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How We Build a Premium DOC Catalytic Converter – Step by Step on the Shop Floor
People think a DOC catalytic converter is simple. Just a metal can with some honeycomb inside. Braze it together, bolt it on, done.
I wish. If it were that easy, every cheap one on the market would last. They don't.
Making a premium DOC – one that actually survives on a diesel engine for years – takes a bunch of steps. And you have to get every one right. Miss one, and you're shipping a part that might crack, or plug, or just stop cleaning.
Here's how we actually build them. No fluff. Just what happens on our floor.
Step One – The Foil Has to Be Right
It all starts with metal foil. For a diesel oxidation catalyst, we use stainless. 304 for most jobs, 316 if there's salt or acid. Aluminum is out. Diesel exhaust has too much heat and vibration.
The foil thickness depends on the application. For a highway truck, 0.05 mm. For a loader or excavator, 0.08 mm. For a generator that runs 24/7, sometimes 0.1 mm.
Every coil gets checked when it comes in. Thickness at three spots. Surface for oil or scratches. We even run a test braze on a small coupon. If the braze doesn't stick, the whole coil goes back.
We learned that lesson years ago. A supplier changed their rolling process without telling us. The foil looked fine, but the brazing failed on three batches. Now we trust nobody.
Step Two – Forming the Corrugations
The flat foil goes through a set of forming rolls. Those rolls press the foil into a wavy shape – corrugations. The wavy strip gets sandwiched with a flat strip to make the honeycomb.
The rolls wear over time. We change them on a schedule, not when they break. Every hour, we check cell dimensions with a little gauge. If the gauge doesn't fit right, we stop the line.
For a DOC, cell density is usually 300 or 400 cpsi. 300 for heavy‑duty, 400 for lighter duty. We don't guess. We ask the customer about the engine, the load, the fuel.
Step Three – Stacking or Winding
Round DOCs get wound. We take the corrugated strip and flat strip together and wind them around a mandrel. Keep winding until we hit the right diameter.
Oval or rectangular DOCs get stacked. That's slower. You cut strips to length and stack them in a fixture, one layer at a time. The fixture has guide pins to keep everything square.
Stacking is harder than winding. One layer shifts, the cells get crooked. Crooked cells mean bad flow. We light‑test every stack before it goes in the furnace. Dark spots or streaks? That stack gets reworked.
Step Four – Brazing – The Heart of the DOC
The stacked or wound foil goes into a furnace. This is where the layers become one solid piece.
We put a brazing filler between the layers. For a diesel oxidation catalyst, we use a high‑temperature nickel‑based filler. Not the cheap stuff. It has to stay solid at 650°C.
The furnace heats up. The filler melts, flows into the joints, then solidifies. We control the temperature profile very tightly. Too cold, the filler doesn't flow – weak joints. Too hot, the filler runs everywhere and clogs the cells.
We log every cycle. Thermocouples inside the furnace, not just the controller. And every batch gets a peel test. We sacrifice one substrate, clamp a layer in a vise, and pull. If the foil tears before the braze lets go, it's good. If the braze separates clean, the whole batch is junk.
One night, the furnace drifted cold. Nobody noticed until morning. Peel test failed on three samples. We scrapped the whole batch. The operator was upset. But shipping bad parts would have been worse.
Step Five – Canning – Putting It in the Shell
The brazed core is still just a honeycomb. It needs to go into the metal can that bolts to the exhaust pipe.
We wrap the core in a mounting mat – a fiber material that expands when it gets hot. The mat holds the core tight and cushions it from vibration.
Then we press the wrapped core into the can. The fit has to be just right. Too tight, you crack the substrate. Too loose, it rattles. We control the gap to within a few tenths of a millimeter.
For a premium DOC, we sometimes add a mechanical retention ring – a metal lip inside the can that holds the substrate even if the mat loosens. Over‑engineered? Maybe. But on a diesel engine that shakes for 10,000 hours, it's cheap insurance.
Step Six – Coating – Where the Chemistry Lives
The bare metal does nothing. The catalyst is in the coating.
First, a washcoat – a ceramic slurry that creates a rough, porous surface. We dip the core, blow out the excess with air. Too much washcoat plugs the cells. Too little and you don't have enough surface area.
Then it goes through a drying oven and a firing furnace. The washcoat sinters onto the metal.
Next, the precious metals. Platinum, palladium – sometimes rhodium if the DOC also needs to reduce something. We dip the core in a liquid solution containing the metals. Then dry and fire again.
The metals end up as microscopic dots scattered across the washcoat. That's what actually cleans the exhaust.
We weigh the core before and after each coating step. The weight gain tells us the loading. For a premium DOC, we're generous with precious metals. Not skimpy. Because a diesel oxidation catalyst that loses activity after 1,000 hours is not a premium part.
Step Seven – Final Testing
Every batch gets tested. Not every single part – but samples from every batch.
Flow test. Put a sample on a flow bench, run air through, measure backpressure. If it's too high or too low, the batch doesn't ship.
Light test. Shine a light through. Dark spots mean clogged cells. Streaks mean crooked cells.
Peel test. We already did one on a raw substrate. We also do a peel test on a coated sample to make sure the washcoat didn't weaken the braze.
