Green NCAP performs a wide range of tests on cars in the laboratory. This is the best way of ensuring controlled conditions, to ensure that all cars are tested in the same way so that their results are comparable.
In laboratory tests, a car is put on a chassis dynamometer – a ‘rolling road’ – and is driven through a prescribed test cycle. During the test, exhaust gases are collected. These gases are analysed at the end of the drive-cycle to determine the amount of pollutant emissions, particulate matter and greenhouse gases the car emitted during the cycle.
The dynamometer can be set to simulate the resistance a car would normally experience in real-world driving. These are mainly an inertial resistance (i.e. a heavier car is more difficult to accelerate than a light one) and aerodynamic drag. So, a light, streamlined car is tested on the dynamometer with less resistance than a heavy one with poor aerodynamics.
At the core of Green NCAP’s lab tests is the World-harmonised Light-vehicles Test Cycle (WLTC), introduced in 2017 as a global test procedure, developed on the basis of global real-driving data and representative of everyday driving. The WLTC replaced the old NEDC test cycle (New European Driving Cycle) which had been in use for some 40 years previously. The WLTC driving cycle is divided into four parts (low, medium, high, extra high), which address different types of use, with a wide variation of driving behaviour and driving situations. Each part represents different driving phases like city or urban driving with a variation of vehicle speeds and different stop times, accelerations and braking phases.
Green NCAP’s laboratory tests are based on the WLTC test procedure but with more realistic boundary conditions. All tests (except the Cold Ambient Test / CAT at -7°C) are performed with an ambient temperature of about 14°C which is much closer to the European average than the one used (23°C) in the legislative test cycle. In addition, the conditioning of the car corresponds more to the real world: the test is driven with a realistic payload and with activation of typical vehicle systems like headlights and air-conditioning.
Green NCAP also evaluates the robustness of the vehicle’s exhaust after-treatment system. This ‘robustness’ checks that the emissions-control systems work effectively over a broad range of conditions and not just in one prescribed test. To evaluate this, the tests are performed with different ambient temperatures and starting conditions like cold or warm engine start.
The main purpose is to have realistic and comparable results from different cars and propulsion systems.
To evaluate the robustness of the exhaust after-treatment system at high engine loads, a motorway test-cycle (BAB130) is also performed. This test cycle has a maximum speed of 130 km/h and includes several hard accelerations from 80 km/h to 130 km/h.
In summary four different lab tests are rated:
Plug-in hybrid electric vehicles (PHEVs) are subjected to all of these laboratory tests in charge-sustaining mode (i.e. when running mainly using the combustion engine). In charge-depleting mode (i.e. when being run primarily on battery power), only the WLTC cold test is used.
During all cycles, the pollutants (HC, CO, NOx, PN, PM) and CO2 emissions are measured as well as fuel consumption values.
For more detailed information, see Test Procedures.
The tests leave no room for engine management strategies that are not reflective of real-world driving.
The main purpose of the lab tests is to have the most realistic and comparable results from different cars and propulsion systems in terms of their emissions and fuel economy/energy efficiency. The test conditions, the vehicle set-up and the execution of the tests are standardised and clearly defined. This is important for a fair and a high-quality assessment and evaluation of cars. Between them, the tests cover such a broad range of engine performance that there is little opportunity for manufacturers to employ engine management strategies that are not reflective of real-world driving. Only lab tests with a standardised and repeatable methodology allow consumers to compare different car models.