UK: GE Transportation has published the results of a series of back-to-back fuel consumption comparisons between its Class 70 PowerHaul locomotive and the GM-EMD Class 66. This follows a study on improving the fuel efficiency of diesel traction undertaken by Ricardo for the Department for Transport.

Ricardo put forward a proposal to reduce the fuel consumption of the Class 66 by 30%. It was estimated that this suite of modifications could save £53m a year in fuel costs across the Class 66 fleet at a cost of £100 000 per locomotive.

In addition to having a more efficient four-stroke engine, the more recent Class 70 design already incorporates as standard several of the upgrades suggested by Ricardo. These include an auxiliary power unit which allows the main engine to be shut down, rather than kept idling, and enables the use of automatic engine stop and start, similar to the system fitted to some cars.

With the Class 70 now challenging the Class 66 in the European freight market, fuel efficiency is a potential sales tool. But, unlike most diesel engine manufacturers, EMD rarely states specific fuel consumption figures in its technical literature.

Rail Business Intelligence has found a 1982 conference paper in which EMD quoted the specific fuel consumption at full power for its previous generation of engine as 212 g/kWh. The published figure for the Class 70 engine is 192 g/kWh.

To provide an independent comparison, GE commissioned Ricardo to oversee back-to-back testing of the two locomotive designs using the static load banks at Wabtec Brush Traction in Loughborough. As Ricardo's Head of Rail Vehicle Technology Jim Buchanan told Rail Business Intelligence, this was an 'extremely rare opportunity' to evaluate the dominant UK freight locomotive against a 'state-of-the-art' unit which incorporated many of the improvements proposed by Ricardo in its study for DfT.

For the test, a mid-life Class 66 was borrowed from a 'current UK rail freight operator'. As an older design it complies with UIC 1 emissions standards, producing up to 12 g/kWh of NOx. The Class 70 engine complies with EU Stage IIIa regulations which specify a maximum of 7·4 g/kWh.

Typical Class 66 duty cycles were obtained from freight operators which provided the time the engine spent in each power notch. Using measured fuel consumption, the overall fuel consumption could be calculated for each locomotive over identical duties.

This showed that on like-for-like duties the Class 70 would consume 18% less fuel than the Class 66. That does not include fuel savings from AESS and the use of current produced during dynamic braking to power onboard auxiliaries.

In preparing its original report, Ricardo had been unable to obtain the specific fuel consumption for the Class 66 engine. The only information available was from a UIC report based on UK data.

This showed the EMD power unit as having slightly better sfc than the MTU 4000 Series which has a published sfc of 194 g/kWh. The Class 70 engine has a quoted sfc of 192 g/kWh and recorded 190·1 g/kWh at full power in the recent tests.

According to Ricardo, the Class 66 recorded 'in the region of 225 g/kWh' at full power. The report notes 'the fact that the measured fuel consumption of the older Class 66 was noticeably higher' than the estimates in the report for DfT 'makes the case for the retrofitting of new technology packages in the absence of vehicle replacement all the more compelling'.

Test procedure

Fuel used during the load bank tests was weighed with an accuracy of around ±0·02%. Power from the main and auxiliary alternators was measured plus, in the case of the Class 66, the power absorbed by the mechanically-driven auxiliaries. Compressed air was supplied to both locomotives to prevent the air compressors starting up which would have interfered with the constant power runs.

Each locomotive was run several times in each power notch to ensure consistent measurement of fuel consumption and power output. After corrections for ambient temperature during the tests, alternator efficiencies and fuel energy content, Ricardo calculated the specific fuel consumption for each controller power notch.