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saunders
saunders

Posted: Mon Jun 01, 2009 6:51am

Post Subject: Engine bay temperature

Dear Tony After sorting out my calorifier connection in a previous question to you, I have now put in a Hospital silencer in the engine bay of my trad narrowboat along with the foil backed insulation panels and blocking of gaps it has made a massive difference to the noise level. My question to you is their is no ventilation to the outside of the boat and from reading on the Bukh (TW Marine) website that engines require a good supply of cool clean air. On the flip side of this the Bukh engine if run a bit hotter will burn off the excess fuel and so cut the smoke down which apparently they have. Hopefully you have an idea or a solution because the reason for the Hospital silencer and the foil backed insulation panels were too make a really quite boat, the idea of cutting a hole in the boat seems like a nasty job plus letting the noise out again. Many thanks Steve

Tony-B
Tony-B

Posted: Mon Jun 01, 2009 9:19am

Post Subject: Engine bay temperature

Dear Steve, I fear the "smoke" problem on a DV36 (if that is what you have) is more to do with insufficient swirl in the combustion chambers at low speed giving incomplete combustion. This is a well known characteristic of direct injection engines designed before computer modelling was readily available. Running the any engine with a high ambient engine room temperature is likely to make the smoking worse because the air will expand and thus pass less oxygen into the combustion chamber. It is one of the major causes of excess carbon build up in boat engines, as is restricting the air supply which in turn limits the oxygen available. FWIW I have recently fitted a new prop on my DV36 and the smoke seem to have been reduced. The engine has to rev a bit higher for the same speed so that might explain why. I have also found one of the fuel additives that contain cerium helps. Now back to your problem. You really MUST ensure an adequate air supply and I would not use less than a 3" diameter hole. You will need to make a baffled and soundproof lined "entry box" which I am sure TW Marine show on their website. This will allow air in but absorb any sound trying to come out. I can not advise where to fit it without seeing your boat. If you try to operate the engine in a virtually airtight box you can expect more smoke and also will face repair bills. You also have to consider how a high ambient temperature may effect alternator cooling. Tony Brooks.

saunders
saunders

Posted: Thu Jun 04, 2009 7:16am

Post Subject: Engine bay temperature

Dear Tony so on the smoke thing it used to be a lot worse than now, because the boat had been stood for 3 - 4 years without a service with old fuel and dirty filters. After the service and the new silencer it is 100% better, the point you made about the prop is something too look at, as a fellow boater reckoned the boat seemed under proped, suppose I can't do much about this until it is out of the water?. On the ventilation issue would it be worth trying a 12v ventaxia type fan gadget pulling the hot air out, with some ducting to draw the cool air in and around the air filter and alternator, my idea is to do this in the area around the cockpit, as this is open most of the time while the engine is running.Thanks Steve

Tony-B
Tony-B

Posted: Thu Jun 04, 2009 8:51am

Post Subject: Engine bay temperature

An undersized prop will allow the engine to rev more freely so at any given canal speed the engine revs will be higher than a "correctly" propped boat. This should increase the air speed entering the cylinders and thus increase the amount of air swirl - as will the higher piston speed. It also means you are driving the alternator faster at canal speed and that has advantages as well. If the boat stops well then leave the prop alone. If this is a DV36 my calculations at a canal speed of about 1400rpm show you need a fan rated at 45 cu.m/hour just to supply the combustion air so you need a higher capacity fan than that to actually blow any excess air in. If you are intent on sucking out I think the engine may simply overcome the fan. My view is that if you can supply a suitably sized cool air duct or vent close to the back of the alternator the engine will do the rest by constantly eating the hotter air. It is the lack of or undersized vents that cause the problems. My own DV36 is boxed in by a wooden box with just enough space around it for maintenance access but the area at the back from engine bed level to the base plate is open as an air supply. I do not find any evidence of excess temperature or air starvation. I come back to the baffled intake system as shown on the TW Marine instructions. I also do not think you will stop any DV36 (if that is what it is) smoking a bit on idle and at low speed.

saunders
saunders

Posted: Fri Jun 05, 2009 6:33am

Post Subject: Engine bay temperature

Thanks again Tony. For the next improvement, have you any experience on the Aquadrive system and if it makes a difference. Steve

Tony-B
Tony-B

Posted: Fri Jun 05, 2009 7:08am

Post Subject: Engine bay temperature

If the engine is flexibly mounted I think you will find it makes a big difference to the vibrations through the boat. It will also reduce the wear on the engine mounts and stern gland. If the engine is rigidly mounted its major advantage will be the lack of need to align the engine to the shaft but probably not much else. A word of warning, as you strive to reduce engine noise you normally find that transmission whine and hydrophonic noise become more noticeable and annoying. Tony Brooks

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