Introduction
After more than two years’ debate, six months of driving impressions and with the clock ticking towards the demise of Euro-3 in October, Mercedes-Benz has become the first manufacturer to offer its greenest engines for independent scrutiny. Following all the advertising and kidology by the manufacturers about which combustion system is best, SCR (selective catalytic reduction) with AdBlue is first off the blocks. The Germans skipped Euro-4 for this test and went straight for the jugular. With the Euro-5 deadline in the post – along with road tolls based on emission charging – the greenest engines will be favoured when it comes to being fleeced by the government of the day. And with such a short time between its launch and its supersession by Euro-5, Euro-4 might well prove redundant.
As well as fuel economy and payload, potential operators of any new truck need to consider issues like asset ownership and depreciation. Predicting a Euro-5 Axor’s worth three years down the road is one step too far at the moment. But we reckon it will command decent residuals because that Euro-5 status is set to make it cheaper to run than Euro-3 models, regardless of its cost per mile. Enough speculation: let’s get down to the nitty gritty. The Euro-5 Axor supplied for test is an 1840LS, and if it looks familiar we’re not surprised as this is a Tesco truck.
Product Profile
The Euro-5 engine that powers it is a Mercedes-Benz OM457LA 11.97-litre, straight-six, DI, charge-cooled turbo-diesel with a 90-litre AdBlue tank. It produces 395hp from 1,900rpm with peak torque of 2,000Nm at 1,100rpm. This is the middle of three engine options; the others are 350 and 430hp with 1,850 and 2,100Nm torque respectively.
Standard transmission is Merc’s eight-speed synchro box with an additional crawler. It’s has a direct-drive top, as does the optional 16-speeder, with an axle ratio of 3.08:1.
The engine spec is identical to the familiar Euro-3 lump apart from that all important SCR system that injects AdBlue into the catalytic converter as needed. The harder the engine is working, the more AdBlue is added. SCR meets Euro-4 and 5 by way of an ‘after burn’ process. The manufacturers have removed the established emission-control system that met Euro-3 and raised the combustion temperature. Burning the fuel outright removes the particulates at source but increases oxide and nitrogen production; fortunately these gases are relatively harmless.
This system makes the engine closer to Euro-2 in many ways, and on average Euro-2 engines produced better fuel consumption than their Euro-3 successors. As a result, other things being equal, Euro-4 and 5 engines should beat Euro-3 fuel consumption.
That advantage is offset by the cost of AdBlue, of course. And if you’re rubbing your hands and contemplating running Euro-5 wagons without AdBlue, forget it. In time Euro-5 engines will feature diagnostic electronics which will automatically reduce power output when the AdBlue runs out. In the meantime, your truck will pick up an immediate prohibition if that AdBlue tank is found to be empty.
The Euro-4/5 alternative to SCR is EGR (exhaust gas recirculation). EGR engines have a lower combustion temperature, relying on particulate traps to hit those all-important emissions standards. Until we’ve taken an EGR-engined truck round the CM test route we won’t waste your time with idle speculation on which system offers better fuel consumption. Tesco trucks are standard fleet-spec apart from a wire-mesh platform over the chassis, an air-powered Jost sliding fifth wheel, a reversing alarm and windows in the rear and sides of the sleeper-cab.
Productivity
The CM database of 40-tonners and around the 400hp mark isn’t extensive; for the past three years our artic tests have reflected the industry’s emphasis on top-power 44 tonners. Nevertheless the tests we have completed at this weight offer a decent overview of Euro-3 drivelines over the past four years, so we can consider the likely advantage, if any, in upgrading your current truck.
In terms of fuel consumption the first signs are promising. If a Euro-5 engine can match Euro-2 fuel economy, which many operators reckon was the best thing since the Euro rating system began, then things bode well for SCR. And our two-day test confirms that raising the combustion temperature does in fact improve like-for-like fuel consumption.
This Euro-5 Axor notched up 8.97mpg over the two days of the test. Over the common section of the route (shared with our old test route) it managed 9.30mpg – more than 0.5mpg better than the Euro-3 Axor 184- with an identical engine tested over three days in 2002.
However, that saving is reduced by the cost of AdBlue. We used 8.10 litres during the test, equating to 3.38% of diesel consumption; only time will tell if this is a typical figure. In any case, this Euro-5 Axor managed 9.34mpg and 8.76mpg on days one and two of our test.
When we tested a Euro-3 Scania R124 420HPI it racked up 8.91 mpg over two days. Its strong point was easy A-roads while the Axor Euro-5 proved better on tougher A-road sections and motorway. The Daf CF85 380, tested in 2002 over three days, produced 8.99mpg on the common section.
