VW introduces new, more efficient TSI engine generation; Miller cycle with higher compression and electric VTG turbo
Volkswagen is presenting the latest generation of the EA211 TSI evo at the 37th International Vienna Motor Symposium. The first model in this future generation of spark ignition engines is the 1.5-liter TSI. The fuel-efficient and high-torque gasoline-fueled TSI engine is set to launch in late 2016, initially with outputs of 96 kW and 110 kW.
The main technology elements of the new EA211 TSI evo result in efficiency benefits of up to 10% compared with the previous 1.4l TSI (92 kW). The improvements in fuel economy take effect across a wide range of the engine map—i.e, they do not merely apply under test bench conditions but also impact everyday driving. Among the key new/revised technologies are:
Miller combustion cycle with a high compression ratio of 12.5:1
Turbocharger with electrically actuated variable turbine geometry (VTG)
Common-rail injection system with up to 350 bar pressure
Innovative thermal management
Cylinder deactivation (ACT)
APS-coated cylinder walls (atmospheric plasma spray)
The cylinder head has been extensively re-engineered. Initiatives include optimization of the water jacket for improved heat dissipation and adaptation of the valve angle and combustion chamber for the best possible execution of the Miller combustion process. The proven concept of the exhaust manifold integrated into the cylinder head has been retained. In contrast to the EA211, the intake camshaft is adjusted using a high-speed hydraulic camshaft actuator with a central control valve. The adjustment speed of up to 300° of crank angle (CA) per second enhances the dynamics of the cylinder-fill control.
Millerization and the VTG turbo. The Miller combustion cycle uses a higher expansion ratio than compression ratio (i.e., over-expansion) obtained by either early or late closing of the intake valves (EIVC and LIVC, respectively), and results in a smaller effective compression stroke; combustion and expansion proceed normally.
One effect of the Miller cycle is to reduce pumping losses, improving the thermal efficiency of the engine. The Miller cycle can also deliver hefty torque for a given displacement. Yet another effect is that it can be used to mitigate the propensity for knock in highly boosted engines.
Last year, Audi engineers introduced their then new series-production 2.0 TFSI gasoline turbocharged direct injection engine based on the Miller Cycle. (Earlier post.)
Volkswagen said that its implementation of the Miller combustion cycle is a key innovation in the new EA211 TSI evo. The resulting improvement in thermodynamic efficiency has been systematically implemented through four main development targets:
Increase in the geometric compression ratio to improve efficiency in customer-relevant operation.
Reduction of the final compression temperature through early intake valve closing and resulting expansion cooling in the intake stroke.
Optimization of the charge motion in the interests of rapid flame propagation to reduce knock tendencies at high specific loads.
Increase in charge density through efficient exhaust gas turbocharging.
A world-first for the TSI evo is the use of an exhaust gas turbocharger with electrically actuated variable turbine geometry (VTG).
Due to early intake valve closing in the Miller combustion cycle, volumetric efficiency is lower than for an engine with standard valve timing. Under partial load, the resulting de-throttling leads to a fuel-consumption benefit for the TSI evo.
High charge pressure balances out the effect of the inherently lower effective stroke volume to create high low-end torque. At low engine speeds in particular, this places very high demands on the turbocharging system. Through adaptation of turbine flow characteristics to match the operating points, an exhaust-gas turbocharger with variable turbine geometry presents the opportunity to provide very high turbine output and thus high charge pressure from low engine speeds.
The increased accumulation effect on the VTG turbine, in combination with a reduced moment of inertia in the turbocharger, additionally results in very spontaneous response characteristics. Compared with a 1.4l TSI (92 kW), the step change in load to the maximum torque takes place some 35 per cent faster. Overall, VTG technology forms an integral part of the TSI evo combustion process.
The indirect charge-air cooling has also been modified. In contrast to the EA211, the cooler is located in the pressure pipe, downstream of the compressor outlet and before the throttle valve, meaning it, too, is cooled. The new installation position made it possible to increase the size and performance of the cooler, while maintaining a very compact overall package. It is now able to reduce the temperature of the charge air to 15 Kelvin above that of the ambient air.
Injection system. The injection system is the first application of the fourth-generation Volkswagen direct-injection system. Optimization of the overall system and its components facilitated an increase in injection pressure to 350 bar. The resulting smaller droplet size improves mixture formation, leading to benefits such as a substantial reduction in particulate emissions.
The innovation of reducing the diameter of the injector tip to 6 mm, which is beneficial for integration into the combustion chamber, improves stiffness and reduces temperatures at the injector plate.
Thermal management. The new map-controlled cooling module provides the engine with efficient thermal management. Among other things, the cooling module ensures the water in the crankcase and the engine as a whole remains stationary during the warm-up phase. The resulting rapid engine warming improves heating in the car’s interior and reduces engine friction during the warm-up process. A further benefit of the map-controlled cooling module is that the engine can be cooled in close correlation with its requirements across the entire operating range.
Cylinder deactivation. Cylinder deactivation, another subassembly from the EA211 engine assembly kit, has been improved and is entering volume production with the TSI evo. This, too, benefits engine efficiency and is an important feature when it comes to the customer experience. It closes off the intake and exhaust valves of cylinders two and three up to the mid-load range, while at the same time deactivating fuel injection.
APS-coated cylinder walls. The cylinder liners in the aluminium crankcase for the 110 kW power variant are coated using the APS process (atmospheric plasma spray). Fine-grain spray powders combined with a specifically optimized grinding process lead to the creation of tiny lubrication pockets, which ensure that the piston rings glide smoothly with low friction and little wear.
Further benefits of this solution are the increased heat dissipation compared with cast iron, the resulting improvement in antiknock properties during combustion and improved corrosion resistance in respect of poor-quality fuels on global markets. APS technology has also demonstrated particularly good wear resistance in hybrid applications, whereby the cold engine is often started under higher loads.
Other features of the TSI evo include an extensive friction package. This encompasses a map-controlled, fully variable oil pump, polymer coating of the first main crankshaft bearing and a switch to low-viscosity 0W20 oil.