AN INTERNAL COMBUSTION ENGINE WITH CO2 CAPTURE
Wilson Hago, Ph.D. Andre Morin Efficient Hydrogen Motors www.efficientyhydrogenmotors.com
ABSTRACT
Increasing world-wide carbon dioxide emissions from various sources threaten the living standards of billions of people as well as the ecological stability of animal and plant life on the planet. As countries realize the seriousness of the problem, they will be forced to impose more stringent measures to reduce carbon dioxide emissions. This proposal aims to mitigate coming measures via the design of a motor engine that reverses ambient carbon dioxide during its operation. This is achieved by an integrated hybrid system comprised of a novel hydrogen-burning motor engine, a battery, a turbo-generator, and an apparatus that captures carbon dioxide from the atmosphere. As the exhaust gas comprises water, the use of this system leads to negative carbon emissions. Various stages are necessary before this envisaged engine becomes reality. The first stage comprises the production of a prototype that works in a virtual environment. The prototype should be mechanically sound and show robustness when tested against vibrations, temperature distributions and stresses. The goal is then to leverage the functional virtual prototype to produce a functional physical prototype.
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Index
1.
Abstract
2
2.
Introduction and background
4
3.
Economic Justification for CO2 capture
4
4.
Feasibility of CO2 capture in automobiles
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5.
Base Engine
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6.
Carbon Dioxide Removal System
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7.
References
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INTRODUCTION AND BACKGROUND Severe global consequences are predicted for the continual production of carbon dioxide from industrial and automobile sources. Ocean levels are predicted to rise during the next several decades, bringing unwelcome global dislocations to billions of people. Rising global temperatures are expected to lead to extreme weather events, ozone depletion, animal and plant extinctions and more pronounced spread of diseases. Driving much of this warming are hydrocarbon emissions from automobile sources.
Our proposal aims to address this problem directly via the design of an engine that removes carbon dioxide from the atmosphere.
To our knowledge no comparable
engine design presently exists to reverse global carbon dioxide emissions.
Anthropogenic carbon emissions have been rising dramatically since the start of the Industrial Revolution circa 1750. Present worldwide carbon dioxide emissions are 30 G tons/year and are expected to rise as China and India become more industrialized. Carbon dioxide levels have remained below 900 ppm for the past 60 million years and below 350 ppm for the past 25 million years [1-3]. Present CO2 levels are 390 ppm and are rising 1-2 ppm every year [4]. Some scenarios call for planetary carbon dioxide levels reaching 1000 ppm by the year 2100. Recent data indicates that we are on a trajectory that follows this worst case scenario. These levels would be outside the range of mammalian evolution. Indeed, at 600 ppm some people report the air to be stuffy. It is prudent for us to take steps to maintain CO2 levels at levels consistent with our history. Accordingly, this project presents a proposal to reduce atmospheric carbon dioxide levels via the use of an internal combustion engine that captures carbon dioxide.
ECONOMIC JUSTIFICATION FOR CO2 CAPTURE Presently, only a few countries have enacted measures to combat carbon emissions. There are basically two strategies: carbon taxes and cap and trade measures. Of the former, the Scandinavian countries have led the way since the 1990’s in enacting carbon taxes. Presently, Sweden, Finland, Denmark and Norway have enacted taxes 4
ranging from $40 to $17/ton CO2. France recently almost passed a carbon tax, but political opposition overcame the proposal. In the Americas, there are no country wide taxes, though certain cities have taken the initiative to enact taxes. Boulder, Colorado has one charging $3/ton and British Columbia has one at $5/tonCO2. We believe that as countries realize the seriousness of rising global carbon dioxide levels, more carbon emissions measures will be enacted. Indeed, we predict that carbon taxes are likely to be enacted throughout all the major countries in the world, and that present taxation levels will rise significantly as countries realize they need to significantly influence people’s consumption behaviors. Companies that can avoid paying carbon taxes by buying cars with CO2 capture devices will do so, as long as the cost of capturing CO2 makes economic sense.
FEASIBILITY CO2 CAPTURE IN AUTOMOBILES
Various ideas have already been proposed for the capture of CO2 from the atmosphere. Lackner has proposed building large towers with areas of 50 to 60 m2 and bringing air to pass through the towers [5]. The towers contain a large surface area sorbent that binds CO2 from ambient air. Air exits with a lower concentration of CO2. These ideas have in common passing large amounts of air through a sorbent and then regenerating the sorbent. The basic idea of our project is that automobiles, by virtue of their operation, encounter a large amount of air. Instead of using enormous windmills as have been proposed by some, it is better to consider an automobile as a mobile windmill and use it as the air collection device. Consider an automobile that travels an average speed of 40 mph (20 m/sec) and assume it exposes an effective capture area of 1 m2.