Thermal cycle test on new designs. Heat to 600°C, cool to room temp, repeat 200 times. Then look for cracks.
Vibration test on new designs. Mount in a can, shake at engine frequencies for 24 hours. Then check for loose mat or cracked braze.
We keep records on every batch. Foil coil number, forming tool, operator, furnace cycle, coating batch, test results. If a DOC comes back from the field, we can trace it.
What Makes a Premium DOC Different
Cheap DOC catalytic converters cut corners. Thinner foil. Cheaper brazing. Less precious metal. No testing.
A premium DOC does the opposite.
Thicker foil (0.08 mm instead of 0.05). High‑temp nickel braze. Heavy‑duty mounting mat. Retention ring. Generous precious metal loading. Full testing. Full traceability.
It costs more to build. It costs the customer more upfront. It lasts longer.
We've had fleet customers switch from cheap DOCs to ours. They paid 30% more per part. Their failure rate dropped 70%. Total cost per mile went down.
Bottom Line
Building a premium DOC catalytic converter is not rocket science. It's just doing a dozen small things right, every time, and not skipping steps.
Good foil. Precise forming. Solid brazing. Proper canning. Generous coating. Thorough testing. Full traceability.
We do all of that because we've seen what happens when you don't. Cracked substrates. Poisoned catalysts. Angry customers.
If you want a diesel oxidation catalyst that actually lasts, don't buy the cheapest one you can find. Buy one that's built like we build them. It costs more upfront. You'll forget that the first time you don't have to replace it.
How Industrial DOC Catalytic Converters Clean Up Generator Exhaust – What We've Learned from Real Installations
I've been to a lot of generator sites. Backup units for hospitals, prime power for factories, continuous run for telecom towers. One thing they all have in common – the engine runs steady. No stop‑and‑go. No idle for twenty minutes then full load. Just constant RPM, constant load, sometimes for days or weeks at a time.
You'd think that would be easier on a diesel oxidation catalyst than a truck engine. In some ways, it is. In other ways, it's harder.
We've supplied industrial DOC catalytic converters for dozens of generator installations. Some worked great. Some had problems we had to solve. Here's what we learned.
How a Generator DOC Is Different
A truck DOC has to handle thermal cycling – hot, cold, hot, cold. A generator DOC gets up to temperature and stays there. That's easier on the substrate. Less thermal stress, less cracking risk.
But a generator also runs for long stretches. A truck might run 8 hours a day. A prime power generator might run 24/7 for weeks. That means the diesel oxidation catalyst sees more total operating hours in a shorter calendar time.
And the flow rate is steady. No surges. So the DOC can be optimized for a narrow range of exhaust flow and temperature. That's actually good – you can dial in the cell density and coating exactly.
The challenge is often space. Generator enclosures are tight. The DOC has to fit in whatever space is left after the radiator, the alternator, the control panel. Sometimes that means a custom shape.
Real Installation – Hospital Backup Generator
We worked with a hospital in the Midwest. They had a 500 kW diesel generator for emergency backup. It ran a weekly self‑test for 30 minutes, plus occasional actual outages.
Their problem was smell. During self‑tests, the diesel exhaust would drift toward the emergency room intake. The hospital got complaints. They needed a DOC catalytic converter to cut the hydrocarbons.
We sized a 300 cpsi stainless DOC – 0.08 mm foil, heavy‑duty mat, standard precious metal loading. The exhaust temp during self‑test was around 350°C, plenty hot for the catalyst to work.
We installed it in the exhaust stack right after the turbo. The hospital did a before‑and‑after smell test. The difference was obvious. No more diesel stink near the ER intake. They've been running that DOC for three years now with no issues.
Real Installation – Factory Prime Power
Another customer ran a factory in Southeast Asia. The grid was unreliable. They had a 1 MW diesel generator running 18 hours a day, every day. That's a lot of hours.
Their problem wasn't smell – it was emissions compliance. The local environmental agency started enforcing limits on CO and hydrocarbons. The generator was old, no aftertreatment. They needed a DOC to get under the limits.
We spec'd a 200 cpsi diesel oxidation catalyst – lower cell density to keep backpressure down. The generator was already working hard. We didn't want to choke it. Foil thickness was 0.1 mm stainless. Heavy‑duty all the way.
We also added a temperature monitor before and after the DOC. The customer wanted to see light‑off time and conversion efficiency.
The DOC cut CO by 85% and hydrocarbons by 90%. The factory passed their emissions audit. The catalytic converter has been running for 8,000 hours now. Still working.
The Problem of Low Load
Not all generator applications are steady high load. Some generators run at low load for long periods – like a standby generator that only does light weekly tests.
At low load, the exhaust temperature might only be 200°C or 250°C. That's marginal for a DOC. The catalyst needs about 250–300°C to light off properly.
We had a customer with a generator that ran a 20‑minute self‑test at only 30% load. The DOC never got hot enough. Hydrocarbons weren't burning off. The smell was still there.
The solution was to either increase the load during self‑test or preheat the DOC with an electric heater. The customer chose to change their test procedure – they put a load bank on the generator during the weekly run. Got the exhaust temp up to 350°C. The DOC started working.
