vehicle are simulated. By static engine measurements we demonstrate that the natural gas-Diesel engine reaches efficiencies of up to 39.5%. The engine is operated lean at low loads with low engine out nitrogen oxide emissions such that no nitrogen oxide aftertreatment is necessary. At medium to high loads the engine is operated stoichiometrically, which enables the use of a cost-efficient three-way catalytic converter. By vehicle emulation of a non-hybrid vehicle on the Worldwide harmonized Light vehicles Test Procedure (WLTP), we demonstrate that transient operation of the natural gas-Diesel engine is also possible, thus enabling a non-hybridized powertrain as well.

Hybrid-Electric Vehicle with Natural Gas-Diesel Engine

In this paper we demonstrate the potential of combining electric hybridization with a dual-fuel natural gas-Diesel engine. We show that carbon dioxide emissions can be reduced to 43 gram per kilometer with a subcompact car on the New European Driving Cycle (NEDC). The vehicle is operated in charge-sustaining mode, which means that all energy is provided by the fuel. The result is obtained by hardware-in-the-loop experiments where the engine is operated on a test bench while the rest of the powertrain as well as the vehicle are simulated. By static engine measurements we demonstrate that the natural gas-Diesel engine reaches efficiencies of up to 39.5%. The engine is operated lean at low loads with low engine out nitrogen oxide emissions such that no nitrogen oxide aftertreatment is necessary. At medium to high loads the engine is operated stoichiometrically, which enables the use of a cost-efficient three-way catalytic converter. By vehicle emulation of a non-hybrid vehicle on the Worldwide harmonized Light vehicles Test Procedure (WLTP), we demonstrate that transient operation of the natural gas-Diesel engine is also possible, thus enabling a non-hybridized powertrain as well.