Precision Combustion (United States)

Abstract Aviation jet engines often encounter anomalies in the fuel injector system that result in inefficiencies and lifetime reduction of the overall propulsion system. One of the primary causes of these anomalies is the thermal degradation of jet fuel when exposed to high temperatures at relevant engine conditions. This thermal decomposition can lead to the formation of carbon deposits that build up over time in atomizer passages, subsequently affecting injector spray patterns to the combustor and decreasing combustion efficiency. Hence, a “last chance” screen is used at the inlet of the injector to filter out unwanted solid particles from the degraded fuel. However, without proper maintenance a screen can experience deposit adhesion or fouling. To mitigate this issue, novel frangible-coated screens serve to slough-off deposits from surfaces by reducing the strength of adhesion forces. An experimental apparatus was developed to investigate the occurrence and causes of deposits on a screen. This tool also allows us to test coated screens that offer the ability to delay clogging of an injector. The apparatus simulates jet engine conditions in a controlled environment, allowing for the effect of flow rate, pressure, and temperature on fuel decomposition to be studied. This paper presents the results of coking experiments conducted over a realistic range of pressure and temperature and demonstrates the effectiveness of an advanced coating technology for mitigating carbon deposition.

Hydrogen (H2) is an important energy carrier for transitioning into a decarbonized economy. H2-producing membrane reactors (MRs), such as those used for fuel reforming or water-gas shift reactions, can enable low-cost blue H2 production from a variety of feedstocks, e.g., biomass, coal, or natural gas. This is a consequence of the enhanced feed utilization for the MR (i.e., kg·H2 produced per kg feed) compared to conventional multi-step H2 generation/purification schemes. Furthermore, H2 MRs simultaneously separate H2 and concentrate CO2, thereby increasing the overall process efficiency and facilitating pre-combustion carbon capture. This work describes an equation-oriented, technoeconomic optimization model for a water-gas shift membrane reactor (WGS-MR) integrated within a gasification process scheme with carbon capture to produce blue H2. We find using WGS-MRs, the levelized cost of H2 (LCOH) with carbon capture was estimated to decrease by ∼10% from $3.33 kg·H2−1 to $3.01 kg·H2−1 (2016 USD), compared to the baseline LCOH using conventional WGS reactors and pressure swing adsorption (PSA). Sensitivity analysis elucidates the influence of operating conditions (e.g., temperature, pressure, space velocity) on performance (i.e., CO conversion, H2 recovery) and identifies opportunities to further reduce the LCOH below $3 kg·H2−1. This study provides a blueprint for applying MRs in blue H2 production and motivates further studies on the optimal integration of these.

The primary focus of this paper was to examine the feasibility of using a solid oxide fuel cell (SOFC) generator (fueled with low sulfur liquid hydrocarbon) as the energy source for primary power of a small aircraft. Comparison with H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> -fueled, low temperature proton exchange membrane (PEM) fuel cells was also examined. A complete set of hybridized generators (SOFC + turbine + battery) system layouts were developed for short and long duration flights. Solid models and packaging concepts for the optimized SOFC solutions for both mission durations were also developed based on our prior testing data on the sub-scale.The work resulted in identifying key risks for scalability to mega-watt (MW) scale electrified aircraft propulsion (EAP). It can also be used to support certification and regulations development for electrified aircraft propulsion (EAP) systems in future work.

Lean premixed (LP) combustion is limited to a minimum NOx of 5–9 ppm due to flame stability. To improve flame stability and lower NOx, an advanced Rich Catalytic Lean-burn technology was developed and integrated to replace only the injector pilot with catalyst modules. This system focuses on replacing the highest temperature zone of the LP combustion system with a catalytic pilot (which can stabilize the main flame at reduced equivalence ratio) to reduce overall NOx emissions. This concept synergistically combines the best features of catalytic and aerodynamically stabilized combustion technologies. During Taurus 70 (T70) engine testing of a set of injectors equipped with catalyst modules for natural gas applications, emissions at baseload conditions were NOx of ∼ 2.5 ppmv and CO less than 2 ppm, both corrected to 15% O2. Low single digit emissions were achieved from 50% to 100% load. Combustor acoustics were low (below 0.1 psi/690 Pa) during testing. Reactor catalyst temperature was within the design limit and no-preburner was required. The initial emissions results are promising providing an alternative to conventional LP technology for less than 5 ppm NOx systems. Further development work is needed to establish engine integration and long term catalyst durability before advancing to production.

