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SNARRE technology is an advanced scrubber system designed to reduce NOx and PM exhaust emissions. By design, SNARRE also reduces fuel consumption and greenhouse gas emissions. To understand how it works, how it differs from current scrubber technology and how it is inherently better, a history lesson about the evolution of NOx scrubbers may be enlightening.


Regulatory agencies such as the EPA, EU and IMO restrict the number of nitrogen oxides (NOx) and particulate matter (PM) which can be released by internal combustion engines. The allowable pollution levels have been ratcheted down over time, forcing engine manufacturers to continually develop newer, less polluting engines. Eventually, the pollution requirements dropped below what the engines were capable of achieving on their own. For diesel and natural gas engines, this meant the exhaust coming out of the engine would have to be scrubbed or treated with an exhaust aftertreatment system.

The first regulatory requirements that necessitated a dedicated NOx treatment system on vehicles was Euro Stage IV. This went into effect in 2005. At that time, aftertreatment systems were not a new concept. NOx had been a problematic byproduct of fuel combustion from power generation plants and factories, causing large-scale acid rain in Europe and around the world. Scrubber systems were first developed to combat this problem. One such system was built around Selective Catalytic Reduction technology (SCR). SCR systems convert the NOx created during combustion back to atmospheric nitrogen with the use of a gaseous, hydrogen-bearing reductant and a catalyst chamber. The hydrogen source of choice was urea, a chemical compound that could be dissolved in water and injected into the exhaust stream. The urea breaks down into an ammonia gas, which in turn reacts with the NOx in a catalyst chamber creating nitrogen, water and carbon dioxide. The first stationary SCR system was used on a Japanese power plant in the 1970s. By the mid 1980s, SCR systems were common-place throughout Europe.

The first mobile applications requiring NOx reduction systems were aboard large ocean vessels. The first two systems were installed on a pair of Korean cargo ships beginning in 1989. These were mobile adaptions of the systems first developed for stationary applications. Passenger vessels and other large marine applications soon followed.


Automaker Involvement

By 2005, Euro Stage IV necessitated the use of aftertreatment systems in the European on-road market. Automakers and engine manufacturers looked to the large-scale, stationary and marine systems for inspiration. They successfully miniaturized the catalyst, mixing and dosing systems. The big innovation that arose was packaged liquid urea, now known by such trade names as DEF and AdBlue. Nissan was the first to market in 2004, using SCR systems on the Quon heavy-duty truck.

Although the technology was a breakthrough at the time and greatly reduced NOx emissions from vehicles, the systems added considerable complexity to engines and vehicles.  A separate tank was required to store the urea exhaust fluid. Additional pumps and special injection nozzles and mixing chambers became necessary. The slippery and corrosive fluid was prone to leak. Since the liquefied urea was 66% water, it would freeze and become inert or deteriorate when heated. The catalysts act like an oven and have to be heated to a certain temperature for the ammonia to properly react with the NOx. This was an issue in idling engines. The exhaust temperatures were not hot enough, so the engines had to be modified to dump additional fuel into the exhaust in order to increase the catalyst temperatures. It was ironic. In order to lower pollution levels, the engines actually became less fuel-efficient, emitting more CO2 greenhouse gasses. This is true to this day.

The variable speed, load, and RPM of automotive engines also posed a new problem. Power plants and large marine engines run at fixed speeds, emitting a steady stream of exhaust. Any changes are gradual and easily predicted. Automobile engines vary in load and speed and RPM constantly and often quite suddenly. The aftertreatment systems could not react fast enough. This resulted in two problems. If there wasn’t precisely enough ammonia to react with the fast moving NOx in the exhaust, too much NOx would “slip” by, creating excessive pollution. If too much ammonia was present, the opposite would happen and ammonia slip would occur, releasing toxic levels of ammonia gas. To correct this problem, sophisticated urea dosing controllers were developed. The controls had to be integrated into the engine onboard governing computers which regulated the amount of fuel being delivered to the engine. By reading the varying amount of fuel going in, the dosing system could “predict” how much exhaust gas would soon be created and vary the amount of urea being injected accordingly.


