Fuel Catalysts Versus Diesel Oxidation Catalysts (DOC), Diesel Particulate Filters (DPF), and Selective Catalytic Reduction (SCR) Catalysts

Choosing a fuel or exhaust aftermarket device is a decision determined by the objectives of an owner/operator or corporation. There are only two objectives that pertain to fuel or exhaust aftermarket devices. With respect to aftermarket fuel and exhaust devices, the two objectives are either to improve the fuel efficiency of a vehicle or machine or to reduce its emissions.

Increasing the fuel efficiency of a vehicle or machine can also be the objective of purchasing aftermarket devices for diesel engines. Aftermarket fuel and exhaust devices also perform well on furnaces and boilers, extremely well in fact.

The problem with fuel and exhaust aftermarket devices is that there are similarities between each that make choosing the right one difficult. Add in the fact that there are fuel and exhaust conditioning additives and treatments marketed as catalysts make choosing the right product even more difficult.

Putting aside additives and treatments — which are solvents as opposed to mechanical devices — most fuel and exhaust aftermarket devices function in a similar manner. Adding to the complexity of purchasing the appropriate aftermarket device for your needs is the fact that high-quality exhaust and aftermarket devices are made of many of the same materials. Namely, diesel fuel catalysts and diesel exhaust after-treatment systems are devices which generate results as a consequence of the catalyzing properties of the noble metals used to manufacture them.

Similarities between Fuel Catalysts and Exhaust Aftermarket Devices (EAD)

One similarity between fuel catalysts and exhaust devices is that almost all fuel catalysts — with very few exceptions — are aftermarket devices. But unlike catalytic converters, car, truck and machine manufacturers are not mandated by law to install pre-combustion fuel catalysts on their products. Almost every passenger vehicle in the world has a catalytic converter or a diesel oxidation catalyst. That is not the case with inline fuel catalysts.

Like fuel catalysts — as the name implies — so too are exhaust aftermarket devices aftermarket products. In addition to the fact that both are aftermarket devices, both fuel catalysts and EADs are placed in direct contact with the particular fuel-state they are designed to affect.

Fuel catalysts mount on the fuel line. On the exhaust pipe following the exhaust manifold is where EADs are mounted.

Possibly even a greater source of confusion is the fact that — to the layman — fuel catalysts and EADs look almost exactly alike. The casings of both are either made of a noble metal like copper, stainless steel, or tin and are typically cylindrical. In addition to the fact that they are the same shape and made of the same materials on the outside, fuel catalysts and EADs are also made of the same materials on the inside: noble metals that are true catalysts.

Noble metals are the active agents that cause a change in the chemical composition of the respective fuel states they are designed to affect. In the case of a fuel catalyst, fuel. In the case of an exhaust aftermarket device, emissions.

Noble metals — true catalysts — and their arrangement within a catalyst or EAD constitute the “patent trade secrets” that make each device different.

The single greatest similarity between fuel catalyst and exhaust aftermarket devices, however, is the fact that both reduce emissions, though at different stages of diesel’s lifecycle. EADs, are post-combustion devices. Fuel catalysts are pre-combustion devices.

As the result of the fact that a fuel catalyst is a pre-combustion device, fuel catalysts can do something that neither exhaust aftermarket device nor catalytic converter can do: increase fuel efficiency.

To understand the difference between a fuel catalyst and diesel exhaust after-treatment systems, it is first necessary to determine what, exactly, each one is and does.

What is a Diesel Oxidation Catalysts (DOC)

A diesel oxidation catalyst is akin to a catalytic converter. Actually, they are almost synonymous. They have the same shape, components, and purpose. The difference, catalytic converters are mounted on spark-fired gasoline engines. Diesel oxidation catalysts, on the other hand, are mounted downstream of the exhaust manifold of a compression-fired diesel engine.

Simply, catalytic converters reduce gasoline emissions and DOCs reduce diesel emissions.

To understand the importance and purpose of DOCs, it is necessary to understand the limitations of engines powered by fossil fuels. Because of a variety of factors including the nature of refined fossil fuels; engine compression ratios and spark-fired engine timing; ambient temperatures; and elevation and air pressure, no engine burns 100 percent of the fossil fuel that enters its combustion chambers. As a result, fuel hydrocarbons escape into the atmosphere as emissions pollution.

The purpose of both catalytic converters and diesel oxidation catalysts is to minimize the amount of unburned fuel that escapes into the atmosphere. Catalytic converters and DOCs finish the combustion process by super-heating the exhaust of a vehicle or machine using noble metals — true catalysts.

Diesel oxidation catalysts, “contain palladium, platinum, and aluminum oxide, all of which serve as catalysts to oxidize the hydrocarbons and carbon monoxide with oxygen to form carbon dioxide and water.” DOCs are cylindrical flow-through filters with honeycomb screens on the interior. Diesel emissions pass through the screens. The unburned fuel molecules in the emissions combust and become carbon dioxide or water.

And what superheats the noble metals in a diesel oxidation catalyst so they can combust the unburned fuel in the exhaust? Exhaust. A diesel oxidation catalyst has a symbiotic relationship with the exhaust it cleans. The exhaust passing through the DOC heats the noble metals and the noble metals then combust the unburned fuel molecules — the hydrocarbons — in the exhaust that follows.

