HOW LOW CAN WE GO? INNOVATION Center housing HOW LOW Oil inlet Turbo wheel Twin-scoll turbine CAN WE GO? housing with integrated Figure 2. Turbochargers such as this are making, exhaust gas manifold for example, four-cylinder engines as powerful as their six-cylinder predecessors DOWNSIZING THE INTERNAL Compressor wheel COMBUSTION ENGINE Compressor conventional engine twice its size. The team Radial Thrust housing has also installed this downsized engine to bearing bearing a series production Volkswagen Passat with excellent results. Fuel economy is exceptional Figure 1. Turbocharger cutaway labels the main assemblies within the turbocharger © Bosch Mahle Turbo Systems at 49 mpg and the vehicle can accelerate In the race to cut carbon from 80 to 120 km/h in nine seconds. Bosch Mahle Turbo Systems expects to produce dioxide emissions and The last year has seen a flurry of petrol- Consumers want to drive more fuel-efficient more than one million performance- powered medium-sized vehicles downsizing vehicles, but not at the expense of engine optimised turbochargers by 2015. boost fuel efficiency, there from their usual six cylinders to just four. performance. Innovations from components is broad consensus among Earlier this year, Korean car manufacturer suppliers have been crucial in ensuring that Hyundai released a revamped Sonata with power is not lost in the process. TURBOCHARGING EXPLAINED vehicle manufacturers that four cylinders. Germany-based Audi soon In both petrol and diesel vehicles, the downsizing the internal followed with a four-cylinder powered turbocharger comprises two assemblies: A4 and Volvo, of Sweden, now plans to AVOIDING POWER LOSSES a centrifugal compressor powered by a combustion engine should downsize all its engines to four cylinders and Despite having a lower displacement, the turbine that is driven by the engine’s exhaust be a part of the process. 2.0 litres by 2014. Indeed, there are plans to performance of a downsized engine can gases (see Figures 1 and 2). Hot exhaust downsize to three cylinders and eventually, be maintained by injecting more air into gases flow through the turbine’s wheel Dr Martin Knopf, managing two. Why? Engine downsizing is the most its combustion chamber to burn additional blades, accelerating the turbine and driving director of Bosch Mahle effective measure to cut fuel consumption fuel. This is made possible by turbocharging, the compressor. and carbon dioxide emissions. which provides the engine with the mass These turbines are made from high- Turbo Systems, explains Downsizing is a simple concept; replace of air needed to ensure highly efficient and temperature resistant nickel alloys, and how the exhaust gas turbo a larger engine with a smaller version, with clean combustion. can withstand temperatures in excess of a lower displacement. The downsized In 2008, Bosch teamed up with Germany- 1000°C and accelerate to speeds upwards of charger is the enabler for engines of tomorrow will have fewer, smaller based Mahle to form Bosch Mahle Turbo 280,000 revolutions per minute. downsizing concepts. cylinders, so the volume swept by pistons as Systems to develop modern turbocharging The compressor itself comprises an they pump up and down inside is reduced. systems for new petrol and diesel engines impeller and a diffuser, housed in the This will reduce friction, thermal losses and in passenger cars and commercial vehicles. compressor casing. The precision-milled the mass moved, boosting fuel economy Progress since then has been rapid. aluminium alloy impeller draws in air, and cutting carbon dioxide emissions. A turbocharger developed by the joint accelerating it to a high velocity before Diesel engines have already undergone venture has recently been fitted into forcing it towards the diffuser. The aggressive downsizing – up to 40% – Mahle’s three-cylinder petrol engine. diffuser slows the fast-moving air, raising over the last decade and more stringent The engine can produce 160 horsepower the pressure and temperature in the emissions legislations see this trend moving and 286 Nm from a displacement of only compressor housing, and compressing the Small gasoline engine with electrical waste gate actuator being tested on hot gas test bench © MAHLE over to petrol engines. 1.2 litres, matching the performance of a air before it is directed to the engine. In 36 INGENIA INGENIA ISSUE 49 DECEMBER 2011 37 HOW LOW CAN WE GO? INNOVATION this way, more air can be injected into the diesel engine is different. Developers at a lower speed, reducing rotational speed. second at medium speeds. At high speeds, the combustion chamber, ready to burn have introduced ‘variable turbine geometry’ Controlling the velocity of exhaust gases in control software switches off the smaller the additional fuel needed to maintain to the diesel turbo-charger in which a set this way gives a high turbine efficiency. charger leaving only the larger turbocharger engine power. of adjustable vanes in the exhaust housing operating. This approach delivers high torque To prevent the turbocharger from control gas flow across the turbine. at