Engine Room Air Pressure, Ventilation, and Engine Performance

[dtfeld]

One thing to keep in mind when looking at EGT in marine diesel engines is that the EGT will rise with RPM to a certain point, then start to diminish (or at least flatten out). Then turbo's get spun up and producing more boost air which helps cool things down slightly. Beyond a certain RPM, EGT will start to rise again all the way up to WOT and MAX EGT.

I have a full Maretron EGT setup on my 3126's and it tends to be very sensitive to changes in load (whether it be a dirty bottom or a lot of fuel and passengers). I didnt notice any change running with the hatch open/closed, so I can only surmise the SR engineers di the right calculations.

Changing over to better (and quieter) blowers I think has some merit and benefits both for air flow and cooling.

 

[dtfeld]

On a turbo diesel engine, the correct sensor is a Boost sensor as these are at least in the case of CAT running about 24-28 psi. I guess you could use a MAP sensor, but a regular 0-30 PSI sensor works quite well.

 

[ttmott]

One thing to keep in mind when looking at EGT in marine diesel engines is that the EGT will rise with RPM to a certain point, then start to diminish (or at least flatten out). Then turbo's get spun up and producing more boost air which helps cool things down slightly. Beyond a certain RPM, EGT will start to rise again all the way up to WOT and MAX EGT.

I have a full Maretron EGT setup on my 3126's and it tends to be very sensitive to changes in load (whether it be a dirty bottom or a lot of fuel and passengers). I didnt notice any change running with the hatch open/closed, so I can only surmise the SR engineers di the right calculations.

Changing over to better (and quieter) blowers I think has some merit and benefits both for air flow and cooling.

On a turbo diesel engine, the correct sensor is a Boost sensor as these are at least in the case of CAT running about 24-28 psi. I guess you could use a MAP sensor, but a regular 0-30 PSI sensor works quite well.

The engine room blowers on the Sea Ray boats pull air out of the boat which is what is needed in our boats. For gasoline pulling air out is mandatory. For Diesel pulling air out is desired so bilge/diesel fumes and odors are not pushed into the living spaces.
The pressure sensor I'm talking about is for measuring engine room pressure with respect to atmospheric pressure - not boost pressure. A standard non forced induction gasoline engine MAP sensor is 1 Bar or vacuum to 14.7 PSIA. To measure engine room differential pressure we are in the inches of water range.

 

[Nater Potater]

To measure engine room differential pressure we are in the inches of water range.

Did you get a chance to look at that sensor I posted about this morning? I'm going to get a couple for when I start tuning my turbo Mustang to check for pressure drops across different air filters and intercoolers.

 

[ttmott]

Did you get a chance to look at that sensor I posted about this morning? I'm going to get a couple for when I start tuning my turbo Mustang to check for pressure drops across different air filters and intercoolers.

I did and thanks! I'm more bent on the Dwyer instruments due to my long engineering history with that brand of instrumentation and their minimal hysteresis. Dwyer is the standard for HVAC and ECS systems. On my last boat I instrumented the gears for hydraulic pressure and temperature with Dwyer transducers; they were rock solid.
When you instrument for up and down variability, hysteresis is everything; that dead band when a transition from up to down in pressure as an example.

 

[Nater Potater]

I'm more bent on the Dwyer instruments due to my long engineering history with that brand of instrumentation and their minimal hysteresis. Dwyer is the standard for HVAC and ECS systems.

Good point. I have a u-tube water manometer at work coupled to a precision pressure regulator that could be used to verify the repeatability of the cheapo Amazon special. For 80 bucks, I might just take the chance, especially since it'll only be used during verification cycles, and not for long-term readouts. Please keep us updated on your work.

 

[Skybolt]

@ttmott Tom, not sure this is sensitive enough, but this is N2K and is atmosphere sensitive.

https://acrossoceansystems.com/index.php/nmea2000-pressure-sensors/

 

[ttmott]

@ttmott Tom, not sure this is sensitive enough, but this is N2K and is atmosphere sensitive.

https://acrossoceansystems.com/index.php/nmea2000-pressure-sensors/

I don't think so - too big of a range - we will need in the range of 30 inches of water differential which is less than 1 PSI. A differential pressure transducer has two sense ports so it can differentiate between two pressure areas; engine room and outside of the boat. This is the only way we will know if the ER vents are adequate. Remember also that data is acquired in bits so for a 64 bit data stream the range of the transducer is divided by 64, for example. Consequently the greater range the transducer is the less resolution and greater the hysteresis. If you tried to use a 100 psig transducer to measure 0.5 psig and the data system was 64 bit, a bit toggle would be 1.56 PSI - you'd never see that 0.5 resolution. Most of the better DAS are 256 bit systems. So, to get a smooth curve that means anything at all the transducers need to be close to the range being measured.
Plus it will need to integrate with a DAS (Data Recorder) so 4-20ma would have to be the standard.

