Management of the engine’s noise characteristics has focused particularly on injector tick and combustion noise, which is controlled through the use of next-generation common rail technology, including ‘multiple-point’ injection and closed-loop injection control, which ensure that the combustion is smooth under all operating conditions.
The fuel quantity provided by each injector is controlled by a piezo actuator, which enables highly accurate fuel metering of up to five injections per cycle. These features provide an extremely fine spray of diesel fuel, which ensures the most uniform fuel-air mixture possible, resulting in a more complete combustion process. As a result, the diesel engine is able to achieve both high power and the desired emissions capability.
From the outset, the 2.7 twin-turbo Diesel engine was designed to meet future emissions levels. However, further advances in reducing emissions since the launch of the S-TYPE twin-turbo Diesel have been made through changes to the fuel injection system, utilising higher injection pressures and different injector spray patterns. The calibration of the electronically actuated turbochargers, the exhaust gas recirculation system and port deactivation have also been revised. With the addition of a Catalysed Diesel Particulate Filter (CDPF), the advanced design of the V6 engine ensures it exceeds Euro Stage IV emissions requirements.
Aiding both performance and emissions is a forced induction system, comprising twin-turbochargers with state-of-the-art electronic actuation. Traditionally, turbochargers are vacuum actuated, but this new form of rotary electric actuator gives a higher degree of control, providing benefits in the areas of emissions and transient engine performance, as well as in balancing performance and emissions between the two cylinder banks. The turbochargers are a low inertia type for quick, responsive, power delivery.
The high-grade aluminium alloy cylinder heads are equipped with four valves per cylinder and double overhead camshafts. This combination provides optimum induction and exhaust actuation, with attendant benefits in performance and emissions. The cylinder head design includes a port deactivation system and pistons with toroidal combustion chambers, producing a highly efficient combustion capability. A low - by diesel standards - compression ratio of 17.3:1 contributes to improved emissions quality, quieter combustion and compatibility with the engine’s unique forced induction system. In a diesel engine, reduced compression means less heat build-up in the piston bowl and more efficient fuel burn, resulting in lower levels of pollutants.
A revised secondary bulkhead structure has been introduced to the engine compartment of all XJ models - both diesel and petrol - to reduce interior noise levels by up to five decibels. The result is the most refined vehicle in its class for interior comfort.