How a Catalytic Converter Works and Why It Can Not Improve Fuel Efficiency

A catalytic converter is one of the most common devices found on a vehicle. Whether it is a passenger vehicle or a light duty pickup; a heavy-duty pickup, dump truck or semi-tractor trailer; or a piece of heavy equipment, almost all vehicles and machines that burn fossil fuel for the purpose of transport, excavation or agriculture have a catalytic converter. The reason being, a catalytic converter is required by governing bodies around the world. 

From the United States Government to the European Union, governing bodies require the manufacturers of over-the-road vehicles to equip their cars, pickups, trucks, and semi-tractor trailers with catalytic converters. Additionally, most heavy equipment also requires the addition of a catalytic converter prior to being sold. 

However, the question, what is a catalytic converter is somewhat of a mystery. 

The reason most people are less familiar with catalytic converters — what they are and how they work — than other components of an engine is because unlike most other components of a vehicle, catalytic converters rarely fail. 

Amateur mechanics know what starters and alternators and solenoids (relays) are because they go bad. Neophyte mechanics understand what water and fuel pumps are because of the fail regularly, but aren’t that difficult to replace. People know what radiators and heads and exhaust manifolds are because they leak and/or crack or both. Even if a person doesn’t understand how it works, most are aware that modern vehicles have onboard computer systems because they go bad.

Catalytic converters, on the other hand, are extremely resilient.

Even though most people have heard of catalytic converters and are aware their vehicle or machine has one, it is no surprise that not everyone knows where a catalytic converter is housed on an engine or how it works. Catalytic converters usually outlast an engine for one thing. And for another, even if a catalytic converter does go bad, it is extremely difficult to know a catalytic converter is on the outs because it does not affect engine performance. Without an emissions test, it is likely a person would never know if their catalytic converter has gone kaput. 

About all most people who aren’t professional mechanics know about catalytic converters is that catalytic converters reduce emissions. Some people are also aware of the fact that in most countries it is illegal to remove a catalytic converter from a street-legal vehicle. 

What, Exactly, Is a Catalytic Converter and where is it Found on a Vehicle

A catalytic converter is a mechanical device housed on the exhaust system of a vehicle or machine. In size and shape, a catalytic converter resembles a muffler. Catalytic converters are typically oblong or round cylinders and exhaust is fed in one end and exits the other. A catalytic converter is typically found a few inches or feet from the exhaust manifold on the tailpipe. 

Inside a catalytic converter, there are a series of plates. Each plate is made of ceramic monolith substrate, a honeycomb-like material through which exhaust can pass. Exhaust is fed into the catalytic converter intake, passes through the monolith substrate of the plates, and back out the catalytic converter.  

What is a Catalytic Converter Made Of?

A catalytic is one of the most expensive components — with respect to the monetary value of the actual components — associated with a spark-fired or compression engine. That is because a catalytic converter is made of precious metals. According to SpecialtyMetals.com — a company that recycles, refines, and pays customers for used catalytic converters — the precious metals found in a catalytic converter include palladium, rhodium, copper, nickel, cerium, iron, and manganese,  but, “Platinum is the catalyst in a catalytic converter.”

It is the catalyst that gives a catalytic converter its value, both monetary value and its value as emissions reducing device.

The word catalyst is thrown around a great deal, particularly in the auto industry. The manufacturers of fuel additives and fuel treatments, in particular, take great liberties with the word. Additive and treatment marketers label their products catalysts even though they are not. No fuel additive nor treatment is — nor contains — a true catalyst. 

Treatments, additives, and detergents can catalyze change, but that does not mean they are catalysts. 

There are two types of catalysts: noble metals and enzymes. Catalysts are unique in that they can do something that is extremely rare. Catalysts can generate a change in a chemical compound — diesel or gasoline, for example — without themselves undergoing any change. 

As such, the catalyst in a catalytic converter — platinum — can reduce emissions without changing or degrading.

What Does a Catalytic Converter Do?

There is no engine manufactured that burns fuel 100 percent efficiently. In fact, combustion and compression engines are extremely inefficient at burning fossil fuels, particularly those fossil fuels which high energy densities like diesel. If an engine that could burn gasoline, diesel, or any other fossil or biofuel completely, the only emissions would be carbon dioxide and water. In other words, it isn’t so much that fossil fuels are dirty when combusted, it is that the technologies we use to burn fossil fuels are extremely limited. After all, carbon dioxide and water are both non-toxic even though they are both greenhouse gases.

As we do not have the capacity to create an engine that burns fossil fuels completely, the engines we use produce a wide variety of emissions, only a portion of which are CO2 and water. Emissions from vehicles include particulate matter; hydrocarbons (the chemical compounds in fossil fuels that combust); nitrogen oxides; carbon monoxide; sulfur dioxide; cancer-causing toxic emissions like benzene, acetaldehyde, and 1,3-butadiene; and greenhouse gases.

Almost all of the emissions produced by the incomplete burning of fuel are toxic. A catalytic converter reduces the number of toxic emissions by combusting the unburned fuel or re-burning the partially burned fuel found in emissions. 