Lesson learned – a diesel oxidation catalyst needs heat. If your generator runs cold, don't expect miracles.
Fuel Quality Still Matters
Generator fuel is often delivered in bulk and stored in tanks for months. That fuel can degrade. It can pick up water or bacteria. And the sulfur content might be higher than on‑road diesel.
We saw a case where a generator DOC lost activity after only 1,000 hours. We cut it open. The washcoat had a grayish‑white deposit. Lab test said sulfur poisoning.
The customer tested their fuel. Sulfur was 800 ppm – way above the 15 ppm typical for on‑road diesel. They switched to a lower‑sulfur fuel and replaced the DOC. The new one is still going after 3,000 hours.
If you're running a generator on off‑road or bulk diesel, test your fuel. Sulfur kills DOC catalytic converters.
Sizing the DOC for Generator Flow
Generator exhaust flow is predictable. You know the engine displacement, the RPM, the load factor. So you can size the DOC precisely.
Too small and you get high backpressure. The generator loses efficiency, maybe even trips on high exhaust backpressure. Too big and the DOC takes too long to light off, and it wastes space and money.
We use a simple formula – face velocity around 2–3 meters per second at full load. That keeps backpressure low and light‑off fast.
For a 500 kW generator, that usually means a DOC about 10 inches in diameter and 12 inches long. But every engine is different. We ask for the engine specs before we quote.
Space Constraints in Generator Enclosures
Generator enclosures are packed. The diesel oxidation catalyst has to fit in the exhaust stack, which might have bends, silencers, and other components.
We've built DOC substrates in oval and rectangular shapes just to fit into tight enclosures. One customer had a generator with the exhaust pipe running between two structural beams. The only space was a 200mm by 150mm rectangle. We built a rectangular DOC to fit.
Custom shapes take more tooling time, but they work.
Maintenance and Monitoring
A generator DOC doesn't need much maintenance. But you should monitor a few things.
Backpressure. Install a pressure gauge before and after the DOC. If backpressure goes up, the DOC might be plugging with soot.
Temperature. A thermocouple before and after the DOC tells you when it lights off. If the temperature rise across the DOC drops, the catalyst might be losing activity.
Visual inspection. If you can, look at the DOC face during annual service. Soot buildup? Cracks? White deposits? All tell a story.
We provide customers with a simple log sheet. Record backpressure and temp rise every month. If numbers change, call us.
Bottom Line
Industrial DOC catalytic converters work well on generator exhaust – if you size them right, match the cell density to the load, and pay attention to fuel quality.
Steady temperature is easier on the substrate. But low‑load applications need preheating or higher test loads. Stainless foil, 300 cpsi, 0.08 mm thickness is a good starting point for most generators.
We've had successful applications on hospital backups, factory prime power, telecom towers, and even a landfill gas generator (special coating required). Every one taught us something.
If you have a generator that needs a diesel oxidation catalyst, tell us the engine model, the load profile, and the fuel you use. We'll spec a DOC that fits – and we'll help you avoid the problems we've already solved for other customers.
Why Aviation Manufacturers Choose Custom Catalytic Substrate Carriers (Not Off‑the‑Shelf)
Walk into any automotive parts warehouse, and you'll find a shelf full of catalytic converter substrates. Round. 400 cpsi. Aluminum or stainless. Pick a size, grab one, go.
Now try that for an aircraft. You won't find a shelf. Because there is no standard.
Every aviation manufacturer I've worked with – APU builders, ECS suppliers, even ground support equipment makers – they all need something different. Different shape, different cell density, different material, different mounting. Off‑the‑shelf doesn't exist.
Why? Because aircraft aren't cars. And the substrate carriers have to fit the aircraft, not the other way around.
Here's why they always come to us for custom.
Space Is Never Standard
A car has room under the floor. Not a ton, but enough for a round can.
An aircraft has no spare room. The APU is crammed into the tail cone. The ECS is buried in the belly, surrounded by ducts and valves and wiring bundles. The space left for a catalytic converter is whatever happens to be leftover after everything else is designed.
That leftover space is never round. Sometimes it's oval. Sometimes rectangular. Sometimes a weird D‑shape to clear a structural rib.
One customer sent us a cardboard template they'd made by pressing it into the cavity and tracing the edges. That was their "drawing." We built a custom oval substrate carrier to match.
Off‑the‑shelf round parts wouldn't fit. They'd have to redesign the whole compartment. That's not happening. So they call us.
Heat Is Higher and More Constant
An aircraft APU runs for hours at high power. No coasting. No stop‑and‑go. Just steady, hot exhaust.
Temperatures hit 650, 700, sometimes 750 degrees Celsius. That's way above what a car converter sees.
Standard automotive substrates – even the stainless ones – start to creep at those temps. The foil sags. The cells distort. The carrier loses shape.
So we build custom with higher alloys. 347 stainless. Inconel when it's really hot. Not off‑the‑shelf. The customer tells us their max temp, and we pick the material.
One APU builder tried a standard 304 stainless substrate from another supplier. It sagged after 500 hours. They switched to our custom 347 part. No sag at 2,000 hours.
Vibration Is a Different Beast
A car engine vibrates. But an aircraft APU vibrates at different frequencies, and the airframe adds its own shaking.
