jackhild59

iTrader: (7)

Just to clarify, a converter doesn't burn anything. Our pollutants react on the surface of a catalyst. Catalytic agents are used so the reaction takes place at a far cooler temperature than that reaction would take place in the natural state(burning).

The converter has two catalyst bricks, one in the front half and one in the back half. The air tube injects air evenly distributed into the open space between.

The engine produces the following pollutants that the catalytic converter treats:

Nitrates/nitrites of oxygen-NOx,
Unburned hydrocarbons-HC
Carbon Monoxide-CO

The front brick contains rhodium. This is the reduction catalyst. It converts nitrates of oxygen into pure Nitrogen and pure Oxygen.

2NOx → N2 +O2

In chemistry, this is called a reduction reaction, because it reduces or removes one or more oxygen atom from the compound (simplified!)

The back brick contains Palladium. This is the oxidation catalyst. It converts unburned Hydrocarbons and Carbon monoxide into Carbon dioxide and Water as follows:

2CxHy + (x+y)O2 → 2xCO2 + yH2O
2CO + O2 → 2CO2

This is called a oxidation reaction because it adds one or more Oxygen atom to the compound(s). (again, simplified)

Platinum may or may not be added to both oxidation and reduction bricks to enhance/tweak the reaction.

Where does the back brick get the extra Oxygen for the back brick to use? 2 places. Under some conditions, the front brick combines enough free O2 to sufficiently oxidize the unburnt HC and the CO. Under other conditions, the oxygen combined in the front brick is insufficient, so the air is pumped into the converter via the air tube in the middle. The engineers can sufficiently predict the engine states so as to provide controls to apply the correct amount of air into the correct place in the system, based on the rpm, engine load, throttle position etc. This is the control system that Hailers describes so nicely.

By their nature, rotaries are not terrible NOx offenders, as AGreen says.

Once we got piston engines to OBDII, most cars dropped the air tube to the 3-way converter. They get by just fine with a 3-way and no air tube. The relatively clean burning piston engine produces enough NOx in the front brick to provide sufficient free O2 to oxidize the (relatively low) unburned HC's in the back brick.

If you do not believe my explanation, look it up.

Class dismissed.

Richter12x2

iTrader: (1)

I did notice that some catalytic converters are convertible types, but if you run it without the air pipe, you install it reversed and seal the airpipe port. I presume this is so whichever of the two bricks gets more o2.

jackhild59

iTrader: (7)

The convertible style catalytic converter is intended to reduce SKU's for the manufacturer and the distribution channel. IOW one unit can fit more types of cars.

I don't understand why they would reverse it; there may be some advantage to this that some engine manufacturers utilize. Low emission and ultra low emission technology is advancing at a rapid pace.

The aftermarket high capacity converter I use on my N/A vert was rated to be used with or without an air pump attached. There was a cap that you left on if you did not hook up an air supply, but I do not remember anything being said about reversing it. I just hooked up the air-pipe and followed the flow arrow.

Richter12x2

iTrader: (1)

It may not be for all - but I remember installing a cat that had arrows on each end - it pointed one way for No Air Pump and the other way for Air Pump - the No Air pump direction pointed the air pump tube away from the engine bay. Maybe there's another reason for doing this, but it would definitely reverse the order of the catalysts

HAILERS

Here's a jpg of a catalytic converter and the arrow mentioned.

Another jpg of a ACV with two pieces of vacuum hose conneted to the two holes on it that come from the Relief and Switching solenoids. Plus a MITTYVAC . Connect the Mittyvac to a hose and apply vacuum and then you can blow thru the airpump inlet hose and see where the air goes in a given situation. The jpg and Mitty are not that clear but a person could get my drift by using Imagination.

JUST FYI: Earlier when I was describing the actions of the ACV and the LEDS, I was referring to the NON TURBO ACV. The TURBO ACV is a little different in that it uses air PRESSURE to open the Relief diaphram plus other minor differences.

Juiceh

iTrader: (4)

Thats pretty much what I did. I used a cheapo $65 2.5 inch "hiflow" autozone cat with and airpump connection. I had it custom flanged into my exhaust system to replace my REV TII RB presilencer. Then I had it hooked up to an LS1 airpump that was controlled by a switch in the cabin. I passed with flying colors with a totally screwed up over rich tune.
https://www.rx7club.com/2nd-generation-specific-1986-1992-17/%2Aupdate%2A-street-ported-tii-swapped-vert-il-smog-resluts-%2Apics%2A-515579/

Nick86

iTrader: (1)

This is a very interesting discussion about emissions, catalytics and rotary specific emissions equipment.

It's worth keeping in mind that in the results posted at the beginning of the thread, the car does not have an EGR, nor an ACV. The air pump draws air through a cheap bolt-on filter and dumps it straight into the split air pipe and into the main cat.

It would be interesting to test the effect a functioning ACV and EGR would have on my car if I tested it again..... but that wont happen! lol

HAILERS

It's also very interesting that you did PASS the rolling part of the test on your FIRST try but not the IDLE part of the test. Which means to me the catalytic converter did NOT need AIR from any airpump to pass the rolling test. But at the IDLE test it's very much NEEDED. I'm done with this trhread.

Richter12x2

iTrader: (1)

Awesome, I knew I wasn't dreaming it - my dreams are a lot weirder than arrows on catalytic converters.