​ Lightweight & High‑Temperature Resistant Catalytic Substrates for Aircraft Environmental Control Systems

Most people think catalytic converters are for cars and trucks. But they also show up in places you wouldn't expect – like the environmental control system of an aircraft.

The ECS manages cabin pressure, temperature, and air quality. On some planes, bleed air from the engine passes through a catalytic converter before it reaches the cabin. That converter has to remove ozone, carbon monoxide, and other trace contaminants.

But the ECS lives in a brutal environment. High heat. Tight spaces. And every gram of weight matters.

We've built substrates for a few ECS applications over the years. Here's what we learned about making them light enough and tough enough at the same time.

Why ECS Converters Are Different

A car converter sits under the floor. It can be heavy. It can be bulky. Nobody cares.

An ECS converter is crammed into a compartment with a hundred other components – valves, heat exchangers, ducts. Space is tight. Weight is a constant fight. Every part has to earn its keep.

The temperatures are also higher than most people think. Bleed air from an engine compressor can be 500 to 700 degrees Celsius. The converter has to live in that stream, cycling hot and cold every flight.

And the flow rates are huge. A typical ECS might move hundreds of pounds of air per hour. The substrate can't create much backpressure, or the whole system loses efficiency.

The Weight Problem

Standard automotive substrates use 0.05 mm foil. That's thin, but it still adds up. A typical round car converter weighs maybe 1.5 to 2 kg. For an ECS, that's too heavy.

We've gone as thin as 0.03 mm for one aircraft customer. That's about the thickness of aluminum foil you'd use in the kitchen. It's delicate – you have to handle it with foam gloves. But it cuts weight by almost 40% compared to standard.

The trade‑off is durability. Thin foil dents easily. It can crack under vibration if the mounting mat isn't perfect. So you don't go that thin unless the weight budget is really tight.

For most ECS applications, 0.04 mm is a good middle ground. Lighter than standard, but still robust enough to survive.

The Heat Problem

Aluminum is out. No question. At 500 degrees, aluminum loses half its strength. At 700, it's like butter.

So we use stainless. Usually 304 or 316. Those hold up to about 750 degrees before they start creeping – slowly sagging under their own weight.

But some ECS applications push past 750. That's where you need higher alloys. 347 stainless has better creep resistance. Inconel is even better, but heavy and expensive.

For one ECS customer, we used 347 stainless with 0.04 mm foil. That kept the weight down and the heat tolerance up. They tested it to 800 degrees for short periods. No sagging.

Cell Density for Low Backpressure

ECS converters need to flow a lot of air with very little pressure drop. High cell density is the enemy here.

We typically recommend 200 to 300 cpsi for ECS applications. 200 flows great – almost like an open pipe. 300 still flows well but gives more surface area for the catalyst.

One customer tried 400 cpsi on their own. The backpressure was too high. The ECS couldn't maintain flow at altitude. They dropped to 300 and the problem went away.

So don't assume more cells is better. For high‑flow ECS, less is more.

Brazing for Thermal Cycling

An aircraft flies. It lands. The ECS heats up, then cools down, then heats up again. That thermal cycling is hard on brazed joints.

We use a high‑temperature brazing filler with a melting point well above the operating temperature. For stainless substrates, that's a nickel‑based filler. It doesn't soften at 700 degrees.

We also control the cooling rate after brazing. Slow cooling reduces internal stress. That helps the joints survive hundreds of thermal cycles without cracking.

One of our ECS customers sent us a failed substrate from another supplier. The brazing had micro‑cracks all along the joints. They switched to our process. No more cracks.

Mounting Mat – The Hidden Variable

The mat that holds the substrate in the can is critical – especially when weight is tight.

Standard mats are dense and heavy. For ECS, we use lightweight, high‑temperature mats. They're less dense, but still expand enough to lock the substrate in place.

We also control the gap between the substrate and the can more tightly than for automotive. A smaller gap means a thinner mat can be used. That saves grams.

One customer shaved 80 grams off each converter just by optimizing the mat and gap. That doesn't sound like much. But on an aircraft, 80 grams here, 80 grams there – it adds up.

Testing We Do for ECS Substrates

We don't just make these parts and hope. We put them through tests that would destroy a normal converter.

High‑temp sag test. Heat the substrate to 700 degrees, support it at the ends, put a weight in the middle. Measure how much it sags after 24 hours. Good substrates sag less than 1 mm.

Thermal cycle test. 200 cycles from room temperature to 700 and back. Then measure backpressure and look for cracks.

Vibration test. Mount the substrate in a can, shake it at aircraft‑typical frequencies for 24 hours. Check for loose pieces or fretting.

Flow test at temperature. Measure backpressure at room temperature and again at 600 degrees. The difference should be small. If it's large, the substrate is distorting when hot.

We keep records of all these tests. If a customer asks, we can show them the data.

Real Numbers from a Past Job

We made a batch of ECS substrates for a regional jet manufacturer. Specs were:

300 cpsi

0.04 mm stainless 347 foil

100 mm diameter, 150 mm long

Nickel‑based brazing

Lightweight high‑temp mat

Gap to can: 0.3 mm

Weight per substrate: 380 grams. A standard automotive version would have been over 600 grams.

They tested it to 700 degrees continuous, 800 spikes. No sagging. No cracks. Backpressure was within 2% of target.

They ordered 500 pieces. Then another 500. Last I heard, they've spec'd that substrate into two more aircraft platforms.

Lightweight and high‑temperature resistant are not opposites. You can have both – if you choose the right foil alloy, thin enough gauge, proper cell density, and a brazing process that handles thermal cycling.

Aircraft ECS converters don't need to be heavy. They don't need to be fragile. They just need to be engineered for that specific environment.

We've done it before. We can do it again.

If you're working on an ECS or any high‑temp, weight‑sensitive application, bring us your numbers. We'll tell you what's possible. And we'll build it.