Perkins air intake noise trials

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pcatterall

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So I carried the massive ford ranger air filter assembly to Sardinia for trials.
The results were not impressive and are here as recorded on my decible app

Revs. Without filter. With filter
750. 56. 60
1000. 58. 61
1500. 68. 71
1800. 69. 70
2000. 68. 66
2500. 76. 65

Our cruising revs are 1800 .
We did feel that even at the lower revs the sound quality with the filter on was better ( softer) but the filter would have been difficult to mount in the engine space so we decided not to bother. If we commonly worked in the higher rev range then the difference in actual noise and the quality of the noise would have made fitting (somehow) more worthwhile.
 
A very interesting set of results. My guess is that the air filter is to big for the size of the engine. Hope someone has experience of this (and can do the maths!) but to me it would appear that the noise is reducing when the filter assembly starts to become slightly restrictive as the RPM rises? Would make sense if we assume that this is working like an exhaust silencer in reverse?
A lot of effort to get a disappointing result for you but a good result for moving the problem forward.

Thinking on the problem there could be a resonant (anti?) effect at 2-2.5K as the reduction is dramatic here. If this were an exhaust I would suggest that the tuned length is in here somewhere. Any mathematicians around? not had my coffee yet?
 
If you look at the basic physics then:

sound velocity = frequency x wavelength

The speed of sound is nominally 330m/sec, assuming the air isn't compressed ie non turbo.

4 cylinder engine, 4 stroke, the valves open twice per rev.

If you are looking for an antiphase reflection from either an open or a stopped pipe, then the pipe needs to be a quarter wave long.

this gives some approximate lengths of:

[TABLE="width: 512"]
[TR]
[TD]Cylinders

[/TD]
[TD][/TD]
[TD="align: right"]4[/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[/TR]
[TR]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[/TR]
[TR]
[TD="colspan: 2"]speed of sound [/TD]
[TD="align: right"]330[/TD]
[TD]m/sec[/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[/TR]
[TR]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[/TR]
[TR]
[TD]rpm[/TD]
[TD][/TD]
[TD]Hz[/TD]
[TD][/TD]
[TD="colspan: 2"]Wave length (m)[/TD]
[TD="colspan: 2"]1/4 wave length (m)[/TD]
[/TR]
[TR]
[TD="align: right"]1000[/TD]
[TD][/TD]
[TD="align: right"]33.33[/TD]
[TD][/TD]
[TD="align: right"]9.90[/TD]
[TD][/TD]
[TD="align: right"]2.48[/TD]
[TD][/TD]
[/TR]
[TR]
[TD="align: right"]1500[/TD]
[TD][/TD]
[TD="align: right"]50.00[/TD]
[TD][/TD]
[TD="align: right"]6.60[/TD]
[TD][/TD]
[TD="align: right"]1.65[/TD]
[TD][/TD]
[/TR]
[TR]
[TD="align: right"]1800[/TD]
[TD][/TD]
[TD="align: right"]60.00[/TD]
[TD][/TD]
[TD="align: right"]5.50[/TD]
[TD][/TD]
[TD="align: right"]1.38[/TD]
[TD][/TD]
[/TR]
[TR]
[TD="align: right"]2000[/TD]
[TD][/TD]
[TD="align: right"]66.67[/TD]
[TD][/TD]
[TD="align: right"]4.95[/TD]
[TD][/TD]
[TD="align: right"]1.24[/TD]
[TD][/TD]
[/TR]
[TR]
[TD="align: right"]2500[/TD]
[TD][/TD]
[TD="align: right"]83.33[/TD]
[TD][/TD]
[TD="align: right"]3.96[/TD]
[TD][/TD]
[TD="align: right"]0.99[/TD]
[TD][/TD]
[/TR]
[/TABLE]

These lengths look too long to be practical in a typical engine room, although they will be shorter than that in practice because the air has a velocity as it comes into the inlet manifold.

So, I guess any silencer on the induction side has to be a labyrinth design, i.e. to put as many absorbent surfaces, arranged so that the sound is reflected off them before it reaches the outside world, without seriously compromising the flow of air into the engine.