Standard mounting mats – the fiber wrap that holds the substrate in the can – aren't always enough. They can take a set, or they can loosen up over time.
For aviation, we add mechanical retention. A ring or a lip inside the can that holds the substrate even if the mat fails. That's not standard. That's custom.
We also adjust the foil thickness. Thicker than automotive – 0.08 mm or 0.1 mm – to handle the shaking. The weight penalty is worth the durability.
One customer had a vibration issue that kept cracking their substrates at the brazed joints. We went to a thicker foil and a softer, more flexible brazing filler. The cracking stopped.
Flow Requirements Are Different
An aircraft ECS moves a lot of air. Hundreds of pounds per hour. The substrate can't create much backpressure, or the whole system loses efficiency.
Standard 400 cpsi is often too restrictive. So we go custom with lower cell density – 200 or 300 cpsi. Bigger cells, less restriction.
But lower cell density means less surface area for the catalyst. So we have to balance. Sometimes we lengthen the substrate to compensate. Sometimes we use a more active coating.
There's no standard recipe. Every application gets its own calculation.
Weight Is Always Watched
Aircraft manufacturers weigh everything. A few grams here, a few there – it adds up.
Standard substrates are designed for durability, not weight. They use a certain foil thickness, a certain mat density, a certain can wall thickness.
We can shave weight by using thinner foil, lighter mats, and shorter lengths – but only if the operating conditions allow it.
One ECS customer needed a substrate that weighed under 200 grams. Our standard version was 280 grams. We went to 0.04 mm foil, a lightweight mat, and shortened the length by 10mm. Got it down to 185 grams. Passed all their tests.
That's custom. You don't find that on a shelf.
Materials Must Match the Environment
Not every aircraft application needs Inconel. Some are fine with 304 stainless. Some need 316 for corrosion resistance. Some need aluminum for weight, but only if the temperatures are low.
Standard suppliers stock one or two materials. We stock many, and we'll use whatever the customer's environment demands.
We had a customer building an ECS for a seaplane. Salt air everywhere. They needed 316L stainless for corrosion resistance, not 304. We built it. Off‑the‑shelf suppliers didn't even offer 316L in their catalog.
Certification and Traceability Aren't Optional
Aviation manufacturers don't just want a part. They want a paper trail.
They need to know the foil supplier. The batch number. The braze cycle. The test results. They need a certificate of conformance for every shipment.
Standard substrate suppliers often don't keep that level of traceability. They buy foil in bulk, run production, and ship. If something fails, they can't tell you which coil it came from.
We can. Every custom batch gets a unique number. We record everything. When an auditor asks, we have the answers.
That's a big reason aviation customers stick with us. Not just the part – the paperwork.
Testing Is Never "Standard"
A car substrate gets a flow test and a visual. Maybe a thermal cycle if the manufacturer is thorough.
An aviation substrate gets thermal cycle to 500 or 700 degrees, hundreds of cycles. Vibration testing at aircraft frequencies. Sag testing under load. Coating adhesion testing.
We don't have a "standard" test package. We ask the customer what their qualification requires, and we run those tests.
One customer needed a substrate that could survive 1,000 thermal cycles from –50°C to 650°C. That's insane. But we built a batch, tested it, and it passed. The data went into their certification package.
Real Examples
An APU manufacturer needed a custom oval substrate to fit between two structural members. Standard round wouldn't fit. We built a 300 cpsi, 0.08 mm stainless 347 part with a heavy‑duty mat and retention ring. They've ordered over 1,000 pieces.
An ECS supplier needed a lightweight substrate for ozone conversion. Space was tiny. We used 0.04 mm stainless, 400 cpsi, 60mm long. Weight was under 150 grams. They tested it to 500 thermal cycles. No cracks. They're on their third production order.
A ground support equipment maker needed a high‑flow substrate for a diesel APU simulator. Low backpressure was critical. We used 200 cpsi, 0.05 mm stainless, and a low‑density mat. They measured backpressure at 2% of their previous supplier's part. Engine ran cooler. They switched all their production to us.
Aviation manufacturers choose custom catalytic substrate carriers because off‑the‑shelf doesn't work for them.
Different shapes for tight spaces. Higher alloys for high heat. Thicker foil for vibration. Lower cell density for flow. Lighter construction for weight. Full traceability for certification. Testing that matches their requirements.
We don't have a catalog. We have a shop and a set of tools. When a customer calls with a sketch and a list of requirements, we listen. Then we build.
If you're in aviation and you need a substrate carrier that doesn't come from a shelf, give us a call. Bring your space constraints, your temperature specs, your vibration data. We'll figure it out. We've done it before. We'll do it again.
Our Catalytic Converter Substrates Meet NASA & International Aerospace Emission Standards – Here's What That Actually Means
People throw around the term "aerospace grade" like it's some magic stamp. But what does it actually mean for a catalytic converter substrate? I've had customers ask if our parts are "NASA certified." NASA doesn't certify substrates. That's not how it works.
But we have built substrates for systems that ended up in NASA‑funded programs. And we've made plenty for aircraft APUs, ECS ozone converters, and ground support equipment that has to meet ICAO and EPA standards.
Here's what "aerospace grade" really requires – no marketing fluff.
