Gerrit Kadijk BSc
- emission factors
TNO has been commissioned by the Ministry of Infrastructure and the Environment to conduct an in-service testing programme for cars and vans. In the context of this multi-annual programme, TNO subjects vehicles that are in everyday use to a range of measurement programmes. In addition, their emissions and fuel consumption are measured in accordance with the official testing procedure for type-approval testing and under real-world conditions.
These measurements have two principal objectives. Firstly, the aim is to obtain an understanding of the real-world emission performance of vehicles and specific technologies. Based on an average picture of real-world emissions, national road vehicle emission factors are established each year. In the Netherlands, these emission factors are used to calculate air quality, to determine total emissions, and to calculate the effectiveness of individual measures. The programme also delivers objective information and insights that the Dutch government can integrate into EU policy processes, for the purpose of improving emissions legislation and the corresponding testing procedures.
TNO measures vehicle exhaust gas emissions, both on a dynamometer in the laboratory and on the road using mobile emission measuring equipment, while driving in normal traffic conditions. Each year, in consultation with the Ministry, TNO selects several types of cars for testing.
Measurements in the lab are carried out on a dynamometer, where emissions are measured using the most modern emission measurement equipment as required by the type approval test procedures. The test conditions in the laboratory are very well controlled and reproducible so that measurements on different vehicles and in different labs are comparable with each other.
On a chassis dynamometer, which simulates the mass and the rolling and air resistance of the vehicle, driving cycles are run. However, besides the prescribed type approval test procedures for the NEDC route cycle (New European Driving Cycle), TNO also uses other driving cycles which better represent the various conditions of use of vehicles in practice than the NEDC cycle.
However, the widely varying conditions encountered on the public road can not all be simulated on a dynamometer. It has been found that, under real-life conditions, modern vehicles’ emissions are highly sensitive to these conditions. Thus, the determination of real-world emissions requires on-road measurements, using specialised mobile measuring equipment.
Using a Portable Emissions Measurement System (PEMS), TNO can accurately measure a vehicle’s real-world CO, CO2, HC and NOx emissions while it is being driven on the public road. PEMS is a complex system that can only be installed and operated by qualified personnel. During test drives, a TNO driver follows a given route in normal traffic while a measurement technician operates the equipment. To ensure that the measurements are fully comparable, a standard route has been developed that includes representative sections of urban roads, country roads and motorways.
In Brussels, a procedure is being prepared for measuring the Real Driving Emissions (RDE) of Euro VI cars and vans, using PEMS. RDE legislation is scheduled to come into force in 2017.
The compact Smart Emissions Measurement System (SEMS) can measure a vehicle’s NOx and CO2 emissions on the road. The system is easily installed and removed, and the owners can make normal use of their vehicle while measurements are being made. This makes it possible to collect and analyse large amounts of measurement data during extended periods (e.g. one month) of normal use.
TNO developed SEMS in 2014 to enable a vehicles’ NOx emissions to be rapidly and cheaply screened in real-life situations. SEMS is not a regulated measuring instrument, and it is less accurate than PEMS. In some cases, SEMS measurements can trigger a follow-up measurement using PEMS.
For Euro 5 and subsequent classes, on-road measurements with PEMS and SEMS will increasingly be the basis for determining emission factors for cars and vans. The real-world NOx emissions of Euro 5 and Euro 6 diesel vehicles have been the focus of a major research effort in recent years. On average, these emissions are a factor of 3 to 10 times higher than the values measured in the type-approval test.
These studies are unrelated to enforcement, i.e. determining whether specific vehicle models do or do not meet the emission standards. Nor are the test methods used suitable for detecting fraudulent practices relating to cars. A detailed investigation into the causes of the high real-world emissions that have been identified would require a different type of investigation than the emission measurements TNO made for the Ministry of Infrastructure and the Environment.
You can find the latest reports on emission measurements on cars and vans below.