 

[ttmott]

I don't think so - too big of a range - we will need in the range of 30 inches of water differential which is less than 1 PSI. A differential pressure transducer has two sense ports so it can differentiate between two pressure areas; engine room and outside of the boat. This is the only way we will know if the ER vents are adequate. Remember also that data is acquired in bits so for a 64 bit data stream the range of the transducer is divided by 64, for example. Consequently the greater range the transducer is the less resolution and greater the hysteresis. If you tried to use a 100 psig transducer to measure 0.5 psig and the data system was 64 bit, a bit toggle would be 1.56 PSI - you'd never see that 0.5 resolution. Most of the better DAS are 256 bit systems. So, to get a smooth curve that means anything at all the transducers need to be close to the range being measured.
Plus it will need to integrate with a DAS (Data Recorder) so 4-20ma would have to be the standard.

To add, on some of your Maretron data being displayed you will see a stair-step in the graph function - that is the bit toggle.

 

[Flyer5]

A nice simple gauge something like this would even work. I would assume you really don't want to see any negative or any positive.
https://www.amazon.com/Dwyer-Magneh...mzn1.fos.18ed3cb5-28d5-4975-8bc7-93deae8f9840

 

[Skybolt]

I don't think so - too big of a range - we will need in the range of 30 inches of water differential which is less than 1 PSI. A differential pressure transducer has two sense ports so it can differentiate between two pressure areas; engine room and outside of the boat. This is the only way we will know if the ER vents are adequate. Remember also that data is acquired in bits so for a 64 bit data stream the range of the transducer is divided by 64, for example. Consequently the greater range the transducer is the less resolution and greater the hysteresis. If you tried to use a 100 psig transducer to measure 0.5 psig and the data system was 64 bit, a bit toggle would be 1.56 PSI - you'd never see that 0.5 resolution. Most of the better DAS are 256 bit systems. So, to get a smooth curve that means anything at all the transducers need to be close to the range being measured.
Plus it will need to integrate with a DAS (Data Recorder) so 4-20ma would have to be the standard.

So your not looking to just compare the ER pressure to atmosphere? You want to compare the outside fluctuation to the ER pressure?

I guess it comes down to what the resolution is of the A2D your using. 256 bit is going to cost a bit to get that setup. I guess you could do it with an Arduino and a pressure transducer running someones test program.

This could probably do the conversions needed, depending on the transducer requirements and a good start, very simple.
https://learn.sparkfun.com/tutorials/analog-to-digital-conversion/all

 

[ttmott]

So your not looking to just compare the ER pressure to atmosphere? You want to compare the outside fluctuation to the ER pressure?

I guess it comes down to what the resolution is of the A2D your using. 256 bit is going to cost a bit to get that setup. I guess you could do it with an Arduino and a pressure transducer running someones test program.

This could probably do the conversions needed, depending on the transducer requirements and a good start, very simple.
https://learn.sparkfun.com/tutorials/analog-to-digital-conversion/all

Actually it comes down to using instrumentation that has range close to the same as actually anticipated and then recording it with reasonable resolution. The instrument can't have a range 5X what is being measured and expect to see good data. The second important data point is temperature as that is directly related to air density. The third data point is engine load as that is the affecting variable source.
With these data overlaid on a graph in reasonable resolution, a solid story can unfold on the performance of the engine room air intakes.

 

[ttmott]

I know a host of NASA test engineers that would wet themselves to take this on for fun. Too bad we can't pull off a "G Job". We engineers, however, tend to succumb to paralysis by analysis. The data will never be good enough....

 

[Skybolt]

Actually it comes down to using instrumentation that has range close to the same as actually anticipated and then recording it with reasonable resolution. The instrument can't have a range 5X what is being measured and expect to see good data. The second important data point is temperature as that is directly related to air density. The third data point is engine load as that is the affecting variable source.
With these data overlaid on a graph in reasonable resolution, a solid story can unfold on the performance of the engine room air intakes.

So if the right transducer is selected then that circuit should work for what your looking for. The Arduino has a pretty wide range of input characteristics and I am sure it would support one of the Dwyer instruments transducers. Also I am sure you have MAP pressure on of of your displays? That could give you exactly what your looking for.

