Maruti Suzuki’s compelling fuel efficiency pitch — 1,200 km on a single tank! — for the hybrid version of its new Grand Vitara premium SUV rides on the underrated petrol engines that leverage a range of mild and strong hybrid options, marking a significant departure from the biggest trick that carmakers have employed for the better part of the last two decades: the diesel mill.

India’s largest carmaker is not alone — a slew of tweaks and innovations that stretch every litre of fuel are bringing back petrol variants as the top models across manufacturers.

Because they use compressed air with no spark plug for the ignition process, diesel engines use 15%-20% per cent less fuel compared to a petrol engine vehicle, which translates into lower operating costs in addition to providing higher low-end torque (the turning force). This made diesel the primary choice for utility vehicles. However, diesel engines entailed higher upfront costs, and their servicing and maintenance costs tended to be more.

While diesel continues to be a pricier, hot option among the variants on offer, it is no longer the mainstay mileage buster for a number of carmakers, including Maruti Suzuki. The return to petrol has been triggered by the stricter BS6 emission norms rolled out two years ago and, more importantly, a range of tech alterations to deliver the most bang for the customer’s buck.

TWO FUEL INJECTORS PER CYLINDER: In Maruti Suzuki’s new DualJet technology, two injectors are placed close to the engine inlet valves, which enables finer atomisation of fuel, resulting in more complete combustion. The dual jets also help deliver smoother and faster responses at low throttle inputs, a regular feature in city driving conditions.

This leads to cooler running, which allows manufacturers to use a higher compression ratio, which, in turn, helps convert the energy in the fuel to mechanical energy much more efficiently. The combustion chamber used in these engines is more compact, which makes the fuel and air mix better before it is ignited, thereby delivering better efficiency.

The result is really high mileage of 22-26 kpl under Automotive Research Association of India (ARAI) test conditions. Maruti Suzuki has three new DualJet engines as part of its K-series C engine updates that now power the new Celerio, the Baleno, the Swift, the updated Brezza, and the S-Cross that was sold earlier.

DualJet, along with Maruti Suzuki’s latest Heartect platform, has ensured that eight of its vehicles are in the 10 top mileage petrol cars, according to a list compiled by Autocar India based on official figures revealed by manufacturers and/ or certified by ARAI.

Models: Suzuki Brezza, Baleno, Celerio

GASOLINE DIRECT INJECTION: GDI is a sophisticated engine that injects fuel precisely and at very high pressure directly into the combustion chamber of the engine. This leads to higher fuel efficiency, higher power output, and significantly lower emissions by overcoming the problem of a compromised combustion ratio when fuel and air are mixed in the intake chamber, as in most traditional vehicles. Hyundai has a range of GDI turbocharged engines. Models: Hyundai Creta, Verna, Venue

TURBO PETROL ENGINES: Korean and German carmakers are counting on “engine downsizing” in the petrol variants, with a turbocharged engine. These are essentially smaller engines, with typically fewer cylinders, which are generally more fuel efficient but low on rated power. This power deficiency is overcome by using a turbocharger — a turbine that is powered by the engine’s exhaust fuel to subsequently power that additional compressed air into the combustion chamber, resulting in extra combustion of the air-fuel mix. The result: these smaller turbocharged engines produce more energy than a bigger engine, while guzzling less petrol.

The technology is relatively old — Ford Ecosport’s EcoBoost engine was an early mover, followed by the Volkswagen Polo. But both these cars had low mileage. With the BS6 norms kicking in, Hyundai, Skoda, Mahindra & Mahindra, and Tata Motors have all deployed smaller, turbocharged petrol engines of the kind used in the Hyundai Venue and VW Taigun. In all these cases, the internal combustion engine has lower cubic capacity, but not at the expense of power. Maruti Suzuki is an exception, relying entirely on regular, naturally aspirated (non-turbo) petrol engines with its DualJet tweak.

Models: Hyundai Venue, VW Taigun, Skoda Slavia

MILD HYBRID TECH: Maruti Suzuki has deployed mild hybrid — or what it calls “Smart Hybrid” — technology across its higher-end sedan and utility vehicle models to increase fuel efficiency. The engine automatically stops when idle, and starts silently when optimal conditions are met in manual and automatic transmissions. It comes with a dual battery setup including a Lithium-ion battery, which stores the energy generated during braking to assist the engine’s idle start-stop and torque assist functions. The energy stored in the Lithium-ion battery assists during acceleration.

STRONG HYBRID TECH: The strongest Japanese counter to the diesel engine, led by the Maruti Suzuki India and Toyota Motor combine, and Honda Motor, is focussed on petrol-powered engines mated with hybrid systems. Two new Suzuki-Toyota SUVs, the Grand Vitara and the Toyota Hyryder, are powered by petrol engines with hybrid setups.

A hybrid system sometimes includes a petrol engine that’s paired with an electrical motor and a Lithium-ion or Nickel-metal Hydride (NiMH) battery pack that allows the automobile to be pushed in purely electrical mode for short distances. The battery pack is recharged by the engine, or by way of regenerative braking. Maruti Suzuki and Toyota claim that their strong-hybrid SUVs return a fuel efficiency of 27.97 kpl, a claim that is, however, still to be certified by ARAI. If the ARAI figure does match the manufacturers’, the Grand Vitara and Hyryder would be the most fuel-efficient SUVs in their segment, and among the top mileage cars in the country. Honda too claims that its City hybrid will return an average fuel efficiency of 26.5 kpl.

Models: Honda City e:HEV, Toyota Urban Cruiser Hyryder, Suzuki Grand Vitara

Additional gears allow the engine to operate at efficient speeds more often. In the case of its automatics, Maruti Suzuki has shifted from its 4-speed torque converter to a new 6-speed gear configuration.

Continuously Variable Transmission (CVT) automatics have an infinite number of “gears”, providing seamless acceleration and improved fuel economy. Dual-clutch transmissions (DCT), which have two clutches for seamless automated shifting, suffer less energy loss than traditional automatics.

Models: Suzuki XL6 (6-speed torque convertor), Hyundai Venue (DCT), Hyundai i20, Toyota Glanza, Suzuki Baleno (CVT gears)

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Anil SasiAnil Sasi is National Business Editor with the Indian Express and writ... read more