In order to meet DOE's goals of developing low-emissions coal-based power systems, PCI has further developed and adapted it's Rich-Catalytic Lean-burn (RCL{reg_sign}) catalytic reactor to a combustion system operating on syngas as a fuel. The technology offers ultra-low emissions without the cost of exhaust after-treatment, with high efficiency (avoidance of after-treatment losses and reduced diluent requirements), and with catalytically stabilized combustion which extends the lower Btu limit for syngas operation. Tests were performed in PCI's sub-scale high-pressure (10 atm) test rig, using a two-stage (catalytic then gas-phase) combustion process for syngas fuel. In this process, the first stage consists of a fuel-rich mixture reacting on a catalyst with final and excess combustion air used to cool the catalyst. The second stage is a gas-phase combustor, where the air used for cooling the catalyst mixes with the catalytic reactor effluent to provide for final gas-phase burnout and dilution to fuel-lean combustion products. During testing, operating with a simulated Tampa Electric's Polk Power Station syngas, the NOx emissions program goal of less than 0.03 lbs/MMBtu (6 ppm at 15% O{sub 2}) was met. NOx emissions were generally near 0.01 lbs/MMBtu (2 ppm at 15% O{sub 2}) (PCI's target) over a range on engine firing temperatures. In addition, low emissions were shown for alternative fuels including high hydrogen content refinery fuel gas and low BTU content Blast Furnace Gas (BFG). For the refinery fuel gas increased resistance to combustor flashback was achieved through preferential consumption of hydrogen in the catalytic bed. In the case of BFG, stable combustion for fuels as low as 88 BTU/ft{sup 3} was established and maintained without the need for using co-firing. This was achieved based on the upstream catalytic reaction delivering a hotter (and thus more reactive) product to the flame zone. The PCI catalytic reactor was also shown to be active in ammonia reduction in fuel allowing potential reductions in the burner NOx production. These reductions of NOx emissions and expanded alternative fuel capability make the rich catalytic combustor uniquely situated to provide reductions in capital costs through elimination of requirements for SCR, operating costs through reduction in need for NOx abating dilution, SCR operating costs, and need for co-firing fuels allowing use of lower value but more available fuels, and efficiency of an engine through reduction in dilution flows.

Sunpower, Inc., Yale University and Precision Combustion, Inc., are developing a wearable, JP-8 fueled, 35 We free-piston Stirling engine (FPSE)-based soldier power source with funding support from the DARPA Palm Power program and ARO. The new power source uses a Sunpower EE-35 FPSE, originally developed to convert heat from a radioisotope heat source into electrical power for NASA space probes during deep space missions. In this soldier power application the recuperative catalytic burner uses an electrospray technique developed by Yale University to atomize and deliver the JP-8 fuel to the catalyst. The combustion occurs on the surface of the special catalyst mesh which was developed by Precision Combustion, Inc. The catalytic combustor has been interfaced with the FPSE to achieve 42 We of power with a gross fuel-electric conversion efficiency of 22%. With design optimization and the use of off-the-shelf auxiliary components (pump, blower, igniter, start-up battery, etc.), 21% efficiency net of parasitic losses is achievable in a unit with a volume of 2.6 liters and a mass of 1.7 kg (excluding fuel tank) and with an energy density on the order of 1,000-2,000 Whr/kg (3.6-7.2 MJ/kg), a value one order of magnitude larger than conventional batteries. In Phase One of the program the team successfully demonstrated a breadboard version of the system which included all of the functional system components in a non-optimized, non-integrated package. In Phase Two of the program the team developed a compact integrated system which will be tested under representative field conditions in June 2006. This paper will review the progress made during Phase Two as well as the demonstrated performance of the current JP-8 fueled system.

Theoretical calculations have predicted that individual Single-Walled Carbon Nanotubes (SWNT) have extremely high thermal conductivity (around 6.6 × 104 W/m-K). The feasibility of constructing practical devices using the above mentioned properties, is critically dependent on the ability to synthesize high-thermal-conducting films. Highly conducting films would be of great use as heat sinks for the next generation of integrated chips. Excessive heating is currently a very serious problem in the endeavor for achieving faster and smaller chips. Since it is still not possible to perfectly align SWNT in the macroscopic scale, the thermal properties of the nano-films are therefore expected to have a statistical effect and thus lower than the intrinsic thermal conductivity of a single nanotube. Also the thermal conductivity perpendicular to the tube direction is more significant from a practical point of view. Multi-Walled Carbon Nanotubes (MWNT) were synthesized by Chemical Vapor Deposition (CVD) technique and subsequently characterized. The thin MWNT films were deposited by a solution casting technique over a metallic substrate. The off-axis thermal properties of these nano-films were studied by AC-calorimetry studies. In this method, the sample is heated by an AC source and the measurement of the relaxation rate is used to determine the thermal properties. This technique is well established for studying the thermal properties of complex fluids. Our results are contrasted with other thermal conductivity measurements intrinsic and bulk carbon nanotube samples. We have also measured off-axis thermal properties of nano-films synthesized from more crystalline SWNT samples and have compared this result with that of the MWNT-film. A model to explain the thermal conduction for our system is proposed.

&lt;div class="htmlview paragraph"&gt;The development of energy efficient, lightweight sorption systems for removal of environmental contaminants in space flight applications is an area of continuing interest to NASA. The current CO&lt;sub&gt;2&lt;/sub&gt; removal system on the International Space Station employs two pellet bed canisters of 5A molecular sieve that alternate between regeneration and sorption. A separate disposable charcoal bed removes trace contaminants.&lt;/div&gt; &lt;div class="htmlview paragraph"&gt;An alternative technology has been demonstrated using a sorption bed consisting of metal meshes coated with a sorbent, trademarked and patented [&lt;span class="xref"&gt;1&lt;/span&gt;] as Microlith&lt;sup&gt;®&lt;/sup&gt; by Precision Combustion, Inc. (PCI); these meshes have the potential for direct electrical heating for this application. This allows the bed to be regenerable via resistive heating and offers the potential for shorter regeneration times, reduced power requirement, and net energy savings vs. conventional systems. The capability of removing both CO&lt;sub&gt;2&lt;/sub&gt; and trace contaminants within the same bed has also been demonstrated. Thus, the need for a separate trace contaminant unit is eliminated resulting in an opportunity for significant weight savings. Unlike the charcoal bed, zeolites for trace contaminant removal are amenable to periodic regeneration. This paper describes the design and performance of a prototype sorber device for simultaneous CO&lt;sub&gt;2&lt;/sub&gt; and trace contaminant removal and its attendant weight and energy savings.&lt;/div&gt;