If one installs a
device with sorbent capture rate of 150 micromoles/m2/sec (present technology), one automobile could capture 11 kg CO2 per day. If every automobile in the United States were to have one of these capture devices, this would represent a removal of 800 5
million tons of CO2 from the atmosphere. This is 15% of present yearly US automobile yearly CO2 emissions and 5% of world yearly CO2 emisssions. This is a significant fraction in just one year. We believe CO2 reversal would work best with automobiles that burn fuels that produce carbon emissions. In this manner we will have a true reversal, instead of a displacement of carbon production to somewhere else. The best fuel to use is hydrogen, since it can be readily obtained from the electrolysis of water. The energy for the electrolysis could be obtained from carbon burning sources such as coal and natural gas, as long as they are tied to carbon capture and sequestration (CCS) processes. Energy may someday be entirely derived from non-carbon burning sources such as solar, wind, geothermal, and nuclear. The basic ideas at Efficient Hydrogen Motors are as follows: 1) Develop an air cooled hydrogen combustion engine that captures CO2 during its operation 2) Have the CO2 capture energy come from normal operation and waste heat 3) Build a prototype engine and 4) License the idea to an OEM to manufacture. The rationale behind an air cooled engine is to replace the liquid cooling system with a CO2 capture device. Instead of having a radiator where liquid coolant flows, we intend to have a grid open to air and through which hydroxide circulates.
BASE ENGINE The base of our air cooled design is a 5-cylinder radial engine with 4-strokes, but modified to cool the internal chambers. Radial engines have been in use since the turn of the century, primarily in the aviation field, where they have served as engines for a variety of airplanes, from light airplanes to heavy carriers such as the Constellation. The advantages of radials is that they are light, have a high HP/weight ratio, and produce good torque compared to similar size and HP 4-stroke internal combustion engines. Fuel consumption is fairly good too. Rotec Engineering, a company based in Australia, 6
manufactures a 7-cylinder radial 110 HP air cooled engine that weighs 100 kg and has a fuel consumption of 200 g/kWh at 80% power. A comparable Audi A4 1.9L TDI engine having 115 HP has a fuel consumption of 220g/kWh at 80% power. The latter is an engine that gets 50 mpg and is about as efficient as Toyota Prius engine 1.8L engine.[6] The disadvantages of using radials are the strong stresses experienced by the crankshaft and extra vibrations. Both of these disadvantages may be dealt by proper engineering. The combustion of hydrogen in an internal combustion engine differs in several respects from the combustion of gasoline or diesel in an internal combustion engine (ICE). The minimum ignition energy of hydrogen is an order magnitude lower than that of gasoline[7]. This fact has particular consequences in hydrogen preignition and severe engine knocking if hydrogen is used in unmodified ICEs.
The wide flammability range
of a hydrogen-air mixture (4-76% air) also contributes to the preignition problem. The flame velocity of hydrogen is approximately 7 times that of gasoline [8], which leads to excessive forces on the crankshaft. The high diffusion of hydrogen in air (an order of magnitude higher than gasoline in air) leads to unburned hydrogen escaping into the crankcase unless it is combusted at top dead center. The quenching distance is smaller than gasoline, a fact leading to higher heat transport to chamber walls. There are other issues that also need to be addressed, such as the need for special piston ring lubricating agents, hydrogen-induced metal embrittlement, and NOx control. While it is true that at present there is no widescale infrastructure for the utilization of hydrogen in automobiles, we believe this situation will change with impending significant increases in gasoline costs. Global consumption of gasoline keeps increasing while conventional supplies have not grown, taking into account depletion of present reserves. Production of hydrogen from cheap electricity from renewable sources will likely be the norm rather the exception in the future. It is our estimate that at a price above $200 a barrel of oil, we will start to see significant attention paid to hydrogen. Plug-in hybrid automobiles are likely to dominate the landscape in the near term future, but their limited range means that a portable fuel is still needed. 7
We believe the hydrogen burning radial we have designed has high efficiency because it follows closely the ideal Otto cycle. In the ideal Otto cycle, adiabatic compression and expansion are accompanied by constant volume combustion and heat rejection processes (Fig. 1). EHM engine takes advantage of the high flame speed of hydrogen by having a direct force transmission to the piston during the power stroke which forces the piston to move down quickly without encountering drag as in a gasoline engine. This is accomplished via a crankshaft with a crankpin that moves linearly during its descent during the power stroke. (Fig. 2). In a typical gasoline or diesel engine the crankpin executes a circular motion during its descent.
