What makes some cars so fuel efficient?

While some hybrid cars return above 25 km/litre, even conventional petrol cars have become quite fuel efficient

auto sector. auto industry
CNG cars can be even more fuel efficient; for example, the Alto CNG returns 31.59 km/kg on CNG. (IE)

Last week, Honda launched the new City midsize sedan, whose hybrid variant (called the City e:HEV) returns a claimed fuel efficiency of 27.13 km/litre on petrol.

Also called hybrid electric vehicles (HEVs), there are now six HEVs in India, including Maruti Suzuki Grand Vitara (27.97 km/litre), Toyota Urban Cruiser Hyryder (27.97 km/litre), Toyota Camry (23.27 km/litre), Toyota Innova HyCross (21.1 km/litre) and Toyota Vellfire (16.3 km/litre).

Why are HEVs so fuel efficient?

HEVs use two sources of power—internal combustion engine (usually petrol) and electric motor. When you start driving slowly, HEVs run only on electric power. If you floor the accelerator, both the engine and the electric motor power the wheels. As you approach a traffic signal and apply brakes, the regenerative braking turns the car’s kinetic energy into electric energy and charges the battery. On a complete stop, the petrol engine shuts down and the electric motor powers the AC, without the unnecessary fuel consumption and emissions associated with idling.

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But this complicated set-up makes HEVs more expensive than conventional petrol cars. For example, the City petrol is priced from Rs 11.49 lakh to Rs 15.97 lakh (ex-showroom), but the City e:HEV is priced from Rs 18.89 lakh to Rs 20.39 lakh. Similarly, the Grand Vitara petrol costs Rs 10.45 lakh to Rs 16.89 lakh, but the hybrid variants cost Rs 17.99 lakh to Rs 19.49 lakh.

Other fuel-efficient cars

You don’t always need an electric motor to bump up the fuel efficiency of a car. Using light-weighting technologies and other innovations can also make cars more fuel efficient.

Maruti Suzuki Celerio, for example, is India’s most fuel-efficient non-hybrid car, with a claimed figure of 26.68 km/litre. CV Raman, chief technical officer, Maruti Suzuki India, recently told FE that five engineering changes bumped up the fuel efficiency of the Celerio.

1. The Suzuki HEARTECT platform reduced weight.

2. The idle start-stop technology (the engine automatically switches off when the car comes to a complete stop and switches on when you press the clutch).

3. Maruti Suzuki reduced friction losses by using lower viscosity engine oil.

4. The aerodynamic body of the car.

5. The Celerio rides on lower rolling-resistance tyres.

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“These five changes, in combination, led to 16-23% better fuel efficiency in the Celerio,” Raman said.

Maruti Suzuki applied the same changes to the XL6, a big car, to make it almost as fuel efficient as some HEVs; the XL6 returns a fuel efficiency of 20.97 km/litre.

Other cars with fuel efficiency above 20 km/litre include the following:

—Maruti Suzuki Alto AGS (24.9 km/litre).

—Maruti Suzuki Wagon R AGS (24.43 km/litre)

Maruti Suzuki Baleno and Toyota Glanza (22.94 km/litre).

—Maruti Suzuki Dzire AGS (22.61 km/litre).

Renault Kwid (22.3 km/litre).

CNG cars can be even more fuel efficient; for example, the Alto CNG returns 31.59 km/kg on CNG. “The calorific value of CNG is more than that of petrol, and that’s why km/kg of a CNG car is usually better than km/litre of a similar-engine petrol car,” Raman said.

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First published on: 08-03-2023 at 15:05 IST
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