|Mercedes-Benz CLS 350 CGI|
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Following intensive development work, Mercedes-Benz is now presenting the world's first petrol engine with spray-guided direct injection. The 215 kW/292 hp six-cylinder engine will go on the market in the second half of 2006 in the CLS-Class. In the European driving cycle, this innovative injection technology from Mercedes-Benz achieves fuel consumption improvements of ten per cent over the highly efficient V6 petrol engine with port injection and fully variable valve timing: the figures for the CLS 350 CGI are 9.1 - 9.3 litres per 100 km. Thus Mercedes-Benz has succeeded in combining a substantial increase in output with a significant increase in fuel economy.
This pioneering injection system is another trend-setting technology from Mercedes-Benz. It achieves much better fuel efficiency, and thus also higher thermodynamic dynamic efficiency, than conventional wall-guided direct injection systems. The new system will form the basis for future engine development work in this output class.
The new Mercedes-Benz six-cylinder engine achieves near-total combustion, which results in reduced emissions. A further important advantage of the CGI engine is stratified charge operation, an operating mode during which the engine is run with high excess air and thus excellent fuel efficiency. Now, thanks to multiple injection, it is for the first time possible to extend this lean-burn operating mode to higher rpm and load ranges too. During each compression stroke, a series of injections takes place, spaced just fractions of a second apart. This has the effect of significantly improving mixture formation, combustion and fuel consumption. Where previously stratified charge operation was only possible in the low part-load range, the new Mercedes direct-injection engine can still operate in this lean-burn stratified mode at speeds in excess of 120 km/h. When driving on main roads and motorways at largely constant speed and with proper anticipation, the CGI engine outperforms the fuel economy of the six-cylinder engine with conventional injection technology by up to 1.5 litres per 100 km, a saving of up to 15 per cent.
Low fuel consumption and excellent power delivery are never at odds on the new Mercedes-Benz direct petrol injection model. On the contrary, the engine delivers 15 kW/20 hp more power than the conventional-injection V6 and four percent more torque. With fuel consumption of 9.1 - 9.3 litres per 100 kilometres (NEDC combined cycle), the four-door Coupé has a range of approximately 870 kilometres on one tank filling.
The most important components of the innovative spray-guided direct petrol injection system are the fast-acting, high-precision piezoelectric injectors, which are responsible for virtually all the advances associated with this pioneering combustion technology. The piezoelectric valves have injectors which open outwards to create an annular gap just a few microns wide. This gap shapes the fuel jet and produces a uniform, hollow cone-shaped spray pattern. The microsecond response times of the piezoelectric injectors provide the basis for delivering multiple injections per compression stroke, and thus for lean-burn operation. By allowing flexible and efficient control of the combustion process they play a key part in ensuring the engine's outstanding fuel efficiency.
With the aid of fluid dynamics simulations, the pistons have been designed with special piston bowl geometry which concentrates the lean mixture in the area around the spark plug and prevents it from spreading out towards the cylinder wall. The piston shape plays its part in ensuring near-total combustion, low fuel consumption and low emissions. A high-pressure pump and downstream fuel rail and pressure control valve are responsible for delivering the fuel and regulating the quantity supplied. The peak fuel pressure in this system is 200 bar - around 50 times the fuel pressure in a conventional petrol injection system. The injection system also features a water-cooled heat exchanger to cool the fuel.
The Mercedes-developed combustion process featuring multiple closely spaced injections on each compression stroke also results in smoother operation and improved emissions performance. Measurements show that engine-out hydrocarbon emissions in the warm-up phase are almost halved. Furthermore, since the injection and combustion processes can be actively controlled, it is also possible to raise temperatures in the exhaust manifold and thus speed catalytic converter warm-up. Just eleven seconds after starting from cold, the direct petrol injection engine reaches an exhaust temperature of over 700 degrees Celsius. Emissions are controlled by two close-coupled three-way catalytic converters with linear oxygen sensor control, which goes into operation immediately after the engine starts from cold.
To reduce nitrogen oxide emissions, Mercedes-Benz has adopted a two-part strategy. This comprises, firstly, dual electrically controlled and cooled exhaust gas recirculation which, depending on engine operating conditions, redirects up to 40 per cent of the exhaust gases back into the cylinders. Secondly, it also comprises two underfloor NOx adsorber catalytic converter. Under lean operating conditions, these converters adsorb the nitrogen oxides. Periodically, during brief regeneration pulses, the nitrogen oxides are then desorbed, reacting with other exhaust gas constituents to form harmless nitrogen. Sensors upstream and downstream of the catalytic converters monitor their operation.
In addition, the new CGI engine also incorporates the same unique package of high-tech features as its conventional-injection counterpart. This includes four-valve cylinder heads, variable intake and exhaust camshaft timing, two-stage intake manifolds, balancer shafts and intelligent thermal management with an electronically controlled thermostat. The crankcase and cylinder heads are of aluminium and the cylinders and cylinder liners are of low-friction, thermally resistant, lightweight aluminium-silicon alloy.
All fuel-carrying components of the CGI engine are of high-grade steel or brass; the rails in the area of the two cylinder banks and the housing of the high-pressure pump are of forged high-grade steel.
The new CLS 350 CGI is designed to operate on sulphur-free unleaded premium fuel and its state-of-the-art technology gives it the potential to adapt to emissions standards of the future. In Western Europe, the CLS direct petrol injection model will replace the current CLS 350.
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|Article||Image gallery (9)||Specifications|