Renaults Hungarian Sidepod Fire

The silver canister is visible towards the front lower of the sidepod - via nextgen-auto.com

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

http://scarbsf1.wordpress.com/category/front-exit-exhaust/

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21 thoughts on “Renaults Hungarian Sidepod Fire

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  2. Great article as always!

    Thinking about the Renault car in pitstops has brought up another question (apologies if you’ve already addressed it). Does having a car with mid-mounted exhausts running at full revs in a pitstop interfere with the mechanics in any way? Do you think they’ve had to adjust their pitstop procedure to accommodate the car’s exhausts this year?

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  4. “asking teams to place this item in a more secure position” – if I was a driver, having seen a cylinder explode, I wouldn’t want to have one between my legs. Bye bye calf muscles.

  5. “…but instead a pneumatic pressure keeps the valves pressed open against the cam.”

    Surely you mean “pressed closed against the cam”?

  6. Scarbs,
    If you pause at ):16 sec into the fan’s video, while does the fire plume suddenly exit through the back of the diffuser..if it was a sidepod fire alone??

  7. I have a little experience of Lithium Ploymer battery fires from the RC Buggy scene. The fire AFTER the explosion really reaminds me of a LIPo fire,the browny coloured smoke that seems to be coming from deeper inside the chassis.

    Typical LiPo fire

    Imagine that on an F1 scale !

  8. Assuming this was a nitrogen reservoir of aluminium construction, and assuming they are not replaced at each race, it is not beyond the realms of possibility that fatigue of the pressure vessel from the act of charging it could have been a factor. This coupled with the thermal shock of using a liquid fire extinguisher. Given the extreme temperatures at various locations of the cars I was surprised that dry powder fire extinguishers were not used, as on high temp fires a liquid extinguishent, be it foam or water, will be broken down into oxygen and hydrogen among others things and fuel the fires intensity. Also with KERS being brought back this year it makes using anything other than powder an unnecessary added risk. Going back to the nitrogen reservoir, any idea if these incorporate a steel banding around the outside or an aramid weave that would reduce the damage of an explosion?

    • Aluminum becomes soft and lose strength when heated. This while the pressure inside the pressure vessel increase with the temperature. The maximum service temperatures of most aluminum alloys is just 150-250 degC.

      Thermal shock is probably less of an issue, aluminum usually don’t shatter when cooled.

    • Watch the video – those were dry powder extinguishers. Notice the dry powder sitting on the track after the first extinguisher shot. I’m surprised they use dry powder, as I understand it can play havoc with carbon fiber.

      • Yeah, you’re dead right, I was thinking of carbon dioxide extinguishers.

        Would dry powder have caused sufficient thermal shock for aluminium to shatter under pressure?

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  10. Good stuff Craig.

    A quick search on the web, however, suggests that, unlike many steels, aluminium alloys are actually very good under cryogenic conditions, and do not suffer a ductile-to-brittle transition at low temperatures. Here was one quote:

    “As temperature decreases below room temperature, not only do the static and fatigue strengths of all aluminum alloys increase, but also the ductility and toughness of most alloys increase as well. These properties make them excellent candidates for a variety of applications, including the Space Shuttle External Tank, arctic structures, and other structures and equipment operating at temperatures below zero.”

    Perhaps thermal shock is a different matter?

    • Aluminum has a very high coefficient of thermal expansion. This is NOT a cryogenic application – holding liquid nitrogen would be; this is pressurized gas at normal temperature (until the fire).

      • Indeed, but the fracture of the cylinder is said to have been caused by the cooling effect of the extinguishant, hence I initially wondered if the aluminium had suffered a ductile-to-brittle transition under transient cryogenic conditions. Cryogenic due to the extinguishant, not due to the nitrogen.

        I think the answer is the shear rate of temperature change (‘thermal shock’) caused the fracture.

  11. Craig, is in the regulations to have a pressure relief or thermal plugg on the tank. most nitrogen tanks have a temp pressure relief. Nitrogen remains pretty stable at high temps. The walls of that tank are pretty thick, I think the marshal was hit maybe with a carbon fibre piece. The marshal kept his leg (thank god).The tank could have discharge and blew out a releif. But still isn’t this there second fire? FEE hasn”t shown any real gains and seems to burn fast, instead of go fast.

  12. When first posted the video I saw was from a different web site. The explsion came out low, making me think it was a cooling hose for oil or water. I read in on your site that coolers have a 60 psi pressure limit. If it was oil that temp would have vapor locked thus the delay of fire. The fire was of low temp looks around 1200 to 1400 f, that would be enough for the radiator or hoses to blow out. The tank mounts high on discharge side of the radiator and still covered by body work during the fire. Nice pictures Craig.

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