Csail
N/A
Had a thought that my 37hp inbd. diesel can't really breath.It works fine but the engine room is fairly well sealed.How big a vent hole should i make?
Intake air
- Thread starter Csail
- Start date
boatmike
Well-Known Member
Chandlers usually stock small stainless steel grilles, some round, some square. the smallest of these would suffice as the theoretical answer to your question is no more than the diameter of the intake to the engine which is usually no more than 1.5 inches on an engine of this size.
BAtoo
Well-Known Member
Our 28HP is in a fairly spacious "engine room" and has two 100mm/4" flexible tubes running from s/s inlets on the transom and has two more s/s inlets feeding down from the outside by the hatch plus the odd "leak" around cables etc- so a little more than csail's 1.5"hole .........
duncanmack
Well-Known Member
Whilst that is "theoretically" correct, in practise fit a much bigger one (or put a fine mesh over the little one) unless you want your engine room full of flies, seagulls, passing pwc's - OK a little exaggeration, but your engine will be sucking in about 30 litres/second of air. Bit like a good hoover.
/forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif
/forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif
oldsaltoz
Well-Known Member
G'day Csail,
Both our engine rooms are self contained to reduce noise and smell, both have a 12 inch flexible hose that runs from the upper deck via a vent facing aft to the lowest part of the engine room, Keeps everything nice and cool.
We also have two small vents at the top of the engine room to let any hot air out, (Cold into the bottom = hot out the top). I was considering installing a small extractor fan on a pulley but after running the above it was not required.
Hope this heps.
Avagoodweekend......
Hope this helps
Both our engine rooms are self contained to reduce noise and smell, both have a 12 inch flexible hose that runs from the upper deck via a vent facing aft to the lowest part of the engine room, Keeps everything nice and cool.
We also have two small vents at the top of the engine room to let any hot air out, (Cold into the bottom = hot out the top). I was considering installing a small extractor fan on a pulley but after running the above it was not required.
Hope this heps.
Avagoodweekend......
Hope this helps
boatmike
Well-Known Member
I agree that is true and the smaller the hole the greater the velocity. A bigger vent will reduce the crap that gets sucked in. It will however also cause noise to be transmitted through the hole and it is surprising how vents transmit noise. Also it can create a downflooding problem if sited poorly.
I was keeping it simple. A small ( say 4") stainless steel louvre vent will do the job and keep most rubbish out. If you can, mount it as high as possible so that with a flooded cockpit you wont drown your engine. It can of course be in the cabin rather than outside. Depends entirely on the type of boat, location of engine,and how much you care about soundproofing. As I said, theoretically it need not be very big to do the job of allowing the engine to aspirate.
I was keeping it simple. A small ( say 4") stainless steel louvre vent will do the job and keep most rubbish out. If you can, mount it as high as possible so that with a flooded cockpit you wont drown your engine. It can of course be in the cabin rather than outside. Depends entirely on the type of boat, location of engine,and how much you care about soundproofing. As I said, theoretically it need not be very big to do the job of allowing the engine to aspirate.
TiggerToo
Well-Known Member
Have a look at the air intake here!
http://www.ybw.com/forums/showflat.php/Cat/0/Number/1096750/an/0/page/0#1096750
/forums/images/graemlins/grin.gif
http://www.ybw.com/forums/showflat.php/Cat/0/Number/1096750/an/0/page/0#1096750
/forums/images/graemlins/grin.gif
Rick
Well-Known Member
Rule of thumb for a healthy diesel - clean fuel oil, clean lube oil, and lots of clean air. My Kubota D850 (22hp) struggles with 2 x 4" vents to a well sealed engine box - it's about to get double in an attempt to help it cool.
G
Guest
Guest
TRhe amount of air used by an engine is amazing .... and you also have to note that even with water cooled - you still need a flow of reasonable cool air over the engine.
A ship I sailed on .... Stena Seatrader .... a Roll-on Roll-off ship out of Miami / Ft. Lauderdale was originally built for North Sea / Europe trade ... In the Carib - the engine's couldn't be run full speed as air volume in the engine rooms was insufficient ... that meant for air intake with fuel AND the cooling air around engine.
If the ship returned to N. Sea work - they reckoned she could run full speed.
Just an extreme example ... It is not only air burnt with fuel ... it's far more than that.
A ship I sailed on .... Stena Seatrader .... a Roll-on Roll-off ship out of Miami / Ft. Lauderdale was originally built for North Sea / Europe trade ... In the Carib - the engine's couldn't be run full speed as air volume in the engine rooms was insufficient ... that meant for air intake with fuel AND the cooling air around engine.
If the ship returned to N. Sea work - they reckoned she could run full speed.
