All the secrets of Alfa Romeo 'MultiAir' technology

[alfagtv100 (Biggus)]

Original article can be found at:
http://www.duemotori.com/news/auto_news/35556_All_the_secrets_of_Alfa_Romeo_MultiAir_technology.php

Alfa Romeo proudly introduces MultiAir technology to the world on its latest creation, the Alfa Romeo MiTo. The forerunner of the new family is the MultiAir 1.4 engine, available in 3 different power levels on the new model: 105 HP, 135 HP and 170 HP.
This marks a significant generational leap compared to current petrol engines, as occurred in 1997 with the Common Rail applied to diesel power units and introduced to the world for the first time on the Alfa Romeo 156. Now comes the turn of the 'sportiest Mini ever' to pick up the baton and mark a true leap of technology: the MultiAir system takes the controlled ignition engine to previously unthinkable levels of efficiency. This is achieved due to the principle underpinning this new technology: the possibility of continuously adjusting the main elements that guarantee optimum combustion at any speed and under all driving conditions.

In particular, the possibility of managing the most appropriate moment for opening and closing the intake valve has optimised the engine's volumetric efficiency, bringing benefits in terms of maximum torque delivery, particularly at low speed: compared to a conventional 120 HP turbo petrol engine, the same engine with MultiAir achieves an increase in maximum power (135 HP) without penalising torque and response at low engine speed (5000 rpm).
The introduction of MultiAir technology therefore makes the Alfa Romeo MiTo even more agile and spirited due to the power and torque increases possible with the new power units. The engines also guarantee a significant reduction in fuel consumption and  polluting emissions for benefits in terms of running costs and respect for the environment.

For example, the flexibility and speed of response guaranteed by the MultiAir system make it possible to manage engine load by means of the intake valves, eliminating the use of the throttle valve to benefit combustion efficiency at partial loads and hence fuel consumption. Suffice it to say that the same power unit reduces fuel consumption over an NEDC cycle by up to 10% compared to a conventional 120 HP turbo petrol unit. 

The new power units represent a significant point of departure from the current petrol engine scenario. For example, compared to a conventional petrol engine of the same capacity, MultiAir guarantees an increase in power (up to 10%) and torque (up to15%), in addition to a significant reduction in fuel consumption (up to 10%) and emissions of CO 2  (up to 10%), particulate (up to 40%) and NOx (up to 60%).

The heart of the MultiAir is a new electrohydraulic valve management system that allows a reduction in fuel consumption (by controlling air directly via the engine intake valves, without using the throttle) and polluting emissions (via combustion control). As befits a flag-bearer for the downsizing concept, the MultiAir is a versatile system that is easily applicable to all petrol engines that may potentially be developed for diesel engines in the future.
Load management by means of the intake valves also means that combustion can also optimised even during motorway use. The area within which the mixture is made richer has been greatly limited by exploiting system characteristics: the fuel-air mixture is still stoichiometric at 150 km/h, for example with particularly low specific consumption.

The new generation of MultiAir power units has also been designed to enhance the car set-up options available via the Alfa DNA selector to ensure the most effective response to the driver's expectations and the different road conditions.

Why MultiAir

Over recent years, the controlled ignition engine has undergone continual development to regain competitiveness with present-day turbodiesel engines that have revolutionised the world scenario due to the advent of Common Rail technology.

Until now, petrol engines were subject to two limitations that had to be removed to ensure the necessary leap in efficiency. Firstly, the throttle valve restriction: a system for modulating the power required by the driver that is simple yet inefficient due to the consequent load loss, above all at speeds when the valve is hardly opened, i.e, within the service range typical of normal driving.

The second limitation was represented by the reduced freedom of operation of the intake valves, which often meant engineers had to configure the personality of the power unit by choosing between a sporty timing setting or a set-up more conscious of fuel consumption, or prioritising comfort and torque at intermediate speeds or focusing on power at high speeds and the lengthening more typical of a lively drive.

These two limitations were finally removed with the advent of MultiAir technology: the credit for this goes to the ingenious system patented by FPT – Fiat Powertrain Technologies, which allows the valve lift and opening time to be managed in accordance with numerous operating parameters that are analysed and processed in real time, thus allowing the engine to choose the best possible configuration to meet the driver's requests moment by moment.

The new power units featuring MultiAir technology are therefore standard bearers for the concept of downsizing, which combines applied efficiency with peak performance. The resulting benefits are truly numerous when compared with conventional engines with the same cylinder capacity: including an increase in maximum power (up to 10%), an increase in torque (up to 15%) at low speed and during transients due to the advanced power unit operating parameter control strategies. And more: a reduction in fuel consumption of more than 10% (due to doing away with pumping loss and the accurate calibration of parameters optimising fuel combustion) and CO2 emissions (up to 10%), particulate (up to 40%) and NOx (up to 60%), due to optimisation of  valve control strategies during the engine intake phase and internal exhaust gas recycling.

