Quoting "sources familiar with testimony to the investigation," FlightGlobal.com reports that air traffic controllers monitoring the takeoff noticed flames from one of the right hand engines at around the same time that the crew notified ATC that they were rejecting takeoff. The article adds that it is unclear which one of the engines was affected.
FlightGlobal.com also reports:
Tyre marks at the end of the runway and wheel tracks across the grass, extending to the wreckage site, suggest the aircraft was deviating to the right of the centreline as it overran. Brussels Airport has three runways.Here is the link to the entire article: Engine fire alert preceded Kalitta 747F rejected take-off - FlightGlobal.com
Its two parallels are longer than the accident runway, but the source states that runway 20 was always the “planned runway” for the 25 May flight.
The aircraft had been bound for Bahrain with 76t of cargo, and the source points out that runway 20 – which has a length of 2,984m (9,790ft) – was more than adequate for the type, particularly given its relatively light load.