Real Driving Emission Calibration—Review of Current Validation Methods against the Background of Future Emission Legislation

Abstract

Reducing air pollution caused by emissions from road traffic, especially in urban areas, is an important goal of legislators and the automotive industry. The introduction of so-called “Real Driving Emission” (RDE) tests for the homologation of vehicles with internal combustion engines according to the EU6d legislation was a fundamental milestone for vehicle and powertrain development. Due to the introduction of non-reproducible on-road emission tests with “Portable Emission Measurement Systems” (PEMS) in addition to the standardized emission tests on chassis dynamometers, emission aftertreatment development and validation has become significantly more complex. For explicit proof of compliance with the emission and fuel consumption regulations, the legislators continue to require the “Worldwide Harmonized Light Duty Vehicle Test Cycle” (WLTC) on a chassis dynamometer. For calibration purposes, also various RDE profiles are conducted on the chassis dynamometer. However, the combination of precisely defined driving profiles on the chassis dynamometer and the dynamics-limiting boundary conditions in PEMS tests on the road still lead to discrepancies between the certified test results and the real vehicle behavior. The expected future emissions standards to replace EU6d will therefore force even more realistic RDE tests. This is to be achieved by significantly extending the permissible RDE test boundary conditions, such as giving more weight to the urban section of an RDE test. In addition, the introduction of limit values for previously unregulated pollutants such as nitrogen dioxide (NO2), nitrous oxide (N2O), ammonia (NH3) and formaldehyde (CH2O) is being considered. Furthermore, the particle number (for diameters of solid particles > 10 nm: PN10), the methane (CH4) emissions and emissions of non-methane organic gases (NMOG) shall be limited and must be tested. To simplify the test procedure in the long term, the abandonment of predefined chassis dyno emission tests to determine the pollutant emission behavior is under discussion. Against this background, current testing, validation, and development methods are reviewed in this paper. New challenges and necessary adaptations of current approaches are discussed and presented to illustrate the need to consider future regulatory requirements in today’s approaches. Conclusions are drawn and suggestions for a robust RDE validation procedure are formulated.

Concepts for Hydrogen Internal Combustion Engines and Their Implications on the Exhaust Gas Aftertreatment System

“…Pollutant emissions are mainly nitrogen-based, with nitrogen oxide (NO X ) as the main raw emission. Potential secondary emissions produced in the exhaust aftertreatment system (EATS) are ammonia (NH 3 ) and nitrous oxide (N 2 O), which, with the introduction of the EU7 legislation, are also expected to receive limit values that must be met in the real driving emissions type approval tests on the road [23][24][25]. Carbon-based pollutant emissions (carbon monoxide and hydrocarbons) can only result from lubrication oil consumption and are expected to be on a very low level.…”

Exhaust Emissions Measurement of a Vehicle with Retrofitted LPG System

“…The exact scope of the planned adjustments in the transition from Euro 6 to Euro 7 is not yet known in detail. However, it is already clear that in addition to improved exhaust after-treatment systems and advanced measurement systems for the accurate measurement of very low concentrations of already limited and other new pollutants, extended or even new development structures and procedures need to be provided in some areas [37,38].…”

Real Driving Emissions—Conception of a Data-Driven Calibration Methodology for Hybrid Powertrains Combining Statistical Analysis and Virtual Calibration Platforms

“…Requirements for the distance shares for urban, rural, motorway as well as the geodetic profile of the traveled road with respect to the positive cumulated elevation gain as well as the absolute difference between the start and end of the trip define the general conditions of the route [4]. Looking forward to planned adjustments by the EU7 standard, potential restrictions and ranges for these limitations can be omitted or extended [16][17][18][19].…”

“…In addition, increasing vehicle variants with different powertrain modifications lead to an exponential growth of test cases to be considered [33]. As demonstrated on the right chart in Figure 1, this puts challenges onto the available test resources [16]. The introduction of new test facilities is required to keep up with the exponential growth in tests to be carried out.…”