Jump to content

Improving airflow to engine


blackrose

Featured Posts

8 minutes ago, blackrose said:

I'm going to install a bilge blower next to one of my 2 engine room vents to improve cool airflow to the engine. 

For what purpose? 

My engine room blower in my lumpy water boat  is an extract to remove fumes  from the engine bay.  To be honest I never use it. 

Some boats have these automatically on when the engine is running but really they should run on for say 15 mins after the engine is stopped .

 

 

 

Link to comment
Share on other sites

12 minutes ago, MartynG said:

For what purpose? 

 

 

To improve cool airflow to the engine.

 

19 minutes ago, Loddon said:

My snail blower sucks hot air from just above the alternator up and out of the roof.

Works well since I removed the thermostat😎

 

So I should install it to blow the hot air out?

 

I think that would probably also have the benefit of fewer leaves, insects and debris being sucked in.

Edited by blackrose
Link to comment
Share on other sites

6 minutes ago, blackrose said:

 

To improve cool airflow to the engine.

 

 

So I should install it to blow the hot air out?

 

I think that would probably also have the benefit of fewer leaves, insects and debris being sucked in.

Logic tells me that you have it set up to suck cool air in which you can direct via ducting to the parts of the engine compartment you want cooled. If it were set up to suck air out it would take air from the whole compartment. Were you wanting it to remove fumes suck out would be best. My views.

Link to comment
Share on other sites

23 minutes ago, MartynG said:

My engine room blower in my lumpy water boat  is an extract to remove fumes  from the engine bay.  To be honest I never use it. 

You would use it if you had a boat with a petrol engine 😱

Mine removes hot air from above the engine which is replaced by cooler air from the bilges. 

Diesels like cooler air.

Link to comment
Share on other sites

12 minutes ago, Jen-in-Wellies said:

What leads you to believe the engine room needs more cool air? Is any particular component showing signs of overheating? What signs?

 

No signs of anything overheating. But in summer it gets very hot down there and as we all (should) know, diesel engines like cool air 

 

6 minutes ago, Paringa said:

Beat me to it...

 

Really they are used to extract fumes, but if you want to give yourself a job, feel free. Use as extractors not blowers if you do go ahead.

 

Yes I know what bilge blowers are primarily used for, but as I said in my original post, I'm using one for a different purpose.

Edited by blackrose
Link to comment
Share on other sites

14 minutes ago, Slim said:

Logic tells me that you have it set up to suck cool air in which you can direct via ducting to the parts of the engine compartment you want cooled. 

 

I want cooler air to the air intake. I thought about ducting to the air intake but decided that wasn't a good idea in case a wave hit the vent and the water went straight into the engine!

 

Blowing the hot air out or sucking cooler air into the engine room is a compromise.

Link to comment
Share on other sites

6 minutes ago, blackrose said:

No signs of anything overheating. But in summer it gets very hot down there and as we all (should) know, diesel engines like cool air 

 

You don't necessarily need a blower for this, some ducting throwing outside air towards your alternator(s) and your engine intake should be enough.

2 minutes ago, blackrose said:

 

I want cooler air to the air intake. I thought about ducting to the air intake but decided that wasn't a good idea in case a wave hit the vent and the water went straight into the engine!

 

Blowing the hot air out or sucking cooler air into the engine room is a compromise.

 

Hah bad timing on my post.

 

The ducting doesn't have to attach directly to the intake, just needs to have a cooler airflow near it.

Link to comment
Share on other sites

2 minutes ago, blackrose said:

 

No signs of anything overheating. But in summer it gets very hot down there and as we all (should) know, diesel engines like cool air 

A 2l diesel engine will be trying to breath around 25l a second at 1500rpm, which is a lot, so any fan would need to be able to keep pace. If it can't, then you might end up restricting air flow, rather than improving it by putting a fan in one of the room intakes. The engine running on its own will be effectively changing the air in the room at frequent intervals, drawing in fresh from outside. Areas away from the path of the air from the engine room vents to the engine intake may be "dead" air and not get changed so often, heating up, but the main air in to the engine is probably quite cool. Worth sticking a thermocouple in the engine air intake and getting the real temperature? Ducting air direct to the engine intake could mean that everywhere else heats up as it isn't getting changed with fresh so often, possibly overheating alternators? Real measurements needed again.

  • Greenie 2
Link to comment
Share on other sites

Blowing colder air in is more efficient than removing hot because the cooler air is more dense  (that is why your diesel likes it) so you get a greater mass in for the same volumetric flow rate.

 

If you do blow air  in you need to make sure the air is going where if will do some good.  It is just wasted fuel/electric if the air immediately escapes  through gaps and vents.  

