Time-speed data points

The FTP (Federal Test Procedure) heavy-duty transient cycle is used for regulatory emission testing of heavy-duty on-road engines in the United States [40 CFR 86.1333]. The FTP transient test is based on the UDDS chassis dynamometer driving cycle. The cycle includes “motoring” segments and, therefore, requires a DC or AC electric dynamometer capable of both absorbing and supplying power.

The transient test was developed to take into account a variety of heavy-duty truck and bus driving patterns in American cities, including traffic in and around the cities on roads and expressways. The FTP cycle consists of four phases, including (1) New York Non Freeway (NYNF) phase typical of light urban traffic with frequent stops and starts, (2) Los Angeles Non Freeway (LANF) phase typical of crowded urban traffic with few stops, (3) Los Angeles Freeway (LAFY) phase simulating crowded expressway traffic in Los Angeles, followed by (4) a repetition of the first NYNF phase. The variation of normalized speed and torque with time is shown in Figure 1.

FTP Transient

Figure 1. FTP Transient Cycle

The cycle is run as both a cold- and a hot-start test. Typically, the engine is soaked overnight and a cold-start test is performed in the morning. The cold-start test is followed by a 20-minute soak period and a minimum of three consecutive hot-start tests, with a 20-minute soak period between each hot-start test. The composite, brake-specific FTP results are obtained by dividing the weighed emissions and fuel consumption (in grams) by the weighed mechanical work (in bhp-hr), using a weighing factor of 1/7 and 6/7 for the cold- and hot-start results, respectively [40 CFR 86.1342-90].

The average load factor of the FTP cycle is roughly 20-25% of the maximum engine power available at a given engine speed. The equivalent average vehicle speed is about 30 km/h and the equivalent distance traveled is 10.3 km for a running time of 1200 s. Heavy duty diesel engines tested on the FTP cycle produce medium to high exhaust gas temperatures. Generally, the temperature is at a medium level between 250 and 350°C, but there are hot sections with temperatures reaching as high as 450°C.