Volvo Penta D12

Volvo Penta's new D12 incorporates some features not evident in comparable engines.

The D12 has the same technology of its smaller counterparts, such as a four-valve head. But unusually for a diesel in the 500-550kW range, it has an overhead camshaft and one-piece cylinder-head instead of the pushrods and individual cylinder-heads of its direct German and US competition.

The one-piece cylinder-head reduces the possibility of gasket leakage, which can occur with individual cylinder-heads. But, of course, the downside is that it rules out the ability to replace individual components should metal fatigue occur in one of these heads.

Like its direct MAN D28 competition (reviewed in last month's Trade-A-Boat) the D12's injectors are located centrally in the combustion chambers between the valves of the crossflow cylinder-head. But Volvo Penta has opted for unit injectors instead of the traditional fuel-rail design with a fuel pump driven by the timing gear.

According to Volvo Penta, the fuel-injection set-up allows each cylinder to be individually controlled by the Electronic Diesel Control (EDC) engine management system, which overcomes the small differences in fuel supply to the cylinders when a fuel-rail system is used. This improves idle quality and reduces servicing time because any errors or operating malfunctions are stored in the memory, cylinder by cylinder. Combined with the eight-hole injectors used, the D12 complies with current IMO exhaust emission regulations.

As with earlier EDC systems, the D12 monitors engine revs and total operating hours, engine and gearbox oil pressure, engine oil and coolant temperature and exhaust gas/charge air temperature, which indicates engine load. The EDC varies injection timing according to engine load and the air/fuel ratio according to barometric pressure.

The EDC itself has been improved over earlier designs and like MAN's MMDS system uses a serial data cable between the management computer at the engine and the one at each helmstation. The system allows owners to add new functions by updating the software in the computer boxes, whereas in earlier EDC systems this technique is used in the second helmstation onwards.

Each helmstation has an information display showing instant engine data on a single LCD screen and with the standard sensors fitted also shows stats such as fuel usage (litres per hour). Combined with a log function the hull speed is also shown, enabling the helmsman to calculate the most fuel-efficient speed or litres consumed for distance travelled.

Interestingly if a minor engine malfunction occurs the helmsman's calculations are not altered, but the information is still stored in the EDC system's memory for later downloading by a laptop computer. The new information display and control panel are optional with all other Volvo Penta EDC engines.

The direct-injection D12 develops 515kW at 2300 revs from 12.13lt and has a bore of 131mm and a stroke of 150mm. The maximum fuel consumption is 136lt/hr, the same as MAN's 515kW D28. In the maximum torque range of 1400-1800 revs, the full-load fuel consumption is 105-130lt/hr and based on an average propeller power curve the consumption drops to 39-68lt/hr.

At 2800Nm (at 1500 revs) the D12 develops a massive 12% more torque than the D28, although by 1800 revs this has dropped to 10% more. But at 1000 revs the torque is 1300Nm - 24% down on the D28 at the same revs.

Due to the discrepancies in torque between the D12 and D28, consider the kilowatts being developed in the maximum torque range under full-load conditions. In the 1400-1800 rev range the D12 develops 400-500kW, whereas in this range the D28 develops 370-475kW and consumes 90-115lt/hr. Thus in this rev range the D28 is theoretically about 8% more fuel-efficient.

Surprisingly for an engine having a one-piece cylinder-head and OHC, which reduces weight over pushrods, the D12 is one the heaviest engines in its kilowatt range. Sans gearbox, it weighs in at 1400kg dry - 15% more than the D28 and 19% over the 12lt Cat 3196, which develops 492kW.

The standard single-speed ZF IRM325A-E electronically-shifted gearbox with down-angled output shaft adds 170kg to the D12's weight.

As for bobtail (sans gearbox) measurements the D12 is 1790mm long, 1027mm wide and 1177mm high. So it's a much bulkier engine than the D28. The 107mm (height) and 158mm (width) difference can have a substantial effect when trying to shoehorn an engine into an existing engineroom, both in terms of saloon sole height and twin-engine side access.

The D12's weight may be considered by some to be a minus when compared to the Cat and MAN competition. When quizzed on this, Volvo technicians told Trade-A-Boat that the trade-off in performance (a claimed 0.5-1kt difference in top speed based on a weight difference of 200kg) was more than countered by the overall refinement the new powerplant delivers.

Whatever, there's no doubt Volvo Penta has put a lot of effort into packaging the D12 and the mid-range torque it develops is a real plus compared to its competition!

For more information on the D12, contact Graeme Avers at Eastern Engine, tel (07) 3899 1622.

Please note: A kilowatt rating is mentioned in this review instead of horsepower because the latter output can vary between US and European measurements. The US standard is 746W for each horsepower, which means the D12 develops 690hp. But based on the European (and Japanese PS) system of 736 watts per horsepower, the D12 develops 700hp.