Jaguar Introduces New 3.0L Diesel for European Market

31 December 2008

The new AJ-V6D. Click to enlarge.

Jaguar is introducing a new 3.0-liter diesel engine—the AJ-V6D Gen III—in two power levels in its XF Diesel S sedan for the European market. The new V6 engine, derived from the 2.7-liter diesel, improves fuel economy by 12% and produces 10% less CO₂ (179 g/km) than the 2.7L, while increasing power by 33%. The new 3.0L engines are Euro-5 compliant.

The 275PS (271 hp, 202 kW) version delivers 600 Nm of torque, accelerates the sedan from 0-60 mph in 5.9 seconds, and has combined fuel economy of 35 mpg US (42 mpg UK, 6.7 L/100km)—a 12% improvement in fuel economy over the 2.7-liter V6 diesel. The engine is also available in a 240PS (237 hp, 177 kW) variant, with 16% more power and 15% more torque than the 2.7-liter diesel.

Torque buildup (top) and torque gradient (bottom) for the AJ-V6D Gen III compared to the 2.7L diesel at 1,500 rpm. Click to enlarge.

A key feature of the new engine is the parallel sequential turbocharger system, the first of its type to be fitted to a V-engine. Delivering high torque throughout the entire engine rev range, improved throttle response and low CO₂ emissions, the twin-turbochargers work sequentially to deliver 61% more torque from 1,500 rpm than the 2.7L diesel.

For most day-to-day driving, including highway cruising, a variable-geometry primary turbocharger does all the work, while a smaller, fixed-geometry, secondary turbo is dormant, saving energy and improving efficiency. When the engine revs climb above 2,800rpm, the secondary turbo is brought on line within 300 milliseconds with no discernible turbo-lag or power-step.

Valves under the control of the engine management system isolate the secondary turbocharger both from the exhaust stream and the engine inlet tract when it is not required to alleviate pumping losses.

Some twin-turbo systems rely on a smaller turbo for primary use, only using a larger turbo when higher power is required. Though effective, this has the disadvantage of raised exhaust pressure and increased pumping losses, Jaguar says. The Jaguar system uses a larger, variable-geometry turbocharger more of the time, which not only reduces pumping losses, but also improves fuel consumption and CO₂ emissions.

Jaguar engineers particularly focused on the issue of turbocharger lag at low engine speeds. The new AJ-V6D Gen III 3.0-liter diesels deliver 500 Nm of torque 500 milliseconds from idle.

A new commonrail fuel-injection system delivers up to five injections on each cycle at a pressure of 2,000 bar. Each injector has seven holes. The piezo crystals in Jaguar’s new injectors are fitted nearer the tip—i.e., they are mounted deeper inside the engine providing better sound insulation and quieter operation.

Another new feature of the third-generation fuel-injection system is the metering mode. Traditional diesel commonrail fuel pumps oversupply the injectors, with the surplus being returned to the fuel tank. During this process, fuel temperature increases and cooling it again consumes energy. In metering mode, the pump delivers fuel to the injectors only at the rate required. Consequentially, there is no rise in fuel temperature and no wasted energy.

The two cylinder heads, with four valves per cylinder, are made from aluminium and the cylinder block is made from compact graphite iron (CGI). The higher tensile strength of CGI makes it possible to cast a smaller block; some 80mm shorter than a conventional grey cast iron equivalent.

The new, water-cooled, exhaust gas recirculation system (EGR) is more efficient and consumes less power than the 2.7-liter unit. The valves that allow exhaust gas into the system are located on the hot side of the engine nearest the exhaust manifolds; these valves never cool while the engine is running, so there is no condensation of combustion deposits which occurs on engines fitted with cold side valves, hence the EGR system always works at maximum efficiency. Since the EGR cooling is so effective, exhaust gasses can bypass the system and return to the exhaust pipes, allowing faster engine warm-up from start-up and reducing emissions still further.

The Jaguar XF diesel. Click to enlarge.

Euro 5 emissions compliance is achieved through using conventional diesel oxidation catalysts and diesel particulate filters (DPFs). NO_x levels are reduced at source through the combustion system design, the addition of the new commonrail injection system and the new EGR system with by-pass. As a result, specialized NO_X exhaust after-treatment is unnecessary, avoiding a potential cost and the need to use additional precious metals in the exhaust system.

The XF sedan mates the new 3.0L engine with a six-speed ZF 6HP28 automatic transmission.