 

N

Link to comment
Share on other sites

Diesel engines run at lower revs by restricting the fuel flow, not the air. The only time having cooler, denser air would lead to more power would be at maximum. The rest of the time, which is 99.99% of running for an inland waterways boat, there will still be enough air to burn the diesel being injected. Air density is important for a petrol racing car engine, but not for this.

  • Greenie 4
Link to comment
Share on other sites

I had a redundant hole after moving the exhaust exit to the opposite side, so instead of blanking it off I fitted a bilge blower fan to suck in cool air and ducting to blow it over the alternator. In hot weather it made the engine bay about 10 degrees cooler, and hopefully will considerably prolong the life of the alternator. Putting a hand near the bay's original vent also showed that the fan provided enough air for the engine at up to 2000 rpm, above which speed it started to suck more through the vent.

  • Greenie 1
Link to comment
Share on other sites

1 hour ago, BEngo said:

Blowing colder air in is more efficient than removing hot because the cooler air is more dense  (that is why your diesel likes it) so you get a greater mass in for the same volumetric flow rate.

 

If you do blow air  in you need to make sure the air is going where if will do some good.  It is just wasted fuel/electric if the air immediately escapes  through gaps and vents.  

 

N

 

To an earlier point about the fan restricting airflow. It won't cover the entire vent and it could be located slightly away from the vent.

 

Good point about cooler air being denser so sucking air in being more efficient. The only gaps in the engine space are the vents themselves and I can't see there's going to be much wasted energy. The 12v fan draws a few amps and it would only be on when the engine is running.

1 hour ago, Jen-in-Wellies said:

Diesel engines run at lower revs by restricting the fuel flow, not the air. The only time having cooler, denser air would lead to more power would be at maximum. The rest of the time, which is 99.99% of running for an inland waterways boat, there will still be enough air to burn the diesel being injected. Air density is important for a petrol racing car engine, but not for this.

 

So how do you account for Julian's (Loddon's) reported benefits?

1 hour ago, Keeping Up said:

I had a redundant hole after moving the exhaust exit to the opposite side, so instead of blanking it off I fitted a bilge blower fan to suck in cool air and ducting to blow it over the alternator. In hot weather it made the engine bay about 10 degrees cooler, and hopefully will considerably prolong the life of the alternator. Putting a hand near the bay's original vent also showed that the fan provided enough air for the engine at up to 2000 rpm, above which speed it started to suck more through the vent.

 

Ok thanks, again practical experience contradicting what some are saying.

Link to comment
Share on other sites

1 hour ago, Tonka said:

If you had of built a traditional narrowboat you could just open both sets of doors and the piegon box. Sorted

 

That's for that suggestion but I think rebuilding the whole boat is likely to be much more work than simply installing a fan.

 

And on the other hand if you had built a modern narrowboat you'd have a bulkhead between the cabin and engine room to prevent the boat sinking in the event of stern gland failure, etc. Swings and roundabouts...

Link to comment
Share on other sites

I;d want to do some experiments first. Maybe put a polythene, sheet over the engine hole, place a smoke pellet by an engine intake and see what the air flow inside the engine compartment actually does before putting in a fan. If the air moves pretty directly from the room vents to the engine air intake, with some going to the alternator,(s), then away via their fans, then I'd be pretty happy with the existing arrangement. If not, then a fan might make a difference.

Link to comment
Share on other sites

4 minutes ago, Jen-in-Wellies said:

Link? Don't recall seeing that.

 

Post 2 and 6 in this thread.

1 minute ago, Jen-in-Wellies said:

I;d want to do some experiments first. Maybe put a polythene, sheet over the engine hole, place a smoke pellet by an engine intake and see what the air flow inside the engine compartment actually does before putting in a fan. If the air moves pretty directly from the room vents to the engine air intake, with some going to the alternator,(s), then away via their fans, then I'd be pretty happy with the existing arrangement. If not, then a fan might make a difference.

 

The experiment will be installing the blower which I've had in my boxes of bits for years. It's really not that much work.

Link to comment
Share on other sites

1 minute ago, blackrose said:

 

Post 2 and 6 in this thread.

Thanks. Thought it was a specific thread, not these replies. Looks like he was trying to solve a specific problem with a hot and bothered alternator, which doesn't sound like what you are trying to do, if you don't have alternators overheating.

Link to comment
Share on other sites

5 minutes ago, Jen-in-Wellies said:

Thanks. Thought it was a specific thread, not these replies. Looks like he was trying to solve a specific problem with a hot and bothered alternator, which doesn't sound like what you are trying to do, if you don't have alternators overheating.

Not trying to solve a problem, my alternators don't get hot and bothered,  it was already fitted when I bought the boat I just removed the thermostat.

The extractor drops the engine bay temperature by about 7deg after a days cruising as measured by the battery temp sensors.

  • Greenie 1
Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.