What is a Diesel Particulate Filter (DPF)

In addition to unburned fuel — which escapes the engine in the form of gas or vapor, — diesel engine emissions contain particulate matter, solids. Particulate matters, the solids, are visible to the naked eye. Particulate matter is often called soot.

Particulate matter is the cause of the black smoke that is sometimes visible from diesel engines, boilers, and furnaces. Particulate matter is the cause of smog, the brown cloud that often hangs over the cities of industrialized countries.

Particulate matter consists of primarily three components. The three elements of particulate matter are a soluble organic fraction (SOF), fuel derived hydrocarbon (FHC) and lubricating oil hydrocarbon (LHC). Because of low sulfur diesel fuel is a distribution requisite in much of the first world, particulate matter in the atmosphere has dropped dramatically around the globe.

However, no diesel is sulfur free. And, there are still large sums of particulate matter as a result of hydrocarbons as well. But fortunately, particulate matter is a solid — as opposed to a gas or vapor — which means filters can remove particulate matter from diesel fuel emissions. And, that is what a diesel particulate filter does. In the same manner, a DOC combusts unburned fuel; a DPF removes the solids from diesel combustion emissions.

A diesel particulate filter is very similar to a fuel filter. A fuel filter removes the solid debris found in fossil fuels before combustion. A diesel particulate filter cleans the solids out of engine exhaust prior to it escaping into the atmosphere. “This matrix of materials (a composite of cordierite, silicon carbide, or metal fibers), called a diesel particulate filter (DPF), traps the particulates (soot) flowing out the exhaust pipe.”

Typically, when a diesel particulate filter is used in conjunction with a diesel oxidation catalyst, the DOC is next to the exhaust manifold and the DPF is a few feet down the exhaust pipe. The third emissions device that can be used on an exhaust system is a selective catalytic reduction catalyst.

What is a Selective Catalytic Reduction (SCR) Catalyst

Some of the most toxic emissions that escape into the atmosphere following the combustion of fossil fuels are oxides of nitrogen. Nitrogen oxides are a danger to not only people but almost all living creatures. “The chief concern is how the small particles are able to damage our lungs by entering into sensitive tissue areas. This has terrible consequences and can lead to premature death, respiratory ailments and diseases, and can even contribute to heart disease.”

But that’s not all. Nitrogen oxides have the ability to create chemical changes and a large number and wide variety of different compounds. Many of the consequences of the chemical compounds are not yet known. Furthermore, it is not easy to determine when or where nitrogen oxides will create a chemical change in an otherwise innocuous compound.

“NOx continually changes many common organic chemicals which end up creating numerous toxic products such as nitroarenes nitrosamines and nitrate radicals. These toxic products can often cause biological mutations in many life forms that were unfortunate enough to be exposed to it.

Other odd means for NOx to transform into Ozone are being discovered, the most recent being the formation of Nitryl Chloride which occurs in many coastal areas when NOx comes into contact with salt mist sprayed by crashing waves.”

Selective catalytic reduction catalysts turn oxides of nitrogen into benign chemical compounds.

Fuel Additives and Treatments

Though often labeled catalysts, fuel additives, and treatments are not catalysts nor do they contain catalysts. Fuel additives and treatments do not create a chemical change in fuel nor do they improve fuel the fuel itself in any manner.

Fuel additives and treatments serve one of three purposes or a combination of them. Additives and treatments can lubricate an engine, they can remove the hydrocarbon residues that foul internal combustion components of an engine or they increase the cetane/octane of a fuel.

What is a Fuel Catalyst

Unfortunately, the term fuel catalyst is thrown around and used to label a variety of different products including additives and treatments. A true fuel catalyst, however, is a pre-combustion device that conditions fuel in order to minimize the gap between diesel fuel energy potential and diesel fuel energy output. What separates a fuel catalyst from pseudo-fuel catalysts is the fact that true catalysts — noble metals — are the active agents in a fuel catalyst that produce a chemical reaction.

The other feature of a fuel catalyst that separates it from catalytic converters and other emissions-reducing mechanical devices as well as fuel additives and treatments is that fuel catalysts not only reduce emissions but increase fuel economy — “gas” mileage.

Unlike almost every other aftermarket addition, a fuel catalyst both increases fuel economy and reduces emissions.

With respect to emissions reduction, diesel fuel catalysts can reduce emissions by unparalleled sums. For example, the Rentar Fuel Catalyst decreases particulate matter — arguably the biggest drawback of diesel fuel combustion — by 19.2 percent. Black smoke reductions from the Rentar can reach up to 44 percent. The Rentar reduces elemental and organic carbons by up to 35 percent. It reduces cancer-causing volatile organics by between 16 and 46.2 percent, depending on the volatile organic in question.

With respect to diesel fuel catalysts versus diesel exhaust after-treatment systems, there are vast differences. But, the two biggest differences are what the purpose is — recondition fuel or recondition emissions — and the fact that fuel catalysts increase “gas” mileage while diesel exhaust after-treatment systems increase fuel consumption.