University Focus – Valence | Engine and powertrain technology International
Could a team of researchers from Valencia turn the tide of the combustion engine with a system that promises to produce zero NO?X and capture all of its CO2 production?
It’s easy to see why the internal combustion engine has dominated the automotive market for so long. With energy-dense liquid fuels, widely available raw materials, and a mature global infrastructure in place, it is hard to imagine the industry moving away from this technology if the crucial issue of tailpipe emissions could be addressed. . And a team of Spanish researchers claim to have done just that.
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Led by the CMT-Motores TÃ©rmicos (CMT) group of the Polytechnic University of Valencia and the Spanish Institute of Chemical Technology (ITQ), the project combines CO2 capture and oxycombustion to produce an engine that emits neither COâ nor NOX and very low levels of non-engine particulate matter.
The concept is based on a technology developed at ITQ that uses ceramic structures known as mixed ion and electron conductive membranes (MIEC) to separate gases. This allows the intake air to be filtered for near pure oxygen, thereby eliminating the potential for NO formation.X. Plus, it frees the powertrain engineers from NOX/ particle compromise that comes with conventional combustion. The small amount of particulate matter that remains is captured with the COâ rather than released into the atmosphere.
âThis technology works both for spark ignition [SI] and compression ignition [CI] engines â, explains Dr JosÃ© Serrano, professor at CMT. âIn both cases, we have been able to reduce particulates to virtually zero and CO emissions well below a state-of-the-art engine. The exhaust gases are mainly COâ and water. There are also hydrocarbons, but we oxidize them in a simple catalyst. “
Another advantage of this process is that the resulting COâ is about 95% pure, which simplifies the task of capturing it. This is done by compressing the exhaust gases to the critical point where they liquefy. A condenser is used to remove the water vapor beforehand and a pump maintains the flow through the exhaust.
There are a variety of potential approaches to compressing COâ itself, but the idea put forward by Serrano and his colleagues is to adapt one of the engine’s cylinders to act as a compressor. âWe believe that it would be possible to adapt this system to an existing engine using this principle,â notes the professor.
This would result in a carbon neutral engine when running on fossil fuels. But perhaps the most exciting prospect is that of combining the engine with synthetic fuels.
âIf you run the engine on synthetic fuels, you can actually run with negative emissions, so the vehicle would actively remove COâ from the atmosphere,â notes Serrano. âWe can see a dollar value in this, with manufacturers receiving COâ credits, and the COâ itself has value once it’s captured and compressed. “
As anyone who has ever used an oxyacetylene torch can attest, burning fuel in pure oxygen can lead to extremely high temperatures. To prevent this, the engine returns a significant portion of the COâ and water vapor – 60 to 70% – back to the cylinder in the form of EGR.
âThe conditions in the cylinder are similar to those of a current peak production engine,â comments Serrano. âThe maximum temperature is around 1,000 Â° C at full load and the maximum pressure is around 180 bar. We can also use a lot of conventional technology. For example, the fuel injection material is completely unchanged; the geometry of the combustion chamber can be optimized, but this is not radically different. The only totally new thing is IMCS, but the technology is quite similar to a DPF, so it’s something OEMs are already familiar with.
Serrano says there is potential to establish a circular economy around COâ, with liquefied gas traded at gas stations when the vehicle is refueled. The relatively high purity of the COâ produced by this process means that it can be directly fed back into a variety of industrial processes, including the production of synthetic fuels.
These are ambitious goals, but Serrano points out that oxy-combustion and COâ recovery are two technologies already in use in industry. The team’s initial project successfully demonstrated the combustion side of the process in two working prototypes – a single-cylinder SI engine and a four-cylinder CI engine – leading to an international patent. A second project supported by the Valencian Innovation Agency should start soon, focusing on the COâ capture component.
“For me the most important discovery to come from this work is that we have demonstrated zero NOXemissions, both theoretically and experimentally, and still maintained the BSFC [brake-specific fuel consumption] of a conventional engine, âcomments Serrano. “And the high purity of COâ shows the potential for zero emissions from tank to wheel.”
With careful management, the oxycombustion process would greatly increase the knock limit in an SI engine. It also reduces trapped mass, allowing the compression ratio to be increased without exceeding the maximum pressure limits in the cylinders in an IC engine. As a result, the team was able to increase the compression ratios from 11: 1 to 22: 1 on the SI engine and from 16.2: 1 to 28: 1 on the CI engine.
This allowed an increase in maximum torque from 410 Nm at 2000 rpm to 560 Nm at 1600 rpm for the CI engine. Peak horsepower dropped slightly from 172 ps to 160 ps, ââbut the BSFC at 2,500 rpm went from 211 g / kWh to 219 g / kWh.
Transporting your own chemical processing plant is not without its challenges, although there is a parallel here with existing after-treatment systems, which the automotive industry has become very adept at producing and managing. At present, the additional hardware for the oxy-fuel system occupies roughly the same space as the engine itself.
It is not said that the planned COâ capture system will significantly increase the overall footprint if it uses one of the existing cylinders, and its power consumption is expected to be 10% of braking power. Storage should always be considered, with each fuel tank releasing around three times the volume of COâ, but Serrano is confident the system can be reduced for real applications.
âInitially, we see this technology being used in long haul trucks, ships and locomotives because it’s a fairly large system,â he says. âPacking is obviously easier on a large ship, and when they get back to port they have the infrastructure there to offload the COâ. Many refineries where synthetic fuels are produced are already based in ports due to the logistics of transporting crude oil. “
Serrano also believes the potential is there to use the system for automotive applications: âWith the exception of a basic oxidation catalyst, you don’t need any conventional aftertreatment system, which will free up space and offset the costs. Ultimately we can see this being used in passenger cars – perhaps not as the sole engine, but as part of a hybrid system or range extender with zero tailpipe emissions.
Discussions have already taken place with a well-known truck manufacturer. Work has started on the carbon capture system for the next phase of the project, and the team is aiming for a tight schedule.
âWe hope to have fully tested TRL 8 technology covering both oxy-combustion and COâ capture by the end of next year,â Serrano says. âIt will then be a question of costs, opportunities and regulations. Being optimistic, I think we might see a utility vehicle with this technology in three years.
There are still challenges to overcome, but this project raises the tantalizing prospect of zero-emission propulsion from conventional liquid fuels. This is another reason to wonder if the demise of the internal combustion engine is as imminent as some would have us believe.