Scavenge Fire

Macphail
18th August 2009, 21:55
Scavenge Fires...

I have experienced many scavenge fires, the BF vessel Clytoneous was so bad that it had a scavenge fire alarm switch next to the manoeuvring stand, had one in the Suez canal, delayed the convoy , Clytoneous was “Black Balled”, always last to go through .
A contributory factor to the scavenge fire is poorly maintained fuel valves (injectors).
On a scavenge inspection, the heavily sludged space was the one with the defective fuel valves, the 3rd Engineer was the fuel valve man, incompetent 3rd engineer, good chance of a scavenge fire.
Sailed as 3rd Engineer on the Larchbank, no scavenge fires, I loved the small CAV injectors.
Did have one on the gas ship Gazana, firework display, hot burning soot embers dropping down on No 4 Tank dome.

http://www.shipsnostalgia.com/gallery/showphoto.php/photo/190994

John.

makko
18th August 2009, 22:28
Hi John,
There are a lot of contributory factors that can lead to the occurence of a scavenge fire but "bad housekeeping" is one of the more notorious!

Although I never personally sailed on them, several colleagues commented that the Bay boats were quite a nightmare, suffering regularly from scavenge fires after re-engining. I was led to believe that it was because the engines were installed on a slope to match the existing prop shafts and the twin 8 cylinder Sulzers (Thx Wharferat!) were finicky with regard low rpm and short movements during berthing. Maybe someone with direct experience would care to comment.

Regards,
Dave

wharferat
19th August 2009, 08:48
As Macpahail says, good housekeeping had a significant effect on preventing scavenge fires.
I had 5 trips on the Liverpool Bays & personally was aware of less than that number of scavenge fires. (Re-engined with 2 x 8RND90M). the worst engines I've sailed with for scavenge fires were MAN KZ 70/120's. Under piston scavenge valves, very dirty round the back, & unless running at near full power most of the time, they tended to get very dirty in the scavenge trunking, a full days work for 6 men to clean once a month.
We did find on one ship, Mistral, that by gritting our teeth & hanging in there, raising the maximum allowed exhaust temp from 400 degrees to 450, our scavenge pressure improved significantly, this in turn led to a cleaner engine (scavenge belt & ports), & in time the exhaust temps dropped. Also, as the ship had quite a few days in port at each end of the run, as 2/E I started checking the fuel v/v's throughout the engine & this also helped a lot.

For those not of an engineering persuasion, raising the max exhaust temps allowed us to put more fuel thro' the engine, in turn, more exhaust gas to drive the turbo chargers, ergo, more scavenge air.

Satanic Mechanic
19th August 2009, 14:40
Rules for the prevention of Scavange Fires:

1. Cleanliness
2. Cleanliness in the scavenge space
3. Cleanliness when overhauling Fuel Valves
4. More cleanliness
5. Maintenance
6. Maintenance of Fuel Valves
7. Maintenance of Pistons
8. Cleanliness when maintaining
9. CLO to be reduced to optimum
10. When you do this to the CLO - do it cleanly

I hold it as a point of pride I never had a scavenge fire from the day I went 3/E onwards. Even after my OCD had been treated(Thumb)

Macphail
20th August 2009, 22:08
The piston problem could be blow past into a dirty scavenge, broken ring on a particular unit with a defective fuel valve. The old double acters with Alfred Holt where famous for the scavenge fires. Promoted to fourth engineer on the Glenorchy 1963, first time as senior on the watch, on the 8 to 12, 2200 hrs, the Chinese fireman delivered the peanut butter toast and green tea for a break, enjoying, the port engine started panting, looked up, a very black cloud of smoke descending, Scavenge Fire, slowed the Port Engine to Slow Ahead, Starboard Engine to Half Ahead, increased the cylinder lubrication on the hot unit to maximum, placed a large bucket filled with water under the scavenge drain and opened it fully, after every thing had cooled down and stabilised, the scavenge was cleaned out .

SM. Last statement… ditto

John.

J Boyde
21st August 2009, 08:42
Two scavanger fire I remember, one in a hurricane and we had to stop and do some hours for repairs. The other in very calm conditions in bass strait. We pulled a unit on the bass strait one but that did not solve the problem. We spent time going to Sydney, with one unit off fuel, we know the main problem. In both fires we pulled the liners. Both were very worn and due to be lifted, the fires arrived first.
Jim B

makko
21st August 2009, 15:26
Two scavanger fire I remember, one in a hurricane and we had to stop and do some hours for repairs. The other in very calm conditions in bass strait. We pulled a unit on the bass strait one but that did not solve the problem. We spent time going to Sydney, with one unit off fuel, we know the main problem. In both fires we pulled the liners. Both were very worn and due to be lifted, the fires arrived first.
Jim B

Hi jim,
Excessive blow-by into the scavenge space. Very quickly a scavenge fire will occur! A classic EK oral question.
Rgds.
Dave

TIM HUDSON
21st August 2009, 15:42
Doxfords with centre scavenge pump were very liable to scavenge fires especially iwo end cylinders. But the worst I ever encountered was the H & W Opposed Piston Engine. As you say, good control of liners/rings and particularily injectors kept the problem at bay.
tim