Figure 1. Ideal Otto cycle
Figure 2. Linear crankpin descent during power stroke 8
Additionally, the EHM engine is particularly adapted to hydrogen combustion because it exhibits effective cooling of interior (as well as exterior) chambers. This is important to avoid any hot spots which would lead to preignition events. Effective cooling is achieved via a design that utilizes an additional cylindrical structure within the cylinder. This cylinder structure, denoted as a sleeve (see Fig. 3a) separates the piston from the cylinder and has three orifices whose purpose is to serve as a mechanical valve that controls the flow of exhaust air out and flow of fresh air into combustion chamber. The orifices comprise two exhaust ports and one intake port. The outermost cylinder with fins also possesses similar three orifices. The sleeve separates two chambers, the combustion chamber below it and the hydrogen injection chamber above it. There is a valve on top of the cylinder that controls delivery of hydrogen to the hydrogen injection chamber. During the power stroke a stoichiometric mixture of hydrogen and air is spark ignited. The piston descends below the bottom orifice and this starts the cooling phase as air is sucked out through this orifice. As the piston ascends, the sleeve descends, aligning the orifices leading to the exterior, and fresh air is forced in via the supercharger for further cooling (see Fig. 3b). In this manner the interior combustion chamber is quickly cooled.
Fig. 3a,3b. Illustration of cooling of interior chamber in EHM engine. 9
Based on the formula for efficiency for an engine that follows an ideal Otto cycle,
Where V1= volume at bottom dead center and V2= volume at top dead center and γ=CP/CV=1.4 for H2. For our engine with a compression ratio V1/V2= 10 we obtain a theoretical efficiency of 60%. Temperature at top dead center after compression is calculated to be 400°C. Directly attached to the engine is a device that is a combination of a centrifugal supercharger, turbocharger and generator. This device is mechanically connected to the crankshaft during idle and draws in fresh air and sends it to the intake manifold (see Fig. 4). At higher speed the device disengages from the crankshaft at which point the fresh air supply is propelled by an exhaust-driven turbo. At the end of the shaft of the turbogenerator are magnetic poles that serve to generate current during the normal operation of the supercharger/turbogenerator. The generated electricity will power the CO2 capture assembly. The engine as depicted is expected to have a 90 cm diameter and 50cm thickness (without turbo assembly). It is designed for 200 HP and 450 lb-ft torque with a weight of 150 kg. A CAD simulation of engine is shown in Fig. 5. The reader should click on the engine to see the movement.
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Fig. 4 Engine with supercharger/turbocharger attached.
Actual CAD simulation
Fig. 5 Simulation of Engine Movement. Please click on figure to see simulation. 11
CARBON DIOXIDE REMOVAL SYSTEM The removal of carbon dioxide is accomplished via the reaction of ambient CO2 with aqueous base circulated in CO2 scrubber columns. It is well known that alkali base is an efficient scrubber of CO2. In our design the aqueous base is carried on board. The relevant reactions are: 2NaOH + CO2 Na2CO3 + H2O
ΔH° 298K= -128 kJ/mol
NaOH + CO2 NaHCO3
ΔH° 298K= -132 kJ/mol
The reactions could work with any cations from group I (for example Li+, Na+, K+), group II, group III, transition metals, or ammonia containing cations, such as NH4+., but Na+ is the most economical. The resulting carbonate ions are fairly soluble in the alkali solution. The idea is to exchange the carbonate-laden solution at the ‘gas’ station with fresh NaOH. The carbonate-laden solution would be treated off-site where it would be dried and the carbonate heated to regenerate the CO2 per the following equation: Na2CO3 CO2 + Na2O
(860°C)
The resulting sodium oxide from the decomposition could be reacted with water to regenerate the sodium hydroxide per the following reaction: Na2O + H2O 2NaOH A variation of this process is the Kraft Process, in which calcium hydroxide is reacted with the sodium carbonate to render the more insoluble calcium carbonate: Ca(OH)2 + Na2CO3 CaCO3 + 2NaOH The initial decomposition temperature of the calcium carbonate is similar to the sodium carbonate. A cost and energy analysis of the Kraft process applied to capture of CO2 from air was performed by Baciocchi et al [8]. They calculated a thermal energy cost of 6GJ/ton CO2 12
with most of the energy coming from the decomposition of the calcium carbonate. If this energy were to be obtained from electricity costing $0.08/kWh then the process cost translates to $134/ton CO2. This is certainly above what any country has presently imposed for carbon taxes. However, it is possible that the energy for calcination maybe derived directly from thermal energy from concentrated solar energy or other passive solar process, in which case costs would be a fraction of the electricity derived cost. At any rate we expect carbon taxes to rise precipitously as countries realize the seriousness of the problems created by carbon emissions. The best known CO2 capture approach involves the use of structured packing towers. In these structures, a high surface area ceramic serves as the means to increase contact between the liquid NaOH solution and the incoming CO2. Typical capture rates are 150 micromoles/m2 /sec for 2M NaOH at an air speed of 2m/sec.[8] Larger surface areas approaches include the use of spray towers [9] and the use of falling films [10]. These two methods significantly increase the capture rate, but these methods have been tested with air speeds considerably less than 2m/sec. As mentioned previously, a method is desired that can process air with speeds exceeding 20 m/sec. EHM intends to use a variation of the scrubber shown in Fig. 6 in its design. This was a device originally built by Margaria [11] to capture CO2 from the breaths of individuals exercising on treadmills. The device pumps NaOH through a high surface area Rashing rings. Within these rings the NaOH encounters relatively high speed air moving in the opposite direction.
