The new Mercedes-Benz SLK: Passion meets efficiency - Daimler

Lightweight construction techniques and detailed improvements have alsoreduced in-engine friction considerably compared to the previous engine.Page 28Third-generation direct-injection systemSpray-guided direct petrol injection, which Mercedes-Benz was the first carmanufacturer to introduce in series production, has been developed further asa third generation. The system pressure is up to 200 bar, the pressure beingvariably optimised according to the engine's characteristic map. Completelynewly developed piezo-electric injectors allow up to five injections per intakestroke for the best possible mixture formation.The crystalline structure of the piezo-ceramic changes in microseconds underan electric voltage, and with a precision of just a few thousandths of amillimetre. The central component of a piezo-electric injector is the piezo-stack,which directly controls the metering needle. With a response time of just0.1 milliseconds, the fuel injection can be very sensitively and preciselyadjusted to the current load and engine speed, with a beneficial effect onemissions, fuel consumption and combustion noise.In the V6 unit, the multiple injections even in tiny quantities made possiblewith piezo-electric injection technology were used by Mercedes-Benz engineersto control a wider, usable characteristic map with the efficient lean-burnprocess, and to provide the conditions for further functions.As the first new operating mode, Mercedes-Benz engineers have developed"Homogeneous stratified combustion" (HOS). As the name implies, HOS is acombination of homogeneous lean-burn and classic stratified combustion. Withthe engine unthrottled, the first injection is sprayed into the intake stroke,forming a homogeneous basic mixture. Actual "stratified" injection takes placeduring the compression stroke before ignition, and is a single or doubleinjection depending on the characteristic map.Another new operating mode is known as "Homogeneous Split" (HSP). In thishomogeneous combustion process, more than 95 percent of the fuel is singlyor multiply injected, followed a very small "ignition" injection to stabilisecombustion. This is used when combustion conditions are difficult.Daimler Communications, 70546 Stuttgart/GermanyMercedes-Benz – A Daimler Brand