 

[jmauld]

A common automotive MAP sensor would be 0 to 5 Volt output which would work but it's pressure range would be too great to get any data. This Dwyer instrument (https://dwyer-inst.com/products/pre...-616kd-differential-pressure-transmitter.html ) which is inexpensive at 0-25 In WC (0 - 0.90 PSID) differential would work great and it is 4-20 ma output compatible with the Maretron CLM100. We would need to add temperature and engine RPM as that data is also required. This would all be good but it's real time viewing; we need some way to record and overlay the data in a spreadsheet. The data needed is - Engine RPM, Engine Room/atmospheric Differential Pressure, Engine Room Temperature, and outside temperature. Throttle position would also be good as that would tell us the engine's behavior at temperature/pressure changes.

does your maretron put all of that data on the nmea2000 network?
if so:
https://yachtdevicesus.com/collecti.../nmea-2000-router-ydnr-02-w-nmea-0183-seatalk

 

[carterchapman]

Some quick numbers show my QSM11's need 912 Cubic Feet of air per minute at 2300 RPM and 30 psig boost loaded. That is a lot of air flow...

Tom - I seem to remember Gary (@Four Suns) posted about his 480's port engine having a lack of airflow. He could tell a difference with the hatch opened or closed...It was a very old post - maybe 10 years ago...

 

[Skybolt]

does your maretron put all of that data on the nmea2000 network?
if so:
https://yachtdevicesus.com/collecti.../nmea-2000-router-ydnr-02-w-nmea-0183-seatalk

I have that YachtDevices gateway. The Actisense NGT-1 is much better with their free software. The NGT-1 can display PGN's live. Real nice diag tool. They just replease the W2K-1 wifi interface as well. Both will connect to their data reader.

But no the Maretron does not log data. You need to buy their Data Logger which is their computer for N2K View.

 

[Stray Current]

Once I’m done with my drive refinishing and new props and get back in the water I’m definitely sticking a recording manometer in the bilge with the blower, main and genset running

I think I have plenty of flow on my 260

 

[becnme]

I’ll through a little input in here as I have the same questions and have done everything Tony A recommended. I must admit I fail to remember the exact numbers so if someone has the answer feel free to plug it in here.
First off I run the engine room blowers the entire time the engines are running and for an average of thirty minutes after Engine shut down to continue the slow cool down needed IMHO. Cast iron, steel and everything down there does not cool off very well with no air movement so my fans run.

I’ve run GT with the engine hatch wide open to see what if any differences I got with my Digital EGT sensors and find less almost no temp change.

If I recall Cummins correctly states the entering air temperatures should not exceed 30 degrees above ambient air temperature.

For simplicity sake on 90 degree day the EAT should not exceed 120 degrees. In any RPM range 1800+ the turbo has spooled up pretty good and my digital temperature sensor mounted just in front of the turbo intake filters show I’m within the 30 degree delta.

Most of my running is around the Chesapeake Bay Area except when we head south in November. I often wondered what the TD was for boats running in the Florida area during the summers with high ambient weather temperature conditions. I find the highest EGT readings I ever have are when you start running anywhere below 1800 RPMS and they become grossly worse if you’re running pretty much anywhere below there because of rough sea conditions.
The 30 TD between ODT & entering intake air temperature number is what I remember from a Cummins document I’ve seen & read somewhere but memory fails exactly where I read that. As the sea water gets hotter the Higher RPMs I tend to run to keep the EGT <1,000.

The intake air temp sensor installed in the intake manifold is an indication of your aftercooler condition. It cools the intake air that has run through the the aftercooler post turbo which is much hotter than engine room temp.
I live and boat in Florida and on my last 2 Cummins powered boats after I did the aftercoolers and props per SBMAR even on the hottest day in August the intake air temp was never above 95 with EGT
temps 700-800. Well performing after coolers will cool the intake air to within 10-12 deg of sea temp.
This allows the computer to let the engines perform better as ttmott mentions in a later post.
These engines were QSC's and maybe QSM11's have higher values.

 

[ttmott]

Tom - I seem to remember Gary (@Four Suns) posted about his 480's port engine having a lack of airflow. He could tell a difference with the hatch opened or closed...It was a very old post - maybe 10 years ago...

Yes, and I've heard this from several sources then reading the article in PMY this month. But, to my knowledge I know of no one that has instrumented the boat and collected hard data - not even PMY....
Now knowing how Sea Ray designs boats I'm sure they instrumented their test boats to ensure the minimum requirements from the engine manufacturers are met. But, then again, they really missed the mark on propeller sizing in quite a few of our boats.

I've been perusing Ebay, Bring a Trailer, Race Junk, FaceBook, etc for a DAS to get this kicked off but there is little out there until you get into the several Boat Buck territory. I want to collect data points and load an Excel file....