all speeds; there is no turbo-lag and the overcharging at high engine speeds – and At low engine speeds, turbine speed MORE ROOM FOR DIESEL diesel engine performs more powerfully. also to maintain torque at lower engine is maintained or increased by minimising But following a decade of downsizing, can speeds – the flow of exhaust gases through the cross-section of the vanes’ inlet. This diesel engines be designed to even lower the turbine and compressor is carefully ensures the exhaust gas flows quickly ON THE ROAD AHEAD displacements? Developers believe so Thanks to the ongoing developments in controlled. In a petrol engine, at high through the inlet, hitting the turbine blades and are looking to improve the common- turbocharging technology, the internal engine speeds, a waste gate is opened to at high speed and raising the rotational rail fuel injection system to boost engine combustion engine will retain its dominant divert part of the exhaust gas flow away speed. Meanwhile at higher engine speeds, performance even further. position over alternatives, such as all-electric from the turbine. This decreases pressure inlet cross-section increases so the exhaust Fuel injection is the system used to mix and hybrid drives, with the proportion of in the compressor housing and prevents gases hit the interior of the turbine blades fuel with air in a diesel internal combustion turbocharged engines found in passenger overcharging (see Breaking the knock limit). cars set to rise steadily. Thanks to extreme Meanwhile at low engine speeds, the downsizing, the petrol and diesel engines of waste-gate will close so that the entire Thanks to extreme downsizing, the petrol and diesel the future could have just two cylinders and exhaust flow can drive the turbine and engines of the future could have just two cylinders and a a displacement of lower than a litre. the compressor. These turbochargers are Emissions targets are also fuelling research also designed to provide ‘over-boost,’ a displacement of lower than a litre. into alternative carbon-cutting technologies. temporary, excessive increase in pressure Engineers are currently exploring combustion for when, say, the driver is accelerating. control using combustion chamber pressure The mechanism to control gas flow to Direct injection in the diesel engine – extreme downsizing makes even lower fuel consumption and sensors as well as looking to recover energy carbon dioxide emissions possible. Bosch sees potential for a further 30% reduction from exhaust heat to increase automotive efficiencies further. These technologies BREAKING THE engine. In common rail fuel injection 2011. In fact, engineers are already working will contribute significantly to more KNOCK LIMIT systems, all injectors are supplied fuel by on a 2,500 bar system to help boost engine economical driving and ensure car For decades, the so-called ‘knock limit’ has the common fuel rail, in which fuel is stored power further. manufacturers will meet the stringent hampered efforts to improve the efficiency at high pressure (see Figure 3). Raising this And so-called ‘two-stage turbocharging’ emissions targets of tomorrow. of the gasoline engine. Measures that could pressure improves control of fuel injection, could also be used in downsized diesel have made the engine far more efficient so fuel can be injected into the engine engines to maintain performance and solve BIOGRAPHY would have caused ‘knock’; spontaneous with greater accuracy and frequency, the well-known problem of ‘turbo-lag’. Dr Martin Knopf has been Managing fuel combustion that causes a metallic increasing power. When accelerating in a vehicle from low Director of Bosch Mahle Turbo Systems clanging noise and can damage the engine. Injection systems have developed at speed, a single turbocharger may not inject since 2008. He studied technical For example at high engine speeds, breathtaking speeds over the last decade enough air to the engine for combustion, engineering and began his career at MTU when knock is more likely, fuel is injected with higher fuel pressures and faster, and the car ‘hesitates’. A two-stage system Friedrichshafen in 1992. He has been at directly to the hot combustion chamber more accurate dosing of fuel helping overcomes this problem. Bosch since 2001 starting off as Director where it quickly evaporates, cooling manufacturers to meet tougher emissions Here a smaller high-pressure turbocharger, responsible for engine management the existing fuel and gases and making standards. Many of today’s common rail used to rapidly raise pressure levels and systems and combustion analysis in the central research department. spontaneous combustion less likely. Direct diesel systems have fuel pressures up to pressure build-up in the compressor casing, injection pushes the knock limit towards 1,800 bar, but there are plans to start series is connected to a larger low-pressure Figure 3. The common rail system: in 1989, Audi was the first automobile manufacturer to use the higher loads and greater degrees of electronically controlled axial piston distributor injection pump from Bosch.