I've spent some time hassling this problem and bought a Ford Ranger air filter to try on my Yanmar 4JH4E, but it's too big to fit in the engine bay, so I'm considering making a filter based on a labyrinth design out of sheet alloy and fire retardant sound absorbing foam, as used in cars, under the bonnet and places like that.

I'd really hoped I could find a readily adaptable air filter which would be effective and the Ford Ranger looked promising, the engine is 2.5L and the rev range similar, but a bit higher than a typical marine engine, but I guessed a Ranger would spend a lot of time cruising at 1800 to 2000 rpm.

Many moons ago, I spent a lot of time tuning car engines, building tuned exhaust systems, polishing cylinder heads and manifolds and fettling twin choke Webers. I'll have to see how much of that I can remember, although at the time I wasn't interested in noise reduction, just more power!
 
That's interesting and useful Ian.
The hose length on my experiment was quite short so the benifts by your kind calculation would be apparent at the higher revs and this is borne out in practice.
I recently posted about trials with Eberspachers air intake hose where positive noise reduction was obtained by simply using a longer intake hose.
The noise was reduced but mostly measured around the mouth of the intake pipe.
On the boat I will experiment some more using different lengths of hose but nearer your quoted optimum for my normal rev range.
I have plenty of room for hose and perhaps routing it so the mouth is somewhere where the noise is deadened may help.
Thanks again for the good steer!
 
You need to be aware that the calculations are based on the sound generated by the inlet valves opening. The lengths will vary with the number of cylinders and won't work for a diesel heater, which produces a wide range of frequencies from the continuous combustion.

It may be worth looking up the sound absorber called a Rayleigh Horn on Google. The basic idea is that sound gets reflected many times and each time it's reflected it looses a bit of energy, the horn is shaped so the sound can't escape. A long pipe with bends in it will act a bit like a Rayleigh Horn and can be quite a good sound absorber.
 
Hi Ian
A very useful analysis.
As a matter of interest, as far as I am aware the Perkins engines were the marinized version of the B. Leyland 2 litres engines which were used in their van and Volvo had taken them over from Perkins. Are there no Volvo air intake filters off the shelf?? and would it not a better soundproofing of the engine compartment improve the noise levels??
 
I guess that there may well be off the shelf filters but their value as mufflers may be questionable. My new expert (Ian ) demonstrates that the hose length may be critical in optimising noise reduction at the critical engine speeds.
On a boat this would seem to be at normal cruising speed, in a vehicle there will be a need to consider a range of engine revs.
My own failed test suggested that there would be serious reductions in noise if my cruising revs were 2500 rather than the required 1800.
Quite rightly there is a need to look at sound proofing as well. In my own case I have applied it where I reasonably can, I can do more but it has got complicated now and there seem better prospects in pursuing the intake noise route next.
 
I have had success in the past with an air filter from a series III landrover - oil bath, centrifugal, oiled steel mesh and a hose about 18" long.
 
I think you are on to something re length of induction hose being more important than actual filter.
Has to do with wavelength,standing waves,etc.
The auto & bike racing fraternity learned this many years ago re exhaust scavenging.
My own experiment:
I have a VP2003 mounted under pilothouse deck with standard VP 2003 intake filter/horn? as eqpd from factory.
I slid a length of corrugated 1.5" sump pump hose(Like the white bilge pump hose) on over the snout of filter & lead it across under deck & up the space between outer hull & inner p/house "wall"-a total length of 4 1/2 ft across & 4 1/2ft vertical-total approx 9ft of hose. Nothing on the upper end-just placed it near the louvered vent that serves as a fresh air intake for my eberspacher.
The results were an amazing reduction in sound. I did not have a meter to measure,but it was more than worthwhile.

The downside was at about 2000 RPM & up,a horrid moaning sound developed. I am sure it was due to air rushing over the corrugations or some such. There was no problem with engine-same power,no smoke, & normal max revs.

I ended up sliding the hose off the air filter & just leaving it lie close to air filter intake for now.The normal previous engine noise returned.

I will get back to experimenting with different hose this season.Perhaps smooth bore,a bit larger maybe, etc.

Cheers/ Len
 
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