Pochari Systems is designing the next generation of diesel propulsion by building on the proven diesel engine and applying innovative solutions to fully eliminate all emissions while simultaneously increasing engine performance and efficiency by a large margin.The diesel engine has accumulated a rather poor image due to their perceived toxic pollution, primarily particulate matter but also substantial quantities of nitrogen […]
Pochari Systems is designing the next generation of diesel propulsion by building on the proven diesel engine and applying innovative solutions to fully eliminate all emissions while simultaneously increasing engine performance and efficiency by a large margin.
The diesel engine has accumulated a rather poor image due to their perceived toxic pollution, primarily particulate matter but also substantial quantities of nitrogen oxides.
Diesel is a power cycle, not a fuel per se. The diesel engine can theoretically run on any flammable fuel, provided there is sufficient temperature for autoignition. There is no reason or believe the diesel engine is destined to be polluting if designers and engineers choose to embrace this simple solution.
It so happens hydrogen is an ideal fuel for a compression ignition engine provided these innovative solutions are employed to overcome some inherent technical challenges.
These innovative solution is what we term the closed-cycle, the closed-cycle can be thought of as a multi-faceted series of solutions to problems inherent to hydrogen combustion engines.
The closed-cycle solves four major limitations faced by both conventional hydrogen engines and also non-combustion hydrogen systems, mainly PEM fuel cells.
#1 How does it work?
A conventional internal combustion engine which does not consume atmospheric air, thus stores oxygen onboard (for mobile applications) and recycles a working fluid, a non-nitrogen inert gas. The exhaust of a hydrogen engine is nothing but water vapor, no carbon dioxide is produced, therefore there is no need for exhaust, as there is no pressure buildup from carbon dioxide gas being released with the combustion of hydrocarbons. Steam is the only bi-product. Steam is condensed in a specially designed condenser. Hydrogen engines inherently want to operate on a closed cycle, thus, any hydrogen engine designer not running on a closed-cycle is failing to realize a potential 50% increase in efficiency, and not fully exploiting hydrogen’s unique properties to eliminate all pollutants.
The basis of our technology is the conventional two or four stroke diesel engine.
Interestingly, the closed-cycle does not benefit at all from the 4-cycle the way conventional atmospheric engines do. As such, our engines will be designed as opposed-piston two stroke, similar to the Junker Jumos or the more recent Archates power.
Conventional atmospheric engines need to ingest as much air as possible during each intake stroke, then expel as much exhaust (primarily carbon dioxide gas) as possible during the exhaust stroke. Since there is insufficient time during the end of the power stroke and beginning of compression stroke for this to occur, efficiency is reduced, due to a shortage of oxygen and excessive concentrations of inert exhaust gas possessing a lower specific heat ratio.
In addition to an efficiency penalty, this two-cycle process results in more incomplete combustion, increasing particulate emissions.
This alone has forced the major manufacturer of two-stroke diesel engines to completely abandoned production in the mid-1990s.
Despite these disadvantage, the two-stroke possesses the major advantage of requiring 50% less weight and displacement to achieve the equivalent power output of its 4-stroke contemporary.
All the disadvantages of the two-cycle are only present with atmospheric engines.
With the closed-cycle, all of these problems are fully solved.
Theoretically, a closed-cycle engine does not even need an intake valve or an exhaust valve, as the oxygen and hydrogen can be both directly injected, and the water vapor can be purged with small ports.
When hydrocarbon is combusted, a very large amount of carbon dioxide gas is produced, requiring a high volume exhaust system, either large wall port valves in the case of a two-stroke, or adding two additional strokes to further complete the exhaust and intake process.
In order to increase the power output of a conventional atmospheric engine, a large increase in the quantity of oxygen is required in order to maintain stoichiometric combustion, this is typically provided by a turbocharger for diesel engines. This large intake massflow necessitates large overhead valves.
