Testing procedures and Test cycles for measuring fuel consumption

Commercial vehicles (trucks and buses) are typically classified by attributes Gross Vehicle Weight (GVW) and footprint. Introducing Attribute-based target fuel consumption standards for trucks and buses is a complex task because fuel consumption of trucks and buses depends on many factors apart from the sheer vehicle weight or footprint, such as average transported payload, road gradients, drag and rolling resistance from vehicle, engine characteristics, gear ratios and type of transmission, and auxiliary power demand. Further, fuel savings and the impacts of technologies on fuel consumption are highly dependent on whether these vehicles are mainly used for urban driving (such as delivery trucks or intra-city buses) or long-haul (mainly highway) shipments or inter-city buses. Urban and regional delivery and transportation services are dominated by small and medium freight trucks and buses, typically up to a gross vehicle weight of 16t; long-haul trucking and inter-city transportation are mostly carried out with large trucks and buses up to a gross vehicle weight of 40t. Urban and regional delivery is characterised by lower average speeds, frequent acceleration and deceleration, and

frequent stops. Long-haul services are mostly carried out at high and fairly constant speeds, so improving aerodynamics and reducing rolling resistance are key measures.

In order to define reasonable and meaningful fuel consumption standards, all these factors need to be taken into account for each segment of vehicles. Therefore, standard driving test cycles are required to test the vehicles for fuel consumption and pollutant emissions incorporating many, if not all, of these factors for various categories of vehicles.

The basic input for comparison of fuel economy and development of fuel consumption standards is fuel economy data of various models of vehicles. In order to compare fuel economy of different vehicles in a consistent and unbiased manner, a systematic approach must be used. The fuel economy and pollution emissions15 estimates are usually measured in a “homologation” laboratory under predefined test conditions for a range of standardised driving cycles or test cycles to simulate typical driving conditions. There are numerous possible configurations of trucks and buses; homologating each vehicle configuration is not realistic. Further, the layout of a vehicle in the testing laboratory requires substantial investment. Therefore, several other methods are used to test vehicles for fuel efficiency and pollutant emissions. In order to measure fuel economy, typically four different approaches are considered:

(1) Vehicle testing using chassis dynamometer in a homologation laboratory

(2) Engine testing using engine or bench dynamometer in a homologation laboratory - Given the size and weight of trucks and buses, often only the engine is tested on a bench dynamometer to measure fuel economy and pollutant emissions.

(3) Computer Simulation - Computer simulation of the whole truck (typically in combination with engine testing on a bench dynamometer) is a favoured option by industry. The Greenhouse Gas Emissions Model (GEM) simulation tool developed in the US adopts this strategy, complementing the vehicle modelling tool with engine dynamometer tests.

(4) On-road testing of vehicles

15 _{Such as carbon dioxide (CO}

2), carbon monoxide (CO), hydrocarbons (HC), particulate matters (PM) and

Table 4.4: Testing options for measurement of vehicle fuel economy

S No Type of test Parts simulated Cost of test Countries considering fuel consumption norms for HDVs

(1) On-road None Low None

(2) Computer

simulation All Low US, EU, Japan, China

(3) Engine dynamometer

Road and non-

engine components High US, EU, Japan (4) Chassis

dynamometer Road Very High China

The unit for measuring fuel consumption need not only be Litre per kilometre. For vehicle standards, Litre per tonne-kilometre can also be used to measure fuel consumption for trucks and buses. For engine standards, Litre per kWh can also be used to measure fuel consumption for trucks and buses. Further, fuel economy standards can also be developed instead of fuel consumption standards with units as inverse of fuel consumption units (like kmpl, tonne-km per litre, etc.).

The fuel economy of the entire fleet of vehicles, in actual on-road conditions, depends on many factors and is difficult to measure. The difference between tested and in-use fuel economy is due to attributes of the vehicle, the driver and the road. In India, vehicles’ average age and road conditions are the main factors that keep average fuel economy lower. However, vehicle average size and embedded technologies also play an important role for the average on-road fuel economy. Isolating the exact impact of each factor is difficult because of limited data, therefore, the tested fuel economy of new vehicles based on various methods above is a good indicator of their performance in-use, but is likely to underestimate fuel consumption.

The fuel economy details of various vehicle models of trucks and buses are neither disclosed by the manufacturers nor collected by testing agencies like ARAI. ARAI, however, collects data for engine testing of trucks and buses models using engine or bench dynamometer. Therefore, setting up fuel consumption vehicle standards will require testing of various available models of buses and trucks prior to setting up the standards. Moreover, test cycles will have to be standardised for various categories for which standards are to be developed. On the other hand, engine test data (in Litre / kWh) could be used to setup engine standards for fuel consumption in the first phase, followed by vehicle standards for fuel consumption in subsequent phases.