18-06-2013, 04:00 PM
Multi Air Engine
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INTRODUCTION
Fiat Group was one of the first manufacturers to adopt what has become the increasingly common practice of improving official fuel economy and CO2 emissions by creating a small forced-induction engine which uses fuel at a modest rate when the turbocharger isn't operating but produces similar power to a much larger unit when it is. In 2010, it has taken the idea a stage further by introducing various versions the 1.4-litre MultiAir petrol engine to the Punto Evo and Alfa Romeo MiTo ranges.
In the Geneva Auto Show to launch a new engine technology which could ultimately be as important as the common rail diesel technology it invented 15 years ago. Dubbed MultiAir, the hydraulically-actuated variable valve timing (VVT) technology was first announced as a concept two years ago, and offers a more controllable flow of air during the combustion cycle in comparison with mechanical VVT systems. Vastly reduced fuel consumption and emmissions plus significantly more power are claimed, and the technology is even more effective when used with a supercharger or a diesel engine.
Fiat claims Multiair is a fundamental breakthrough in petrol engine design that will dramatically cut fuel consumption, as well as significantly boosting power and torque, cutting carbon dioxide emissions by between 10 and 25 percent, and up to a 60 percent reduction in other engine pollutants.
This higher output will allow Fiat to replace larger engines with smaller, more efficient ones, and the company's 1.0 liter and 1.4 liter engines will be the first to get the new technology, along with a new 900cc twin cylinder engine.
Unlike the common rail diesel technology, which it sold to Bosch during a financial crisis, and has regreted ever since, FIAT will not be relinquishing ownership of the new Multiair system, having announced it will license it to other manufacturers or provide entire engines
History
The Multiair technology took over a decade to get finished. The vice president of Fiat Powertrain Research & Development Rinaldo Rinolfi led the team who developed the technology. Development costs were over $100 million. There was also delay in development, in the time (2000-2005) when Fiat was in partnership with General Motors.
Other systems
Currently ready alternatives to industrialization do not exist, but there are under development also totally camless systems. The Valvetronic system used by BMW allows the valve timing and lift to be varied but not the cam profile. The ability to vary the latter is characteristic of camless and the Multiair systems.
Development of the Fiat MultiAir system
In the last decade, the development of Common Rail technology for diesel engines marked a breakthrough in the passenger car market. To be equally competitive in the field of petrol engines, Fiat Group decided to follow the same approach and focus on breakthrough technologies.
The aim was to provide customers with substantial benefits in terms of fuel economy and driving pleasure, while maintaining the engine’s intrinsic refinement, based on a smooth combustion process and on light structures and components.
The key parameter to control diesel engine combustion and therefore performance, emissions and fuel consumption, is the quantity and characteristics of the fuel injected into the cylinders. That is the reason why the Common Rail electronic diesel fuel injection system was such a fundamental breakthrough in direct injection diesel engine technology.
However, the key to controlling petrol engine combustion, and therefore performance, emissions and fuel consumption is the quantity and characteristics of the fresh air charge in the cylinders. In conventional petrol engines the air mass trapped in the cylinders is controlled by keeping the intake valve opening constant and adjusting upstream pressure through a throttle valve. One of the drawbacks of this simple conventional mechanical control is that the engine wastes about 10 per cent of the input energy in pumping the air charge from a lower intake pressure to the atmospheric exhaust pressure.
MultiAir Technology: how it works
The operating principle of the system, applied to intake valves, is the following: a piston, moved by a mechanical intake camshaft, is connected to the intake valve through a hydraulic chamber, which is controlled by a normally open on/off solenoid valve.
When the solenoid valve is closed, the oil in the hydraulic chamber behaves like a solid body and transmits to the intake valves the lift schedule imposed by the mechanical intake camshaft.
When the solenoid valve is open, the hydraulic chamber and the intake valves are de-coupled; the intake valves do not follow the intake camshaft anymore and close under the valve spring action.
The final part of the valve closing stroke is controlled by a dedicated hydraulic brake, to ensure a soft and regular landing phase in any engine operating conditions.
Further Potential of MultiAir Technology
All breakthrough technologies open a new world of further potential benefits, which are usually not fully exploited in the first generation.
Common Rail technology, a Fiat Group worldwide premiere in 1997, paved the way to more than a decade of further technological evolutions such as MultiJet for multiple injections, small diesel engines, and the recent Modular Injection technology, soon to be launched on the market.
Similarly, MultiAir technology will pave the way to further technological evolutions for petrol engines:
Integration of the MultiAir Direct air mass control with direct petrol Injection to further improve transient response and fuel economy. Introduction of more advanced multiple valve opening strategies to further reduce emissions. Innovative engine-turbocharger matching to control trapped air mass through a combination of optimum boost pressure and valve opening strategies.
While electronic petrol injection developed in the ’70s and Common Rail developed in the ’90s were fuel-specific breakthrough technologies, MultiAir Electronic Valve Control technology can be applied to all internal combustion engines whatever fuel they burn.
MultiAir, initially developed for spark ignition engines burning light fuel ranging from petrol to natural gas and hydrogen, also has wide potential for diesel engine emissions reduction.