NASA Doesn't Certify Substrates, But They Set the Bar
NASA doesn't have a single document that says "catalytic converter must meet this spec." But they've funded a lot of catalyst research over the years, and those performance targets have trickled down into commercial aerospace.
Look at the work NASA's Marshall Space Flight Center did with Precision Combustion on high‑temperature catalytic oxidizers for extended spaceflight. Those systems have to work from –100°C up to 500°C or more. That's a way wider range than any car converter sees. And they have to work the first time, every time, because there's no roadside assistance in space.
Another NASA project looked at breaking down toxic gases from solid waste processing on spacecraft. Same idea – fail‑safe, zero‑tolerance performance.
We've never gotten a direct purchase order from NASA. But we've sold substrates to aerospace companies who were building hardware for NASA‑related programs. They gave us their temperature specs, their vibration requirements, their thermal cycle counts. We met them. That's the closest you get to "NASA qualified" in this business.
ICAO and EPA – The Real Rules for Aircraft Emissions
If you're putting a converter on an aircraft engine or APU, the actual regulations come from ICAO and the EPA.
ICAO Annex 16, Volume II is the international standard. The current edition took effect in July 2023. It covers everything from engine emissions standards to certification procedures. There's a whole working group – CAEP – that keeps tightening the limits. They just agreed to stricter CO₂ rules for new aircraft types by 2031.
For the U.S., it's 40 CFR Part 87. That covers aircraft engine emissions, including APUs. APUs don't make up a huge percentage of airport emissions – less than 1% – but airports still care. Some major hubs restrict APU run time or require emissions controls.
We've supplied substrates for APU converters that helped customers meet those local air quality rules. No magic trick. Just a well‑designed substrate that actually cleans the exhaust.
SAE and AS9100 – The Quality Paperwork
This part is boring, but aerospace customers care about it more than you'd think.
AS9100 is the aerospace version of ISO 9001. It's not about the part itself – it's about how you make it, track it, and prove it. For any component going into an aircraft or ground support system, your supplier better have AS9100‑aligned processes.
That means full traceability. Every substrate gets a batch number. We know which coil of foil, which forming tool, which operator, which furnace cycle. If a customer calls with a problem, we can trace that part back to the shift it was made.
SAE also publishes standards like ARP9062 (operator self‑verification) and ARP9113 (supply chain risk management). We don't quote those by number in our sales pitch. But our processes follow the intent.
Jet Fuel Is Dirtier Than You Think
People assume jet fuel is clean. It's not.
ASTM D1655 allows up to 3,000 ppm sulfur. That's 3,000 parts per million. Compare that to ultra‑low sulfur diesel for cars – 15 ppm. Jet fuel is literally 200 times dirtier on sulfur.
Sulfur poisons precious metal catalysts. So an aerospace substrate has to be built differently. Higher precious metal loading. Poison‑resistant washcoat. More margin.
We learned this the hard way on an early APU project. Standard automotive‑style substrate died fast. Switched to a high‑sulfur formulation, and it lasted. Now we ask every aerospace customer about fuel sulfur content before we quote.
What "Aerospace‑Grade" Looks Like in Our Shop
So after all that, here's what we actually change when someone says "this is for an aircraft."
Material. Stainless. Always. Aluminum is fine for a Honda Civic. Not for something that sits near a hot APU or lives in an ECS compartment. For extreme heat, we go to Inconel.
Cell density. Lower than automotive. Usually 200–400 cpsi. High cell density creates backpressure, and aircraft systems hate backpressure.
Foil thickness. 0.04 to 0.08 mm. Thin enough to save weight – and aircraft customers weigh everything. Thick enough to survive vibration. The final number depends on how much shaking the part will see.
Brazing. High‑temperature nickel‑based filler. Not the standard stuff. It has to stay solid when the APU is running.
Mounting mat. Heavy‑duty, high‑temp rated. And we control the gap between the substrate and the can to within a few tenths of a millimeter. No rattling. Ever.
Testing. Thermal cycle (200+ cycles from room temp to 700°C). Vibration. Flow bench at temperature. Plus our standard peel tests and light tests.
Paperwork. Coil certs. Braze logs. Dimensional reports. Batch traceability. You want to see a certificate for the foil? We have it. You want to know what furnace run your parts came from? We can tell you.
Real Jobs We've Done
We made an oval stainless substrate for a business jet ECS ozone converter. The customer tested it. Ozone removal was over 99%. They ordered hundreds.
We built a small, heavy‑duty substrate for a regional jet APU. The vibration environment was brutal. We used thicker foil and a denser mat than usual. It lasted through 2,000 hours of testing. The previous supplier's part cracked at 500.
And we've sold raw honeycomb to a systems integrator who builds environmental control hardware for NASA‑funded research. I can't name the program. But the temperature range they asked for was way outside anything we do for cars. We figured it out.
Bottom Line
"Aerospace grade" isn't a sticker you put on a box. It's a list of real requirements. ICAO emissions. EPA Part 87. AS9100 traceability. Sulfur‑resistant washcoat. Thermal cycling. Vibration testing. Paperwork that proves everything.
We've built substrates that meet those requirements. Not for every aircraft application out there – but for enough of them that we know what works.
