The Irony
It starts off from various global summits regarding emission levels from automobiles around the world. The norms getting more and more strict every year, and with good reason. The ozone layer is at stake, so the CO2 levels have to be minimized. The anvil falls on the powertrain.How ironic is it that the engines are being 'down'sized, yet the very cars and people which they have to tug are getting fatter. People want more power, comfortable seats, power-'everything', space in the boot, 'SUV' sized proportions....yet it should only sip fuel every now and then and never break down! Not to mention, meet the emission levels as well in the process. Hatchbacks are getting as wide as the streets themselves! How about downsizing vehicle dimensions as well? 'Kei' cars like the Toyota IQ and our very own TATA Nano should be the future if you don't want to spend half the day commuting!
Downsizing
How much is enough? How far can you scale down an engine and yet produce the same or yet more power than where you started from?Welcome to the world of downsizing and forced induction everyone!
The idea that smaller engines using forced induction such as turbo or supercharger to produce more power and torque by burning the fuel efficiently using lots of air is not new.
The turbo, which was developed by Swiss engineer Alfred Buchi was used by the French to in their Renault powered aircraft during WWI. It has excellent altitude compensating ability, thanks to the compressor that forces compressed air in the engine cylinders. For reciprocating engines, it has been a boon ever since. Mechanically powered superchargers have also become popular for tuning cars and aircraft engines (reciprocating type).
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| Rolls Royce Merlin V12 Engine |
However, 'inertia' has been the turbo's 'Achilles heel' since it is driven by the engine's exhaust gas stream and the turbine takes time to fully spool up (to start rotating at the rated rpm). Hence, it takes some time to actually provide some 'boost' to the engine i.e. air at the desired pressure for enhanced volumetric efficiency. The term 'turbo-lag' comes into the picture, which has been the anti-christ in the auto industry ever since the turbocharger was conceived.
Auto makers started using various techniques like 'Variable Geometry' (which directs the exhaust stream on to the turbine blades in a variable and adaptive manner so that the turbine responds more quickly to the throttle pedal) and 'smaller turbos', which have lesser inertia and hence spool up quickly.
Performance car manufacturers used the turbo to great extent to extract every ounce of power from the existing engines rather than building a bespoke engine (and incur the huge tooling costs). Supercars like the Jaguar XJ220 of the power crazed '80s is a perfect example. It used a twin-turbo V6 instead of a larger V8 or V12 as used by the Italians and the Germans. Even top level motorsport like Formula 1 used the turbos.
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| Variable Geometry Turbo unit |
Performance car manufacturers used the turbo to great extent to extract every ounce of power from the existing engines rather than building a bespoke engine (and incur the huge tooling costs). Supercars like the Jaguar XJ220 of the power crazed '80s is a perfect example. It used a twin-turbo V6 instead of a larger V8 or V12 as used by the Italians and the Germans. Even top level motorsport like Formula 1 used the turbos.
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| Jaguar XJ220 |
In the previous decade, however, things started to move quickly with auto manufacturers reducing the engine volumes and using forced induction to bring the emission levels down and increase the thermal efficiency of the powertrain. It all started with the Toyota Yaris 1.0L engine which won several engine of the year awards in 1999. It powered the hatchback Yaris which was a perfect example of a Japanese 'kei' car. The kei cars were a Japanese government initiative to produce shorter wheelbase city cars which could solve the traffic clogging problems faced in mega-cities like Tokyo.
VW was the first manufacturer to make significant in-roads in this field however, with the 'Twincharger' concept, which combines turbo and supercharging to optimize engine performance across the rev range for the 1.4L R4 gasoline engine. They called it 'TSi' and it is still the benchmark to which all the OEM manufacturers look up to even today. It comprises of a roots type supercharger which is driven by the engine at 1.5X speed and feeds to a turbo unit, which further multiplies torque at higher revs. This arrangement nearly eliminates turbo-lag at lower revs. At high speeds, the supercharger unit is disconnected by a clutch and the intake air is fed directly fed to the turbo unit, which provides the boost. Hence, the engine need not drive the supercharger and incur parasitic losses. Also, the fuel is directly injected in the cylinders through a high pressure common rail and special injectors for efficient charge ratio and induction. It operates at a lean setting for maximum fuel economy and is installed in various VW group vehicles.
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| VW 1.4 TSi engine |
The Ford Motor Company recently brought the 'EcoBoost' engine to the market, which uses a 1.0L R3 turbocharged gasoline engine with cast iron block (to reduce engine heat up time) which also incorporates the exhaust manifold and an eccentric flywheel to reduce the vibrations. The turbo helps achieve a high specific power output, comparable to larger displacement engines. It won six engine of the year awards in 2013.
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| Ford 1.0L 3 cylinder EcoBoost engine |
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| The valve arrangement in the EcoBoost cylinder head along with the fuel injector near the intake valves which enhance the swirl of the intake charge |
In the performance car industry, BMW recently reduced the volume and cut two cylinders from its V10 which powered the E92 M5 and created a 'TwinPower Turbo' 4.4L V8, which had even more power and torque, expecially at lower rev range, with almost similar response time as the V10, yet with reduced emissions.
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| BMW 4.4L TwinPower V8 |
Also, when it comes to turbo-diesels however, BMW has been the benchmark through the years with its 2.0L and 3.0L turbo-diesels winning awards across the world. They also introduced the concept of a twin-turbo which has a small and a large turbine, each used at different engine revs to reduce the spool up time, to reduce turbo-lag. It delivers the torque figures equivalent of a medium-capacity V8.
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| BMW 3.0L R6 twin-turbo diesel |
The Future
It is clear that emission levels and depleting natural resources will force the auto industry into re-thinking about powertrains on a completely different level. Alternate fuels like synthetic gasoline, bio-diesel, electric-hybrid power and fuel cells. Currently, the engine development centers are focusing more on enhancing the efficiency of the powertrain by using hybrids, primarily gasoline-electric. The key points are extended range, low emissions and better specific power output as well.
A classic case in point is McLaren's in-house developed 3.8L twin-turbo V8 which gives an output of 730ps and is coupled with a battery pack which boosts the output to a mind boggling 900+ps. They key aspect of this powertrain is that it uses the battery pack for multiple things (than for storing and delivering energy alone). It is also used to even out the torque across the rev range, acts as the alternator and removes the need for a separate battery source to start the engine! The emission levels are extremely low for an engine of this category.
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| McLaren M838T 3.8L V8 with KERS |
The P1 is proof that even supercars of the future will use downsized powertrains with electric power boost for extended range and to lower the emission levels.
