Update: Lotus Renault GP, have provided me with this response from Technical Director James Alison.
Three days after the incident on Nick’s car, has the team identified the reason why it caught fire after the pitstop?
J.A.: As with most accidents, several incidents combined to cause the fire that Nick suffered in Hungary. First of all, we ran a slightly different engine mapping strategy in qualifying, which produced hotter than normal exhausts. We believe that this elevated temperature and caused a preliminary crack in the exhaust pipe. We presume that the crack then propagated during the laps to the pitstop – this was not evident to us as we believe that the failure occurred upstream of the place where we have a temperature sensor. We believe that Nick then came in with a partially failed exhaust. This pitstop took longer than normal, the engine was left at high rpm for 6.3 sec, waiting for the tyre change to be completed. Under these conditions, a lot of excess fuel always ends up in the exhausts and their temperature rises at around 100°C/sec. This temperature rise was enough to finish off the partially failed pipe and to start a moderate fire under the bodywork.
There was an explosion shortly after Nick got out of the car, on the left. What was it?
J.A.: This was caused by the air bottle which supplies the air valves in the engine. It has overheated in the fire and failed.
Will you have to modify the car before Spa and if yes, is the August factory shutdown a handicap?
J.A.: The incident was highly undesirable, as it has caused us to write off a chassis. We will take steps prior to the next race to reduce the likelihood of a further fire and to ensure that the air bottle cannot overheat. We are in touch with the FIA both to provide them with a full report of the incident and also to explain to them the actions we are taking to prevent a reoccurrence.
As Nick Heidfeld made a pit stop at the Hungarian GP, there was a problem with one of his wheel nuts. This kept the car stationery for an extra 10-12 seconds. In readiness to leave the pit, Heidfeld kept the engine pegged at maximum revs. This extra delay was enough for the exhaust to start to overheat the surrounding bodywork. Without the usual pit fans blowing air over the bodywork, the carbon fibre soon started to smoke and then caught fire. Heidfeld was then released from the pit, as the wheel nut was properly fastened. Sparks were being blown from the car as he sped down the pitlane, this was the action of the exhaust blowing the fragments of the burning carbon fibre bodywork and not electrical sparks as some have speculated. The airflow over the bodywork only fed the flames and by the time he was at the pit lane exit his sidepod was well alight. As it was the bodywork itself that was on fire, the flames were on the outside of the sidepod and looked perhaps more alarming than was actually the case. Bodywork fires are not uncommon and teams have well rehearsed drills to meet the car in the pitlane with the pit fans and a precautionary fire extinguisher. Although it’s fair to say these sorts of fires are normally prevented by detail work to the shape and heat shielding of components early in the cars testing. Particularly around the exhaust which is the greatest source of heat within the sidepod. This year’s unusually long faired-in exhausts contribute a greater risk and the Forward exhaust exit (FEE) of the Renault only adds to the proximity of the exhaust to bodywork. With more conventional exhaust blown diffusers (EBDs), the exhausts are run along the floor to ahead of the rear tyre; these are slightly easier to manage. Additionally the heat shielded ducting for the Renault FEE, also provide a route for flames to exit out of the front of the sidepod, making the flames in closer proximity to the driver. This isn’t to say the Renault FEE is inherently unsafe. Any F1 cars bodywork left to overheat will see the flames rapidly spread across the skin of the cars sidepod bodywork.
What made Heidfelds fire more concerning was the apparently explosive moment when debris and gasses were blown out from the cars sidepod as the marshals sprayed extinguisher foam over the burning bodywork.
As the R31 came to rest, the driver jumped out and the fire marshals arrived from a post a few meters up the track. Two marshals tackled the blaze, running from behind the car to around the front to direct foam over the sidepods. As the first marshal carried on towards the rear of the car, the second marshal arrived at the front of the sidepods. Then there was this burst of debris and gas from the front of the sidepod. This appeared to slightly injure the marshal who limped around to the rear of the car. Renault have confirmed “he is ok. No injury. We are sending him a nice gift”. Shrapnel from the burst lay several meters away from the car in the pitlane exit lane. As we’ve seen fire’s are relatively rare in F1, oil fires being the more common and spectacular, but it’s very rare for a burning car to have this sort of violent moment.
Sidepods contain a multitude of systems; many items being solely in the left or right hand sidepods, rarely are any internals symmetrical left to right.
Typical components in this area are.
• Water radiator (LHS)
• Oil radiator (RHS)
• Hydraulic reservoir (varies)
• Nitrogen cylinder for the engine Pneumatic valve return system (varies)
• KERS battery water radiator (RHS)
• SECU, PCU, Battery, Lap time beacon (typically RHS)
• KERS PCU (RHS)
It’s important to note, sidepods do not contain the KERS batteries or the MGU. Also the gearbox oil and hydraulic fluid coolers are mounted atop the gearbox. There is very in the of little hydraulic systems being in the front of the sidepods, only the lines for the power steering passes this far forward in the car.
Seeing the explosion was not backed up with a further blaze of burning oil or steam from water radiators, its unlikely these burst in the fire. Then as most of the electronics are in the right hand sidepod, again these can be discounted. This leaves the obvious exception of the nitrogen cylinder. This is required as F1 engines do not use valve springs but instead a pneumatic pressure keeps the valves pressed open against the cam. In order to provide this pressure and as the system loses a little pressure during the race, a pressurised chamber maintains the required pressure. This comes in the form of a ~half litre aluminium cylinder. (Circled red – twitpic.com/5yycsi )
On most F1 cars and indeed Renaults all the way up to last year’s R30, teams mount these small cylinders inside the cockpit to protect them from crash or fire damage. Renaults R30 placed this on the hand side of the car, down on the small amount of floor between the driver’s seat and the side of the monocoque. But this location is not mandated by the regulations. Pictures of the R31 left-hand sidepod without bodywork, show there is an aluminium cylinder placed in the front section of sidepod. This transpires to be the nitrogen cylinder for the engine pneumatic valves. Probably because Renault had to create a slimmer monocoque to claw back the radiator volume lost to the routing of the FEE, they slimmed the monocoque and fond no space next to the driver’s seat to mount the cylinder and placed it outside on the radiator ducting instead. When this aluminium cylinder was heated in the flames and then suddenly cooled by the marshals extinguisher, the casing shattered sending the pressurised gas out in a hail of debris. This failure of a pressurised aluminium structure could also be the water radiator failing, while some rumours point to this the lack of the plume of steam ejecting from the sidepods after the initial blast, suggests to me this is unlikely. But to be clear, this wasn;t a chemical explosion, merely the failure of the casing of a pressurised vessel. as nitrogen is both intert and not liable to high rates of the thermal expansion
Comment by the team to news websites seems to back this theory up http://www.gpupdate.net/en/f1-news/265636/heidfeld-s-fire-caused-by-overheating-exhausts/ . Although I have yet to have direct confirmation from a source within Renault.
Seeing this was the first instance of such an occurrence that I can recall, I would imagine this might be examined by the FIA and technical directive issues asking teams to place this item in a more secure position to protect it and track officials from a similar incident.
More analysis of Renaults Front Exit Exhaust