The carbonate-laden solution is pumped to a NaOH compartment
that is separated from the NaOH reservoir by a siphon. The siphon serves to resist air going directly to the NaOH reservoir. It is expected that the air entry is a square of dimensions 10 cm x 10 cm. One hundred of these units are expected to be placed in the frontal area of the automobile. In this manner 1 m2 of frontal area will be exposed to incoming air. This arrangement is expected to cause increased overall automobile air resistance, but the higher engine efficiency should compensate for this decrease. As mentioned previously, the pump energy is expected to be derived from waste heat via the use of a turbogenerator. It is expected that once a given level of carbonate is 13
attained in the solution, as determined for example by conductivity readings, air passage through the CO2 capture device would be bypassed.
Fig. 6. EHM CO2 scrubber Once the CO2 is released from the carbonate off-site, it is expected that it will be sequestered. Carbon dioxide sequestration is a well known technique used presently by a variety of companies to bury the CO2 and avoid paying CO2 taxes. The sequestration involves injecting compressed CO2 into an abandoned oil reservoir or aquifer in supercritical form. Retention times are said to be of order of hundreds to thousands of years with greater than 99% probability. We envision placing the EHM motor in conjunction with the CO2 capture device as shown in Fig. 7. The EHM engine would be placed horizontally to avoid typical oil accumulation in one cylinder, as experienced by airplane engines. On the lower side of the motor the crankshaft connects to the transmission, while the upper side contains the turbogenerator. Two or three hydrogen storage tanks would be placed under the passenger seats. The front of the engine exposes first a large air filter and then the CO2 14
capture columns. The columns have access to the NaOH reservoir. The NaOH solution pump is not shown. It is expected that some of the electrical energy generated from the turbo will be used to generate hydrogen to feed back into the intake manifold.
Fig. 7. Illustration of basic EHM system.
The EHM system is applicable to engines in boats, light airplanes, heavy trucks, and stationary applications. We intend to continue to build a functional virtual prototype that is robust with respect to finite element analyses that include vibration, temperature and stress. The next step after the virtual prototype is the production of a physical prototype based on the tested virtual design.
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REFERENCES 1. Honish, B. et al. Atmospheric Carbon Dioxide Concentration Across the MidPleistocene Transition. Science 324, 1551 (2009). 2. Berner, R.A. et al. GEOCARB III: A REVISED MODEL OF ATMOSPHERIC CO2 OVER PHANEROZOIC TIME. American Journal of Science, 301, 182 (2001). 3. Tripati, A.K. et al Coupling of CO2 and Ice Sheet Stability Over Major Climate Transitions of the Last 20 Million Years. Science 326, 1394 (2009) 4. http://www.esrl.noaa.gov/gmd/ccgg/trends/ 5. Lackner, K.S. Capture of Carbon Dioxide from Air. European Journal of Physics 176, 93 (2009). 6. http://www.transportation.anl.gov/pdfs/HV/2.pdf 7. Verhelst, S. et al. Hydrogen Fueled Internal Combustion Engines. Progress in Energy and Combustion Science, 35, 490 (2009). 8. Baciocchi et al. Process design and energy requirements for the capture of carbon dioxide from air. Chemical Engineering and Processing 45, 1047 (2006). 9. Stolaroff, J.K. Carbon Dioxide Capture from Atmospheric Air using NaOH Spray. Environmental Science and Technology 42, 2728 (2008). 10. Zanfir, M.
et al. Carbon Dioxide Absorption in a falling film microstructured
microcreactor : experiments and modeling. Industrial and Engineering Chemistry Research 44, 1742 (2005). 11. Margaria, R. et al. An Efficient CO2 Absorber for experiments on metabolism. Journal of Applied Physiology 14, 1066 (1959).
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