Volvo emission control

Volvo Penta has released a compact four-cylinder diesel that suits cruising yachts and cats and displacement cruisers. Known as the D2-55, it's a stroked version of the long-running two litre MD22L and MD22P. According to Volvo it complies with all current and known future exhaust emission regulations.

To achieve this compliance, Volvo has taken the unusual step (amongst the four-cylinder diesels currently available) of going back to indirect injection and opting for pushrod valve actuation instead of the belt-driven OHC in the MD22 series. I must confess that for relatively low-revving diesels I much prefer the inherent reliability of gear-driven or chain-driven camshafts to belt-driven units and for an engine that only reaches 3000 revs, there's really no need for OHC valve actuation.

The naturally-aspirated 2.2lt D2-55 has all the usual sensible Volvo engineering features such as a cast iron cylinder block and head and a five main bearing crankshaft with integral counterweights running in a rigid tunnel block crankcase.

Unusually (for those of us who were brought up with diesels having up to five rings), the high silicon aluminium pistons have only two cast iron chromium-faced compression rings and a single oil control ring, while replaceable hardened valve seats are fitted.

The in-line fuel injection pump is driven from the camshaft and incorporates a feed pump with hand primer, while the water-separating fuel filter and canister oil filter are both mounted on the same side.

The closed circuit (heat exchanger) cooling system features an easily-accessible seawater pump and impeller, a freshwater-cooled exhaust manifold and thermostat for constant cylinder head temperatures regardless of ambient or seawater temperature. Both the 14V, 60amp alternator and the 2.0kW starter motor are mounted high on the block away from bilgewater, and to reduce electrolysis between the engine and saildrive an electrical insulation is provided.

The alternator has voltage regulation and an electronic sensor for voltage drop compensation and glow plugs are fitted in the pre-combustion chambers for rapid cold starting.

The D2-55 is available with eight different transmission options, including a choice of hydraulic or mechanical gearboxes and a saildrive. The hydraulic box has an 8° down-angle at the output flange and is available with a trolling valve to reduce boatspeed when manoeuvring in marinas.

Mechanical boxes are offered with either the down-angle or a straight output flange and the saildrive allows for the engine to be mounted either forward or aft of it.

The gear ratios range from 2.29:1 to 2.71:1 in both right and left hand prop rotation for the hydraulic box but the down-angle mechanical unit is available in 2.23:1 for RH only and 2.74:1 in both directions. The RH and LH straight-output mechanical box has a strange choice of ratios in that none are compatible for handed installation and the saildrive is available with only a 2.19:1 ratio.

The 2.2 litre D2-55 has a maximum crankshaft output of 41kW (or 55.0hp at 1.0hp = 746W) and a propshaft output of 39kW or 52.3hp, both at 3000 revs. In comparison, the MD22L developed 48.9hp at 3000 revs and the MD22P developed 58.4hp at 4000 revs, both at the crankshaft.

The nearest Yanmar model, the two litre four-cylinder direct injection 4JH3(B)E, develops 55.2 crankshaft horsepower at 3800 revs.

By increasing the stroke from 89 to 100mm (the bore remains the same at 84mm) Volvo has significantly increased torque output over the two litre MD22 series. For example, the MD22L produced 124Nm (Newton metres) at 2200 revs and the MD22P 118Nm at 2500, whereas the D2-55 produces 135Nm at 2350 revs. And whereas the MD22L produced 112Nm at 1400 revs and the MD22P 110 at 1400, the D2-55 still produces 120Nm at the same revs.

The 4JH3(B)E produces 124Nm at 2000 revs and Yanmar provides a torque curve only as far as 1800 revs, where this model produces 123Nm compared to 133 at the same revs for the D2-55. By the time the Yanmar has reached 3800 revs the torque has diminished to only 105Nm, while at 3000 the D2-55 still produces 129Nm, so for an additional 20kg over the Yanmar the Volvo is by far the more powerful engine for its weight However, the D2-55 does lose out in fuel efficiency to both the MD22L and Yanmar competition. At Wide Open Throttle (WOT) the MD22L consumed 10.5lt/h and the Yanmar 12.3lt/h compared to 12.5 for the D2-55. Only the MD22P was more thirsty and consumed 14lt/h.

Based on a standard propeller power curve and throttled back to cruising revs of 2600 where the prop is absorbing 34hp, the D2-55 consumes 8lt/h, while at the same revs the MD22L developed 33.5hp and consumed 7lt/h. To produce the same horsepower as the D2-55, the MD22P would have to rev at 3200 and the Yanmar at 3300. The respective fuel consumptions would be 7.5 and 7.3lt/h so, as expected, opting for indirect injection for emissions compliance has reduced fuel efficiency.

Complete with a mechanical MS25A down-angle box (which I recommend for cruising yachts because of its relative simplicity) the D2-55 weighs 243kg compared to 235kg and 238kg respectively for the MD22L and MD22P. The D2-55 measures 917mm long, 544mm wide and 691mm high, whereas with a mechanical MS2A down-angle box both the MD22L and MD22P measured 887 x 591 x 677mm.

Fitted with a mechanical KM3A down-angle box, the Yanmar 4JH3(B)E measures 891 x 563 x 619mm.

A comprehensive level of equipment is supplied with the D2-55 and includes an instrument panel with the choice of a start button or key switch, an alarm system for monitoring oil pressure, coolant temperature and charging rate and a switch for alarm test and glow plug function. However, a tachometer with hour meter is optional and I would opt for the deluxe panel that has oil and temperature gauges and a voltmeter.

Volvo can also supply accessories such as an additional alternator, props and shafts, engine controls and steering, exhaust and hotwater systems, cooling water seacocks, strainers and hoses and PTO pulleys and universal brackets.

For more information on the D2-55, contact Eastern Engine, tel (07) 3899 1622, or visit the website: www.volvopenta.com.au