EMISSION TEST CYCLES

The US and European driving cycles used for emission measurement are presented below. Most of the other countries follow either the European or the US test methods except Japan which has its own driving cycles. In India European test methods are used except for the motorcycles and three wheelers.

Driving Cycles for Light Duty Vehicles

The emission test driving cycles are composed of a cold start period, idling, moderate acceleration and deceleration, and cruise modes.  The test cycle is given in terms of vehicle speed versus time. The light and medium duty vehicles are driven through the prescribed driving cycle on a chassis roller dynamometer. During operation the engine is required to develop road horse power that depends on the vehicle speed fopr a given vehicle.  The road horsepower requirement versus speed data as provided by the vehicle manufacturer or determined by vehicle coast down test is stored into chassis dynamometer controller to simulate the real life road operation of the vehicle. The vehicle weight i.e. inertia needed during transient modes of the driving cycle is simulated by mechanically changing the rotating masses or electronically changing the inertia on the roller dynamometer. A typical emission test facility with a vehicle operating on chassis dynamometer is shown in Fig 4.1

European Test Driving Cycle

The driving cycles followed in Europe for light and medium duty vehicles is shown in Fig. 4.2. The European test cycle is composed of steady operation modes derived from the actual vehicle operation data on road. Although it consists of acceleration and deceleration modes but as all the modes represent averaged operating conditions, the cycle is often referred to as steady mode cycle.  The European test cycle as given in Fig. 4.2 was implemented from Euro 1 emission standards in 1992. It has two parts;

(i) an urban driving cycle (ECE 15) and

(ii) an extra-urban driving cycle (EUDC)

The break-up of different operating modes in the two parts of the cycle is also given in Figure 4.2.

Prior to Euro 1 regulations, only the ECE 15 cycle was used. The low speed urban test cycle consists of repetition of 15 mode cycle four times without interruption for a total duration of 780 seconds.  The total distance covered is 4.052 km at an average speed of 19 km/h. The high-speed test cycle called as Extra Urban Driving Cycle (EUDC) is carried out after the ECE-15 cycle. This high-speed cycle has maximum speed of 120 km/h. The EUDC part gives a higher contribution to NOx while the ECE-15 cycle has more contribution to CO and HC emissions.
Emission measurement commences with the engine cold start at the beginning of the first ECE-15 mode cycle itself. The emissions are measured using CVS technique as explained later.