If you need a catalytic substrate for an aircraft APU, an ECS ozone converter, or ground support equipment, bring us your specs. We'll tell you what we've done for other customers in your space. And we'll build you a part that passes the test – not just on paper, but when your quality auditor checks the batch number.
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Rogabet Notepad 2026-0427
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High‑Reliability Catalytic Substrates for Aircraft Exhaust Systems – Solving Extreme Environment Pain Points
This one came from a Tier 1 aerospace supplier. They made exhaust components for regional jets. Not the engine itself – the exhaust system downstream of the turbine. They had a problem with a catalytic converter that kept failing.
The converter was supposed to clean up emissions from an auxiliary power unit. The APU runs when the plane is on the ground. It provides power and air conditioning. But the exhaust from an APU is nasty – high heat, high vibration, and the space is crammed into the tail cone, where everything is hot and nothing has room to breathe.
Their existing substrate from another supplier would crack after about 500 operating hours. Sometimes less. They'd pull the converter, see the honeycomb broken into pieces. They tried thicker foil. Tried different coatings. Nothing worked.
They came to us because they heard we did custom work for tough environments.
The Pain Points
We flew out to their facility – my first time in an aerospace plant. Everything was clean. Too clean. But the problem was real.
They laid out three big issues.
Heat. The APU exhaust hit 650 degrees Celsius continuous. Spikes to 750 during certain cycles. Most catalytic substrates start to soften around 600. Aluminum would turn to putty. Even standard stainless would creep over time.
Vibration. The tail cone of a jet is not a smooth place. The APU shakes. The airframe shakes. The exhaust system shakes with everything. Their old substrate was cracking along the brazed joints – classic vibration fatigue.
Space. The converter had to fit into a cylindrical can that was only 4 inches in diameter and 6 inches long. Small. That meant the cell density had to be just right – too many cells and backpressure would spike, too few and the emissions wouldn't clean up.
Also, weight mattered. Not as much as on a wing, but every pound still counted.
What We Did Differently
We didn't just send them a sample. We spent a week going through their data. Vibration logs. Temperature profiles. Backpressure requirements. Emissions targets.
Then we built a prototype batch of 20 substrates.
Material. We used Inconel 625. Not stainless. Not aluminum. Inconel. It's a nickel‑chromium alloy that stays strong at 750 degrees. Expensive as hell. But it doesn't creep, doesn't oxidize, doesn't crack. For an APU that runs thousands of hours, it was worth it.
Cell density. 300 cpsi. Lower than standard automotive. Bigger cells meant less backpressure through that small can. And the bigger cells were less likely to plug from any soot the APU made.
Foil thickness. 0.08 mm. Thicker than automotive, but not as thick as industrial. We balanced durability with light‑off time. The APU runs continuous, so fast light‑off wasn't critical.
Brazing. We used a high‑temperature nickel‑based brazing filler. Melting point over 1,000 degrees. It would never soften in the APU exhaust.
Mounting mat. We used a dense, high‑temp mat that doesn't take a permanent set. Designed for vibration. We also added a secondary retention ring inside the can – a metal lip that held the substrate in place even if the mat lost tension.
The whole thing weighed about 30% more than their old aluminum substrate. But it was still under their weight budget.
Testing – Real World, Not Just Lab
They didn't just put our substrates on a shaker table. They put them on an actual APU, in a test cell, running real cycles.
Four hundred hours of continuous operation, with temperature spikes to 750 every few hours. Then they shut it down, let it cool to ambient, and started again.
We did 2,000 hours of testing. That's about five times their old substrate's lifespan.
After 2,000 hours, they cut the converter open. The Inconel substrate looked almost new. No cracking. No sagging. The brazed joints were solid. The mat was still tight.
They did a second test on a different APU. Same result.
After that, they ordered 100 pieces for fleet trials. Those have been running for two years now. No failures.
What We Learned
Inconel works. It's expensive – about four times the cost of stainless. But for an aerospace application where a failure means a plane on the ground, that cost is worth it.
Brazing Inconel is different than brazing stainless. The filler has to match the alloy. We had to adjust our furnace cycle – higher temperature, longer soak. The first few samples had incomplete braze flow. We tweaked the cycle and got it right.
The retention ring was a good addition. The mat alone might have held, but with the ring, there's no chance of the substrate moving. Over‑engineered? Maybe. But in aerospace, that's the standard.
Also, documentation. Aerospace customers want a paper trail for everything. Foil certs, braze logs, test reports, dimensional data. We had to upgrade our record‑keeping. But now we have it, and it helps with all our customers.
What the Customer Said
Their project engineer told me: "We've tried four other suppliers. Your Inconel part is the only one that survived our full test cycle. We're spec'ing it into our new platform."
The purchasing guy said: "The price made me choke. But the zero failures made it worth it. We haven't had a single warranty claim on these."
Aircraft exhaust systems are not forgiving. High heat. High vibration. Tight spaces. Long operating hours. Most standard substrates – even good stainless ones – can't handle it.
But Inconel can. With the right cell density, the right brazing, and a mounting system that won't let go.
We built that substrate for one aerospace customer. Now we've made it for two others. The tooling is dialed in. The process is repeatable.
