Nice - A new era for the internal combustion engine
A new internal combustion engine addresses the drawbacks of petrol and diesel designs. As a result, it cuts both fuel consumption and carbon dioxide emissions. The project, NICE, was supported by the European Commission.
A European Union-funded project, called ‘New integrated combustion system for future passenger car engines’, or ‘NICE’, aimed to develop a new integrated combustion system. Involving 26 partners, and coordinated by DaimlerChrysler, the project contributed to achieving the highest fuel conversion efficiencyindependent of the type of fuel.
In particular, one sub-project taken on by a group of partners within the NICE consortium, led by Centro Ricerche Fiat, focused on turbocharged spark-ignited gasoline engines. They developed the application of an advanced system of variable valve actuation using electro-hydraulic technology, which improves on similar systems by allowing multiple valve opening and closing in a single cycle and in being simple and cheap enough to be mounted on the lowest cost segments of the car market.
Engines for automotive vehicles are increasingly under several pressures: to cut fuel consumption, greenhouse gas (GHG) emissions and polluting emissions, and deliver attractive performance and costs for drivers. To date, it has been difficult to optimise engine designs so as to meet all these goals at the same time.
In previous research projects, internal combustion engines for petrol-driven vehicles (using the ‘Otto-cycle’) had been designed to cut noxious emissions to very low levels. Unfortunately they had greater fuel consumption than diesels. On the other hand, diesel engine designs have been able to lower fuel consumption, but only at the cost of higher emissions of acidifying gasses and particles. To complicate things even more, along with petrol and diesel, bio-fuels have now been added to the mix of fuels available to drivers.
NICE solutions brought to market
The NICE team tried to combine the best of both worlds and with considerable success: "When operated in a compact car, the project's technologies led to an average improvement in fuel economy and CO2 of around 10% when compared with the baseline engine " says Massimo Ferrera of CRF, which is developing the application of this technology to natural gas engines as coordinator of the current InGas project.
The team also concluded that engine efficiency could improve even further (up to 25% in city driving) through integration of this technology with turbo charging and engine downsizing – shifting the engine ‘operating point’ (i.e. the rhythm at which it operates) to one with higher efficiency.
The technology is now being marketed by Fiat in their Twin Air and MultiAir engines. "We are talking of mass market models which sell in the hundred thousands, not only sport and premium cars, as in the past", comments Maurizio Maggiore from the Transport Directorate of the European Commission, "and this will deliver a real impact on greenhouse gas emissions".
In the future, it will also help in optimising the use of low CO2 fuels such as natural gas and bio-fuels, but "it can provide fuel savings even to truck diesels "says Ferrera, which is involved in the forthcoming CORE project to develop this application.
Optimising the engine cycle
How does the technology work? The basic internal combustion engine cycle relies on the timing of the firing of the sparkplug (to ignite the fuel and air which drives the piston) and the opening and closing of the intake and exhaust valves (to let fuel/air in and exhaust gasses out). The amount of air entering the engine cylinder is normally regulated through a throttle. This requires energy, which then affects fuel consumption – particularly when driving at the low speeds typical of city driving.
In its simplest form the engine’s valves are opened and closed via camshafts. A cam, a shaped off-centre wheel, pushes the valves up and down (and therefore open and shut) as it rotates.
Through this simple method the valves’ opening and closing are synchronised with the combustion cycle of the engine. However, when the engine runs at different speeds or with different loads, a single basic cycle is not always optimal – leading to the engine working harder than necessary, wasting fuel and driving up CO2 emissions.
The NICE project’s electro-hydraulic system is mounted on the intake valve and allows the timing of the valve’s opening and closing to be controlled independently according to different strategies, such as ‘Early intake valve closing’ or ‘Late intake valve closing’. These can be used to optimise fuel consumption in different circumstances, such as when the engine is running under low or medium loads, or for improving its performance in cold weather. The engine’s running can therefore be modified to meet all these conditions without use of the throttle to determine the quantity of air, and therefore without unnecessary loss of energy.
The new system connects the intake valve to the camshaft via a high-pressure oil chamber, instead of directly. The oil chamber is then controlled electronically via a switch. When closed, the switch runs the engine normally by keeping the oil under pressure, which transmits the camshaft motion in full through the oil chamber to provide full lift to the intake valve as usual.
If ‘Early intake valve closing’ is desired, however, the switch can be opened so oil flows out of the oil chamber, reducing pressure. As a result, the intake valve is no longer coupled directly to the movements of the camshaft and is closed, by a spring, earlier in the cycle than in the full-lift mode.
Similarly, the intake valve can also be made to close later than normally in the cycle via the switch. The engine thus has a much more flexible range of combustion cycles, whereby the timing can be altered to optimise the combustion of the fuel – leading to both lower consumption and reduced emissions.