In other words, outstanding performance, complemented by a very prompt response to accelerator commands due to the constant air pressure upstream of the cylinders combined with extremely fast control of the intake valves. Not to mention the fact that the MultiAir engines fitted to the Alfa Romeo MiTo are the first to feature the innovative "Start&Stop" system that automatically turns off the power unit when the car is at a standstill (at a traffic light, for example) maintaining all vehicle systems in operation to ensure the greatest comfort to all occupants.

The new MultiAir engines are designed from the development stage to further enhance the Alfa DNA selector, the device that allows the personality of the Alfa Romeo MiTo to be adapted to the driver's needs and different road conditions. More specifically, when the selector is in "Dynamic" position, the engine response is immediate, delivery is substantial due to the overboost, the Electronic Q2 allows corners to be tackled in complete safety, ensuring a performance in line with the sporty spirit of all Alfa Romeo cars.

With the selector in "Normal", position, everyday driving becomes fun without giving up on comfort and a smooth drive. Fuel consumption is also minimised. Under slippery conditions, active safety can be further increased by selecting an "All Weather" position that alerts all the car's safety systems  (including VDC and Electronic Q2), which are ready to leap into action in case of need for a smoother engine response.

How the MultiAir system works

The project aim was ambitious: to allow the intake valves to be controlled without their strict dependency on the camshaft, which has nearly always represented the only way to ensure their operation over more than 100 years of technological development. Achieving this goal was possible only by the valuable wealth of technological and human experience built up over the years by the Alfa Romeo brand and Fiat Powertrain Technologies on ordinary roads and race tracks.

It is therefore no exaggeration to claim that MultiAir is a distillate of the exceptional technological pathway that allowed the Italian motoring industry to make its name on roads and racetracks throughout the world. It is enough to remind ourselves of some of these innovations, which stand as milestones in the history of the motor car: production of the first aluminium twin shaft engine on a mass produced car (Alfa Romeo Giulia), the use of twin variable valve timing and the Twin Spark (Alfa Romeo 75), the first modular engine (Alfetta) and the Common Rail system (Alfa Romeo 156). And now the Alfa Romeo MiTo extends this extraordinary list of achievements with the MultiAir system, a versatile technology that is easily applicable to all petrol engines that may potentially be developed for diesel engines in the future.

On conventional petrol engines, load is controlled by modulating the density of air taken into the cylinders by means of the throttle valve. This determines an efficiency loss known as "pumping work". The MultiAir system does away with this loss. The load is controlled by adjusting the volume of air added at constant density temperature due to direct and extremely flexible control of the intake valves.

The system controls the intake valves by means of an electrohydraulic system: a piston operated by a mechanical cam is connected to the intake valve by means of a hydraulic chamber controlled by a normally open solenoid valve.

Two situations may arise: when the solenoid valve is closed, the fluid in the hydraulic chamber acts as a solid body and transmits the lift law imposed by the mechanical intake cam to the intake valves. In the second case, however, when the solenoid valveis open, fluid in the hydraulic chamber can flow out toward a low-pressure circuit: as a consequence, the intake valves no longer follow the mechanical cam profile and close under the effect of the two intake spring force. The final part of the valve closure travel is managed by a dedicated hydraulic brake that ensures a controlled approach stage under all service conditions.
It is therefore possible to obtain innumerable intake valve opening profiles with ease by adjusting the solenoid valve opening and closure times. In this way, engine load is controlled directly via the intake valves and no longer via the throttle valve.

The behaviour of the MultiAir in three different situations is described below.
1) Maximum power delivery stage: the solenoid valve is permanently closed and the valves are fully opened by following the entire profile of the mechanical cam, which is specifically optimised for power at high speeds (long intake valve opening intervals).
2) At low rpm and full load: the solenoid valve opens ahead of the theoretical cam profile, closing the intake valve prematurely. This does away with undesirable flow back into the manifold, maximising the air mass trapped in the cylinders.
3) Under partial engine load conditions: the solenoid valve opens during the intake travel to partly open the valves and control the incoming air mass on the basis of the torque requirement. Alternatively, the valves may be partly opened to close the solenoid wvalveith a delay in relation to the beginning of the theoretical profile guaranteed by the mechanical cam. In this case, the speed of the air flow entering the cylinders is higher and generates a particularly high level of swirl in the cylinders. It is also possible to combine these two operating modes for the same intake event: this gives rise to the "Multilift" effect, which increases swirl and combustion speed at very low loads and speeds.

To sum up, the flexibility and speed of response guaranteed by the MultiAir system make it possible to manage engine load by means of the intake valves, eliminating the use of the throttle valve to benefit combustion efficiency at partial loads and hence fuel consumption.

[Brad M]

Nice conclusion ...

[Sheldon McIntosh]

 

[pep105]

Thanks Biggus for the technical explaination of MultiArse err MultiAir technology

P.S 200 posts whoo hoo !

[Brad M]

P.S 200 posts whoo hoo !

ditto the ... whoo hoo