Are Plug In Hybrid Cars Really Efficient Or Just Overhyped

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Will the Malaysian government support this technology?
One of our Malaysia Car of the Year judges was singularly intrigued by the new generation of Plug-in Hybrid Vehicles (PHEV) and their stated 1,000+km driving range.
This judge has probably clocked more miles test driving some of this year’s nominees in the PHEV category than the remaining 10 judges put together.
He tells us he learned an important lesson driving one of Malaysia’s top selling PHEVs models — never run a PHEV down to zero battery charge and zero petrol.
This is because the car is designed to shut down completely and protect itself. You won’t be able to restart it with a jumper cable or a jerry can of petrol. Instead you will have to transport it on a car carrier to a designated service centre or have it reset by a professional PHEV technician.
So, always make sure that your PHEV never runs out of petrol.
He also learned that fuel consumption increases significantly when the traction battery is depleted and the car runs solely on its petrol engine.
Our intrepid judge learned this the hard way when, determined to prove a point, he poured in just two litres of petrol — confident it would suffice for a 12km drive to Hospital Kuala Lumpur. Well, the PHEV became a fuel guzzler because it also had to charge the traction battery.
Take it from me — running out of petrol in a PHEV is way more serious than in a normal car.
So, are today’s plug-in hybrid cars as fuel efficient as claimed, or is that just marketing hype?
The short answer is, yes. A 45% thermal efficiency for a hybrid-dedicated engine is not only possible but is now the benchmark for leading manufacturers in China and globally. This is a real achievement and not mere marketing hype.
Let’s break down why this is possible and the role of technologies like the high-efficiency turbocharger.
The foundation: what is thermal efficiency?
Thermal efficiency refers to the proportion of fuel energy that is converted into mechanical work to propel a vehicle, rather than dissipated as heat.
For most of automotive history, standard gasoline engines have operated at around 30-35% thermal efficiency.
The rest of the energy is wasted primarily through heat in the exhaust gases, heat rejected to the cooling system, as well as friction and pumping losses within the engine.
Achieving 45% thermal efficiency means the engine is significantly better at capturing energy from fuel.
This achievement is the result of several technologies working in harmony. A high-efficiency turbocharger is a critical enabler, but it is just one part of the puzzle.
While premium brands have their own PHEV technology, it is the Chinese car makers that have mastered this technology to an affordable price point for mainstream car buyers.
While premium brands have their own PHEV systems, it is the Chinese automakers that have successfully brought the technology to a price point that makes it accessible to mainstream buyers. Let’s look at what that technology involves.
Atkinson/Miller cycle: This is fundamental for hybrids as was proven 25 years ago when Toyota launched its Prius, a mild hybrid. Unlike a standard Otto cycle engine, the Atkinson cycle keeps the intake valve open longer during the compression stroke. This effectively creates a longer “power” stroke than “compression” stroke, extracting more work from the burning fuel. It sacrifices some peak power for much higher efficiency — a perfect trade-off for a hybrid where the electric motor provides the missing power for acceleration.High compression ratio: These engines run very high compression ratios — often 13:1 to 16:1. Squeezing the air-fuel mixture more before ignition makes the combustion more powerful and efficient. This is made possible by:– Premium fuel: designed for 92+ octane fuel to prevent knocking.
– Precision cooling: advanced cooling systems that manage the extreme heat.
Exhaust gas recirculation (EGR): Advanced cooled EGR systems take some inert exhaust gas and feed it back into the cylinders. This lowers the combustion temperature, which reduces energy lost to the cooling system and minimises knocking, allowing for that high compression ratio.High-pressure direct injection (GDI): Injecting fuel directly into the cylinder at very high pressure allows for a more precise, complete and cleaner burn.Electrification and the hybrid system (the biggest enabler):– Optimised operation: The hybrid system allows the engine to almost never run at inefficient speeds. It can be switched off at low speeds and, when on, it operates primarily in its “sweet spot” — a narrow band of RPM and load where it is most efficient (often where that 45% is measured).
– Load shifting: The electric motor handles transient loads (quick acceleration), allowing the engine to maintain a steady, efficient state. The engine doesn’t have to work hard to accelerate from a stop.
The role of the high-efficiency turbocharger
The turbocharger is not just for power; it is a crucial, efficiency device.
Energy recovery: a turbocharger is essentially an energy recovery system. It uses the waste heat and pressure from the exhaust gases which would otherwise be blown out of the tailpipe to spin a turbine that forces more air into the cylinders.Downsizing: This allows for “downsizing”, the use of a smaller, lighter engine that can produce the power of a larger naturally aspirated engine (e.g., a 2.5L) when needed, but with much better efficiency when under low load. In this context, Chinese makers invariably offer a 1.5 litre engine version because this attracts a low tax rate in their domestic market.High-efficiency design: A high-efficiency turbo, is designed with features to minimise lag and maximise flow.Ball bearings: These reduce friction, allowing the turbine to spool up faster.Optimised turbine/compressor scroll: Designed with advanced aerodynamics for less resistance and more flow.Electric assist (engineered decades ago by the German car industry): A small electric motor helps spool the turbo before exhaust gases build up, eliminating turbo lag and further improving response and efficiency.The downside to PHEVs fuel efficiency and fun-to-drive element is reliability, as observed in the latest JD Power study: 2024 U.S. Vehicle Dependability Study (VDS).
Together with other analysts, they point to one primary reason: complexity.
A PHEV is essentially two complete powertrains in one car: a full internal combustion engine (with its associated transmission, fuel system, exhaust, etc.) and a full electric drive system (with a battery, electric motor, power electronics and charging hardware). This doubles the number of systems that can potentially have issues compared to a traditional gasoline car or even a BEV.
Seeing as how PHEVs are offering unprecedented fuel-efficiency for combustion engines and they being an essential bridge for the transition to lower-carbon, if not zero-carbon land transport, will the Malaysian government support this technology while nurturing local manufacturing?
The Chinese government does this for PHEVs under its “New Energy Vehicle” policy, but always at a lower and diminishing rate than battery electric vehicles BEVs. Its target is still full electrification. - FMT
Yamin Vong can be contacted on Facebook at yamin.com.my.
The views expressed are those of the writer and do not necessarily reflect those of  MMKtT.

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