Just an extreme example ... It is not only air burnt with fuel ... it's far more than that.
cliff
Well-Known Member
While my DV24 Bukh seems to run fine in its closed engine bay, I usually lift the companionway lid/step about two inches to allow better ventilation. Saves th eproblems of water/fly/seagull ingress.
--------------------
"Artificial intelligence is no match for natural stupidity"
sailroom <span style="color:red">The place to auction your previously loved boatie bits</span>
--------------------
sailroom <span style="color:red">The place to auction your previously loved boatie bits</span>
andy_wilson
Well-Known Member
What makes you think that?
With a clean air filter are you emiting black smoke when running at maximum recommended revs? That would be the only reason to believe you need more air supply, and then only if you are sure you have no exhaust constrictions.
If you show a bit of black smoke at full throttle whilst accelerating, that's normal, The fuel rack is wide open but the pistons aren't pumping enough air to burn it all until they reach full revs.
In my experience most marine aux. engines can get an almost limitless supply of cool air from the bilges, tank spaces, cockpit lockers and whatever they lie adjacent to, most of which are open to fre air in varying degrees.
If you are still needing air, a good solution for sound control is to run a duct continuously from a baffled inlet to a few inches away from the air filter intake. In terms of diameter, the intake diameter gives you a clue. I suppose you could go double, or maybe treble diameter if it is a long run.
Tip 1. If you have a choice, have the inlet pointing down so it draws denser, cooler air from below, rather than hotter air from above.
Tip 2. The engine surface is probably emitting less heat per unit area than a hard working alternator. If you have a need for a high output charging system, there is an argument for ducting cool air to, and pumping the hot air from the alternator area, to save it going into the engine and reducing efficiency.
With a clean air filter are you emiting black smoke when running at maximum recommended revs? That would be the only reason to believe you need more air supply, and then only if you are sure you have no exhaust constrictions.
If you show a bit of black smoke at full throttle whilst accelerating, that's normal, The fuel rack is wide open but the pistons aren't pumping enough air to burn it all until they reach full revs.
In my experience most marine aux. engines can get an almost limitless supply of cool air from the bilges, tank spaces, cockpit lockers and whatever they lie adjacent to, most of which are open to fre air in varying degrees.
If you are still needing air, a good solution for sound control is to run a duct continuously from a baffled inlet to a few inches away from the air filter intake. In terms of diameter, the intake diameter gives you a clue. I suppose you could go double, or maybe treble diameter if it is a long run.
Tip 1. If you have a choice, have the inlet pointing down so it draws denser, cooler air from below, rather than hotter air from above.
Tip 2. The engine surface is probably emitting less heat per unit area than a hard working alternator. If you have a need for a high output charging system, there is an argument for ducting cool air to, and pumping the hot air from the alternator area, to save it going into the engine and reducing efficiency.
oldharry
Well-Known Member
Re: What makes you think that?
Inlet air temperature is important too. An enclosed engine room with only a small vent can build up a fair bit of heat. Not a problem for the engine itself, although not desireable, but the temperature of the induction air directly affects the power output The warmer the air the less oxygen the engine is getting, so the less power it can develop at full throttle.
This is why many diesels, particularly turbos which also heat the inlet air by compression, are fitted with intercoolers, to reduce the air temprature and make it more dense, so the engine gets more oxygen and produces more power. My 90hp TD Peugeot engine loses a rated 4hp at full throttle if the intercooler is bypassed. More important for Mobo types than the average small yacht auxiliary, but the principle remains.
Inlet air temperature is important too. An enclosed engine room with only a small vent can build up a fair bit of heat. Not a problem for the engine itself, although not desireable, but the temperature of the induction air directly affects the power output The warmer the air the less oxygen the engine is getting, so the less power it can develop at full throttle.
This is why many diesels, particularly turbos which also heat the inlet air by compression, are fitted with intercoolers, to reduce the air temprature and make it more dense, so the engine gets more oxygen and produces more power. My 90hp TD Peugeot engine loses a rated 4hp at full throttle if the intercooler is bypassed. More important for Mobo types than the average small yacht auxiliary, but the principle remains.
G
Guest
Guest
Re: What makes you think that?
The intercooler also increases the denseness of the diesel spray due to temp. of air mix .... concentrating more diesel ..... given the denser air - you retain burn ratios ..........
Basically - not one without other !! Air denisty will not give extra HP ....
/forums/images/graemlins/tongue.gif
The intercooler also increases the denseness of the diesel spray due to temp. of air mix .... concentrating more diesel ..... given the denser air - you retain burn ratios ..........
Basically - not one without other !! Air denisty will not give extra HP ....
/forums/images/graemlins/tongue.gif
oldharry
Well-Known Member
Re: What makes you think that?
'S right - everything cooled down means more fuel and oxygen per CC of the inlet charges. Hot engine spaces mean less power.
'S right - everything cooled down means more fuel and oxygen per CC of the inlet charges. Hot engine spaces mean less power.