**6. Validation of the Conventional Vehicle Model**

In the R&D project mentioned in the introduction, several road tests were conducted in the GOST driving cycles involving vehicles equipped with the developed diesel and gas engines. Furthermore, by way of comparison, a vehicle equipped with a production gas-fueled engine was tested in the same driving conditions. The logged parameters were the vehicle velocity, engine rpm, and fuel consumption. The logs allowed for simulating the tests and validating the model of the conventional vehicle.

The baseline vehicle was an articulated road train (tractor-trailer) intended for long haulage. It was equipped with a manual 16-speed mechanical gearbox with two ranges, the high and low, with eight gears each. In normal driving conditions, the former is usually preferred over the latter. The test mass of the vehicle was 44,000 kg (equals to the tractor-trailer gross mass).

Prior to the driving cycle tests, coast-down experiments were performed to estimate the rolling and air resistance forces. Analysis of the coast-down results and the vehicle's technical specification available from the manufacturer allowed for identifying the parameters of the model of vehicle dynamics (Equation (1)), which are specified in Table 6.


**Table 6.** Parameters of the model of vehicle dynamics.

Table 7 shows the fuel economy data obtained using the field experiments and simulations, as well as the simulation errors, for the vehicles equipped with the three mentioned engines.

**Table 7.** Comparison between the experimental and calculated fuel economy for the vehicles equipped with the conventional powertrains.


The higher error for the production gas engine in the city cycle resulted from the unknown experimental velocity data, which compelled to use the velocity log from another vehicle's test. Despite the same driving schedule, the velocity profiles most likely had certain differences since the accuracy of road-performed cycles strongly depends on the driver's behavior, which obviously cannot be repeated precisely from test to test.

In general, the model was considered to have sufficient accuracy for performing further simulations with the hybrid vehicles.
