A Comparative Analysis of Passenger Car Fuel Economy between Laboratory and Real Driving Testing

In India, fuel economy is one of the most critical factors influencing a customer's decision to own a passenger car. Beyond consumer preference, fuel consumption also plays a significant role in the nation's energy security. In line with this, the government promotes fuel-efficient vehicles and technologies through various regulations, policies, and mandates. Vehicle manufacturers, in response, focus on designing vehicles that align with both customer expectations and regulatory requirements. Fuel economy certification is typically based on standardized laboratory tests that simulate controlled environmental conditions, driving cycle (MIDC), vehicle load, and operation of electrical and electronic systems. However, actual on-road driving conditions by end user vary significantly due to factors such as traffic conditions, ambient temperature, air conditioning use, driving behavior and variable loading of the vehicle. With implementation of Bharat Stage VI, Real Driving Emission (RDE) became mandatory from April 2023 to meet the requirements of conformity factors (CF) for NOX and PN emission. RDE regulation scope doesn’t include measurement or compliance for fuel economy during real driving condition. For the purpose of this study, laboratory and real driving emissions (RDE) testing were carried out in accordance with AIS 137 Part 3. For systematic comparison, fuel economy was calculated after modifying Carbon Balance equation in line to CAFÉ regulation S.O. 1072 (E) Dated 23rd April 2015. This study presents a comparative analysis of fuel economy results obtained from the testing different vehicles operating on different fuels like Gasoline, Diesel and Bi-fuel (Compressed Natural Gas (CNG) + Gasoline). The paper concludes with finding of study as impact of real-world driving conditions, particularly of ambient temperature and real driving on fuel efficiency of passenger cars.