If you have an extreme environment – aviation, military, high‑temp industrial – talk to us. We'll tell you if Inconel is the answer. And if it's not, we'll find something that is. We've done it before.
Case Study: Lightweight & High‑Temperature Resistant Catalytic Substrates for Aircraft
A few years ago, a company that makes environmental control systems for business jets called us. They had a problem. Their ECS – the system that manages cabin air pressure and temperature – needed a catalytic converter to clean up bleed air from the engine. But the space was tiny. The heat was brutal. And weight was critical.
They'd tried a few suppliers. The parts were too heavy. Or they couldn't handle the temperature. Or they cracked on the test rig.
They asked if we could do something lighter and tougher.
The Problem
The ECS sits in the belly of the aircraft. Not much room. The converter had to fit in a can that was barely 100mm in diameter and 150mm long. But it had to process a lot of air flow.
Standard 400 cpsi substrates were too restrictive. Backpressure would be too high. So they needed lower cell density – around 200 cpsi – to keep the air moving.
But here's the kicker. The bleed air coming off the engine could hit 750 degrees Celsius. That's way hotter than a car converter ever sees. Most metal honeycomb would soften and sag at that temp. Aluminum is out of the question. Even standard stainless can struggle.
And the whole assembly had to be light. Every gram matters on an airplane.
What We Proposed
We went back and forth with their engineers for a few weeks. They sent us a drawing of the can. We sent back substrate specs.
We settled on 200 cpsi – bigger cells, less backpressure. Foil material: 347 stainless steel. Not the common 304 or 316. 347 has better high‑temperature creep resistance. It doesn't sag as much when it's hot for a long time.
Foil thickness: 0.04 mm. That's thinner than our standard automotive foil. Lighter, and less metal to heat up. But thin foil is fragile. We had to be careful with handling and brazing.
We also used a special high‑temperature brazing filler. Normal filler would melt at 750 degrees. This one had a higher melting point, so it wouldn't soften during operation.
The substrate was round, small – just 95mm diameter, 140mm long. We made a few samples and sent them over.
The Testing
They put our substrates through a rig that simulated real ECS conditions. Hot air at 750 degrees, flowing through for hours. Then cooling down. Then heating up again. Dozens of cycles.
First test: The substrate didn't sag. Cells stayed round. Good.
Second test: They measured backpressure before and after cycling. No change. That meant the foil hadn't deformed.
Third test: Vibration. They shook it at frequencies typical for the aircraft belly. Our substrate held together. The brazing didn't crack.
Then they coated it with their own catalyst formula and ran an emissions test. Passed with margin.
The weight? Our 0.04 mm foil cut about 30% of the mass compared to a standard 0.05 mm substrate. Not huge, but for aerospace, every gram counts. They were happy.
What Made It Work
The 347 stainless was the key. Most people think 304 is fine for high heat. It's not. Not at 750 degrees continuous. 347 has columbium and tantalum added. Those elements prevent chromium carbide precipitation – basically, it stays strong and doesn't crack.
The thin foil was a risk. 0.04 mm is delicate. We had to adjust our stacking fixtures to avoid denting the edges. And the brazing cycle had to be dialed in perfectly – too hot and the thin foil would warp, too cold and the braze wouldn't flow.
We also had to be careful with the mounting mat. Standard mats start to break down above 600 degrees. We used a high‑temperature mat rated for 800 degrees. It cost more, but it wouldn't turn to dust.
The Result
The customer ordered a small batch first – 50 pieces. Then 200. Then they put our substrate into production for that ECS model.
We've been shipping to them for three years now. No field failures that I know of. Their buyer told me once, "You're the only supplier who got the thermal stability right."
We also learned a few things. Thin foil is doable, but you have to handle it like glass. And 347 stainless is worth the extra cost for extreme heat.
What We'd Do Different Next Time
If another aerospace customer came with a similar request, we'd do a few things faster.
We'd test the brazing filler at temperature before committing to production. That first batch, we had to re‑braze a few samples because the filler didn't flow right. Now we have a qualified process.
We'd also recommend a thermal barrier coating on the outside of the can. We didn't do that – the customer handled it themselves. But it helps keep the substrate from seeing the full peak temperature.
And we'd quote a longer lead time for the first batch. Tooling and process development always takes more time than you think.
Aircraft environmental control systems are not cars. The temperatures are higher. The space is tighter. The weight limit is stricter.
But a metal honeycomb substrate can still work – if you pick the right alloy, the right thickness, the right brazing, and the right mat.
We did it for one ECS supplier. We can do it for others.
If you need a lightweight, high‑temperature catalytic substrate for aviation or any other extreme application, give us a call. Bring your drawings. We'll figure it out.
Catalytic Substrates That Actually Meet Global Emission Standards – EPA, Euro 6, China 6, Bharat VI
If you sell catalytic converters in more than one country, you know the headache. One customer needs EPA. Another needs Euro 6. Some ask for China 6. India wants Bharat Stage VI.
Different names. Different test cycles. Different limits.
But here's the thing – a good substrate doesn't care about the name on the regulation. It just has to clean the exhaust enough to pass whichever test they throw at it.
We've been shipping substrates all over the world for years. We've learned what it takes to meet each standard. Not by reading the rulebooks – by having customers come back and tell us "it passed."
