Diesel series hybrid vehicles show best well-to-wheel efficiency

A well-to-wheel (WTW) analysis assesses the total fuel cycle of a vehicle from crude oil extraction right through to general daily operation. Such research helps in understanding the real impacts on the environment and defining future strategies for government and Industry.

Speaking during F+L Week 2022 in Bangkok, Thailand, on April 28, R. V. Ravikrishna, Pratt & Whitney Chair Professor at the Indian Institute of Science, Bangalore, presented the first comprehensive study of WTW analysis of auto fuels in the Indian Context. The research considers both energy use and emissions in each stage of fuel production and use.

The study analysed five fuel pathways and 12 fuel and vehicle technology combinations including conventional, series hybrid and plug-in hybrid configurations for gasoline, diesel and CNG. Hybrid hydrogen fuel cells along with their plug-in version and battery electric vehicles were also considered.

Ravikrishna concluded that the diesel series hybrid shows maximum WTW efficiency amongst all drivetrains, primarily due to the inherent higher engine efficiency. Hybridisation tends to significantly improve WTW efficiency and reduce WTW carbon dioxide (CO₂) emissions, says Ravikrishna.

Overall, hybrids demonstrated higher WTW efficiency as compared to plug-in hybrids and battery electric vehicles – due to the lower well-to-tank (WTT) efficiency associated with the production of electricity. The existing electricity generation mix (2019-2020) in India, with around 70% dependence on inefficient coal power plants, makes the electricity pathway less efficient and high CO₂ emitting.

Hybrid CNG vehicles exhibited the lowest WTW CO₂ emissions, mainly because of the relatively lower CO₂ emissions associated with both the WTT and tank-to-wheel (TTW) phases, says Ravikrishna. Hydrogen fuel cell vehicles have lower WTW efficiency as compared to conventional fuels because of the lower efficiency associated with the hydrogen production pathway (from natural gas).

Ravikrishna noted that with a greater generation of electricity from renewable and efficient energy sources, the potential for improvements in the WTW efficiency for battery electric vehicles and plug-in hybrids is very high. The Indian Institute of Science professor called for an aggressive shift to renewables in India by 2030. He also noted that even with India’s current energy mix, battery-electric two-wheelers do offer higher WTW efficiency than the conventional gasoline-powered vehicle, making a strong case for their electrification.

The study was commissioned by the Indian government and Ravikrishna acknowledged the involvement of the Office of the Principal Scientific Advisor to the Government of India, Toyota Kirloskar Pvt. Ltd., TVS Motors Pvt. Ltd., ONGC, IOCL, BPCL, HPCL, GAIL, OIL, Ministry of Railways, Ministry of Coal, Ministry of Petroleum & Natural gas (PPAC – Petroleum Planning & Analysis Cell) and Mr. Yash Nandola, Mr. Uttam Krishna, Dr. M. Himadindu, Dr. B. Prasad, and Dr. Santanu Pramanik.