Aftertreatment Comes to America

These mobile systems became the standard approach to meet EU automotive and off-road emissions requirements. By 2010, emissions standards in the US would require American engine manufacturers to develop aftertreatment systems. In the early 2000s, General Motors tasked a team of physicists, chemists, and engineers to begin the development of a NOx scrubber system at their subsidiary, Delphi.

The team recognized the complexity and inherent shortcomings of the mobile SCR systems and decided to start fresh; they started with the chemistry. To convert NOx back to nitrogen requires hydrogen. The hydrogen steals the oxygen from the NOx, creating water, and forcing the NOx back to what was going into the engine, harmless atmospheric nitrogen. They asked themselves, why use urea? It is difficult to store, and every molecule of urea only has 4 hydrogen atoms. That’s relatively few when compared to hydrocarbons. Hydrocarbons, aka the fuel in the gas tank, are laden with hydrogen. After all, it’s the hydrogen in the fuel that is the actual energy source. Every molecule of diesel fuel has on average 24 hydrogen atoms, 6x that of urea.

With that in mind, the team set out to create a fuel reformer that could efficiently reform fuel into hydrogen. They were successful. The reformer was then paired with a NOx absorbing catalyst.  Absorber cats have a special metal substrate which acts like a NOx sponge. The exhaust gas flows through the cat, and the substrate chemically traps the NOx as it goes. In their tests, a slow but steady stream of hydrogen from the fuel reformer and into the cat converted the NOx back to nitrogen.

The concept was proven and the team began work to develop an exhaust system around their technology. Unfortunately, the team didn’t get much further than that. Saddled with over 100,000 United Autoworker Union pension plans by their parent company, Delphi was intentionally torpedoed. This was 2005, the beginning of the great recession, and the bankruptcy of the American automotive industry. Delphi was dismantled, the buildings bulldozed, and all the employees let go.

The ambitions to create the next generation of emissions technology were dashed, and the project mothballed forever. GM took an abrupt about face and decided to take a less ambitious approach and just adopt the mobile SCR systems being used in Europe. Somewhere in the process, it was ironically decided to use the reformer technology to make urea, to fuel the very SCR systems the reformer was designed to replace. Eventually, and maybe thankfully, that idea was abandoned as well. To this day, SCR is the de rigueur technology of the land, adopted by almost every major engine manufacturer, fueling a 22 billion dollar global urea industry.


Innovation Persists

Fortunately, the story didn’t end there. A lead physicist and engineer at Delphi by the name of Mark Hemingway would not let it go. Mark’s entire career had been in the American automotive industry. He had put his heart and soul into what he thought would be his lasting contribution to American manufacturing. Mark persisted on his own, refining the technology, simplifying the dosing systems, redesigning the reformer from the ground up over and over to improve the hydrogen yield. A big breakthrough came with the addition of a second adsorber and a valve to switch the exhaust gas flow back and forth between the two. NOx sensors were positioned at the inlets and outlets of the adsorbers, tracking the flow in and out. Mark designed and built a controller with a learning algorithm to track the flow and control the hydrogen production. What started as a proof of concept at Delphi, one guy, in his garage, turned into a complete and working prototype. This was the birth of what we now call SNARRE, Switched NOx Adsorber & Reformer Regenerated Exhaust.

Hemingway’s end result was light years beyond what had begun at Delphi, radically different from where it had begun, and far beyond the outdated SCR systems that came before. His switched adsorber system ran independently of the engine, didn’t require a separate exhaust fluid and operated efficiently at half the temperature of SCR systems, not needing any additional fuel to stay hot. Because it had entirely different operating principles, it wasn’t subject to the NOx or ammonia slip of the SCR systems and operated on ½ of 1% of the engine’s fuel consumption. SCR systems consume on average 5% of an engine’s fuel consumption in urea, on top of the additional fuel burned to maintain catalyst temperature. In short, he had developed the elegant solution for NOx reduction the world needs.



Freeboard Sound Solutions was built to realize the disruptive potential of this technology in the marine market and beyond. For better or worse, diesel engines won’t be replaced with new technology on most vessels for a decade or more. The SNARRE exhaust system can be used on engines old and new to reduce pollution harmful to human health and greenhouse gas. It’s simpler, more economical, smaller and less costly to incorporate into ships and equipment than the current SCR systems being used today. To learn more about where we plan to enter the market, who our target customers are, and how we plan to scale, visit our Strategy page.