What All These Standards Have in Common
EPA, Euro 6, China 6, Bharat VI – they all want the same outcome. Less CO, less hydrocarbons, less NOx. They just measure it differently and set different deadlines.
EPA is the US standard. Focuses on tailpipe emissions over a specific driving cycle. Pretty strict on NOx for diesels.
Euro 6 is Europe. Tougher on particulates than EPA. Also has real‑driving emissions testing, not just lab cycles.
China 6 is basically Euro 6 with Chinese characteristics. Same technology, same approach. But they moved fast – went from China 5 to China 6 in a few years.
Bharat Stage VI is India's version. Equivalent to Euro 6 but adapted for Indian driving conditions. Hotter, dustier, more stop‑and‑go.
The common thread? They all need a substrate that lights off fast, stays active, and doesn't cost a fortune.
What We Do to Meet These Standards
We don't make one substrate for EPA and another for Euro 6. That's not how it works.
The substrate itself – the metal honeycomb – is the same. It's the cell density, wall thickness, foil material, and coating that change.
For most of these standards, 400 cpsi with 0.05 mm foil is the baseline. That cleans well and flows well. Good for gasoline engines across all regions.
For diesels, we go to 300 cpsi with thicker stainless foil. Lower backpressure, handles heat better.
The real difference is the coating. That's where the precious metals do the work. For tough standards like Euro 6 and China 6, we increase the precious metal loading. More platinum, more palladium, more rhodium. Or we adjust the ratios.
We don't guess. We work with coating partners who have tested their formulations on real engines. They know what loading gets you under the limit for each standard.
EPA – The Old Reliable
EPA has been around a long time. The test cycles are well understood. A good substrate with proper coating will pass.
The challenge is durability. EPA requires the converter to last a certain number of miles. So the substrate has to hold up – no cracking, no delamination, no coating loss.
We use stainless foil for most EPA diesel applications. Aluminum is fine for gasoline. And we test our brazing to make sure it doesn't come apart.
We've had customers pass EPA with our substrates. They come back for more. That's how we know it works.
Euro 6 – Tougher on Real Driving
Euro 6 introduced RDE – real driving emissions. They drive the car on the road, not just on a dyno. That means the converter has to work in cold weather, uphill, with a heavy foot.
That's harder on the substrate. More temperature swings. More vibration. More chance of the catalyst not being fully warm.
For Euro 6, we recommend stainless foil for anything but the mildest applications. And we pay extra attention to the mounting mat – it has to hold the substrate tight through all those real‑world bumps.
A customer in Germany told me once, "We tried your competitor's substrate on RDE. Failed the cold start part. Switched to yours. Passed." That's real feedback.
China 6 – Fast and Furious
China moved from China 5 to China 6 in record time. That meant everyone scrambling to upgrade their aftertreatment systems.
China 6 is similar to Euro 6, but the testing is done in Chinese conditions – more traffic, more idling, different fuel quality.
For China 6, we see a lot of demand for higher cell density – 600 cpsi in some cases. More surface area to catch emissions when the engine is running in stop‑and‑go.
Also more demand for stainless. The heat is real, and the roads are rough. Aluminum doesn't always last.
We ship a lot to China now. Our partners there test the substrates. They tell us what works. We adjust.
Bharat Stage VI – The New Kid
India jumped from BS IV to BS VI directly. Skipped BS V entirely. That was a huge change for the industry.
BS VI is basically Euro 6. Same limits, same test cycles. But Indian driving is different. Hotter ambient temps. More dust. Stop‑and‑go traffic that never ends.
For BS VI, we recommend stainless foil almost always. The heat and dust will kill aluminum. And we go with lower cell density – 300 cpsi – so the cells don't plug up from dust and soot.
One of our customers in Pune told me they tried 400 cpsi aluminum. Failed in six months. Switched to our 300 cpsi stainless. Still running after two years.
How We Verify Compliance
We don't have our own emissions lab. That's not our job. We make the substrate, not the finished converter.
But we work with customers who do have labs. They test our substrates with their coatings and their cans. Then they tell us if it passes.
We keep records of every test. Which substrate, which coating, which engine, which standard. That data helps us recommend the right spec for the next customer.
If you need a substrate for a specific standard, we don't guess. We look at what worked for other customers with similar requirements. If we don't have data, we find a lab to test it.
What We Don't Do
We don't claim our substrates are "certified" for EPA or Euro 6. The finished converter gets certified, not the substrate alone.
We also don't sell you a substrate that we haven't seen work for someone else. If you ask for China 6 and we've never made that part for a China 6 application, we'll tell you. Then we'll work with you to test it.
Honesty is better than a broken promise.
Selling catalytic converters in multiple countries means your substrate has to handle different standards – EPA, Euro 6, China 6, Bharat VI.
The honeycomb itself isn't magic. It's about cell density, wall thickness, material, and coating. We have recipes for each standard. We've tested them with customers. They work.
We don't promise a certificate. We promise a substrate that has passed real emissions tests in real engines. That's worth more than a piece of paper.
If you're exporting converters, talk to us. We'll tell you what other customers in your target market are using. And we'll ship you the same thing. No guesswork. Just what works.