How Does a Catalytic Converter Reduce Emissions?

Again, a catalytic converter burns the unburned fuel in emissions and completes the combustion process of partially burned fuel found in emissions. Though ingenious, the means by which a catalytic converter completes the combustion process is extremely simple. 

When exhaust containing unburned and partially burned fuel exits an engine’s exhaust manifold, it feeds into the catalytic converter. The exhaust is extremely hot. As such, the exhaust superheats the noble metal catalyst(s) found in the monolith substrate plates inside the catalytic converter — again; the catalyst in a catalytic converter is typically platinum. 

Once sufficiently heated, the catalysts in the converter begin to combust the unburned and partially burned fuel that arrives with the exhaust that follows. A catalytic converter is a perpetual cycle mechanical device. Exhaust from the engine superheats the catalysts in the converter as it passes through and, once hot enough, the catalysts begin combusting the unburned and incompletely burned fuel in the exhaust that follows. 

Does a Catalytic Converter Improve Gas Mileage?

No, a catalytic converter does not improve gas mileage. In fact, because of the back pressure, a catalytic converter creates, catalytic converters reduce gas mileage. In this respect, catalytic converters and mufflers are the same. Without a catalytic converter and a muffler, a vehicle actually gets noticeably better fuel economy. 

But, it isn’t only because of back pressure that catalytic converters do not improve fuel economy. Catalytic converters cannot improve fuel efficiency because catalytic converters are post-combustion mechanical devices. Catalytic converters do not play a role in either the pre-combustion state of a fossil fuel nor do catalytic converters play any part in the actual combustion of fuel during the portion of the engine combustion process that produces energy. 

All the energy produced by a catalytic converter — when it combusts the unburned and partially burned fuel in exhaust — is lost as heat. None of the energy produced by a catalytic converter is converted into energy that propels a vehicle. 

What Mechanical Devices Improve Gas Mileage?

In order for a mechanical device to improve gas mileage, the mechanical device must interact with the fuel combustion process of an engine prior to or during combustion. While that fact may seem obvious, it requires clarification because there is a misconception that catalytic converters can increase fuel economy. Again, a catalytic converter cannot improve “gas” mileage.

Pre-combustion fuel catalysts, on the other hand, can — and do — increase fuel economy.

What is a Fuel Catalyst?

A pre-combustion fuel catalyst is a mechanical device that resembles a catalytic converter, though the casing is made of much stronger and resilient materials, at least in the case of the Rentar Fuel Catalyst. And, like a catalytic converter, the active agents in fuel catalysts are noble metals. 

But, unlike a catalytic converter that combusts unburned or incompletely burned fuel, the noble metals in a fuel catalyst produce a change in the fuel prior to its combustion. 

What Does a Fuel Catalyst Do?

There are a number of reasons engines do not combust fuel completely, but the most elemental reason is oxygenation, or the lack thereof. The combustion of any fossil or biofuel requires oxygen. In fact, the combustion of fossil and biofuels only requires three elements: oxygen, carbon, and hydrogen. When hydrogen and carbon chemical compounds — hydrocarbons — bond with oxygen, the result is a highly combustible, energy-producing molecule. 

However, if hydrocarbons are unable to mix with oxygen or mix with oxygen at the requisite ratio, the result is unburned fuel or partially burned fuel, both of which result in toxic emissions. 

A fuel catalyst conditions fuel in a manner that optimizes hydrocarbon oxygenation.

Why Don’t Hydrocarbons Always Oxygenate or Oxygenate at the Right Ratios?

Molecular chains are polarized. In addition to creating chemical bonds, polarization also creates physical bonds. While the physical bonds between molecules do not create new molecules, they do create clusters. Simply, the molecular chains in fossil and biofuels cluster together in groups. When closely aligned, fuel molecules — hydrocarbons — do not oxygenate well because there is a lack of surface available for which oxygen atoms to attach. 

Hydrocarbon clusters are a particularly common issue with fuels that have long molecular chains and high carbon-to-hydrogen ratios. Fuels with high carbon-to-hydrogen ratios have, by definition, high energy density. Fuels that are high in energy density include diesel, kerosene (jet fuel), and anthracite coal. 

But, while high energy density fuels have great energy potential, they are also the most difficult to combust consistently. Again, this is because high-density fuels do not oxygenate as readily as low energy density fuels.  

How Does a Fuel Catalyst Increase the Oxygenation Potential of a Fossil Fuel?

The noble metal catalysts in a fuel catalyst increase the oxygenation potential of a fossil fuel by removing the charge in molecular chains that cause hydrocarbon clusters. A fuel catalyst does not change the composition of the hydrocarbons. Instead, it removes the charge that binds hydrocarbons together in clusters thereby increasing the surface area of each hydrocarbon. By increasing the surface area of the hydrocarbons in an energy-dense fuel, a fuel catalyst increases the oxygenation potential of the fuel. 

Once diesel fuel passes through a fuel catalyst and enters the combustion chamber via the oxygenating fuel injectors, it combusts more completely. A more complete combustion means greater fuel efficiency and fewer toxic emissions.