THE new Mercedes-Benz S320 CDI sedan adds an environmentally digestible alternative to the menu for the hallowed German brand's S-class flagship. It provides the parsimonious fuel economy and C02 emissions to help reduce its impact on the environment while not foregoing driving pleasure via impressive acceleration figures and a mountain of mid-range torque. The almost complete absence of diesel engine clatter will only go further to cement the legitimacy of such engines in a high-end luxury car.