With a closed-cycle, only a method to remove and condense water vapor is required. A conventional wall port valve two-stroke (Detroit diesel architecture) but without overhead intake valves, is all that is required for efficient operation on a closed-cycle. A smaller exhaust and intake port is used to flush out a certain percentage of the water vapor produced each power stroke, freshly separated argon gas is circulated back into the same wall port valves, to replenish the argon in the chamber.
It’s desirable to maintain below a certain level of water vapor concentration in the chamber.
For most closed-cycle engines, oxygen will be injected in the intake manifold at at low pressure, as direct injection is unnecessary and adds additional cost and requires a new cylinder head to be fabricated to accommodate the second large injector. Any unburned hydrogen or oxygen is recirculated and combusted, achieving 100% combustion efficiency.
#2 What are the major major advantages?
#1 Near complete elimination of NOx
The first major advantage is the elimination of the only pollutant produced from hydrogen combustion: NOx. This finally makes hydrogen engines fully clean, as they currently are “quasi” zero-emission, producing no carbon dioxide or monoxide, as hydrogen contains no carbon, but still producing high quantities of nitrogen oxides, especially at stoichiometric air-fuel mixtures. The NOx emissions are especially exacerbated beyond acceptable levels if a diesel cycle is used. NOx emissions cannot be brought to acceptable levels without a very low equivelance ratio Otto cycle, but at the expense of power density.
For a diesel cycle running on a high hydrogen mixture, NOx emissions are as high as 920 ppm (R Kavtaradz 2019). This is way too high to be considered a low emission solution, therefor hydrogen diesel engines are doomed to failure unless these innovative solutions can be applied, this is why we consider the closed cycle to be essential.
A closed-cycle can be thought of as an extreme form of emission control technology, but with the added benefit of unexpected performance increases to be discussed below.
In conventional hydrocarbon engine design, there exists a strong conflict of interest between maximizing power and efficiency, but also attaining acceptable emission levels. With a closed-cycle, reducing emissions increases performance!
#2 Ability to use pure hydrogen in existing diesel engines, only technology in the world that can allow this.
The second major advantage is the ability to use pure hydrogen in a diesel cycle. Currently, hydrogen cannot be used in a diesel engine due to the very high auto-ignition temperature, which necessitates a 35:1 compression or 200 °C intake air temperature to achieve sufficient compression temperature for auto-ignition. Neither of these options is feasible. Pilot fuel can be used, but must be a hydrocarbon fuel since a high cetane number is required. The reason we want to use a diesel cycle is due to the great efficiency advantage over the Otto cycle, decreasing operating costs.
A hydrogen direct injection compression ignition engine with heated intake air (non-closed cycle nitrogen-oxygen) was demonstrated to achieve a tremendous 53% efficiency advantage over diesel fuel using a 10 hp test engine. The diesel engine was 27.9% efficient, vs 42.8% for the same engine with hydrogen injection. The power output of the hydrogen injection version was 15% higher. A hydrogen fuel injector was custom built in place of a swirl-chamber diesel injector. (JMG Antunes, R. Mikalsen, A.P. Roskilly, 2009).
Even better, Homan et al, 1979, found an astounding 60-100% efficiency increase using a large diesel engine (Caterpillar D399, V16, 1200 hp, 64 liter) with glow plugs for ignition assistance. The engine used port injection.
The huge increase in efficiency is mainly a function of the much higher cylinder pressure rise (ROPR) due to hydrogen’s higher flame speed. The cylinder pressure rise is in the order of 2.10x higher using hydrogen fuel over diesel fuel (Homan, Reynolds, De Boer, Mclean, IJHE 1979). Typical ROPR for a conventional direct injection diesel engine is in the order of 3 bar °CA at 2000 rpm (M Y.E. Selim 2000). Since this number is doubled, we can expect 6 bar °CA for a pure hydrogen direct injection diesel engine.
Thanks to the faster cylinder pressure rise, more work is accomplished in a much shorter period of time, this results in less heat lost by conduction through the cylinder wall, since there is less time for conduction to occur.
Heat loss through the cylinder wall into the coolant was estimated to be 42% of the total energy input for the diesel version, but only 17% for the hydrogen direct injection version. (JMG Antunes, R Mikalsen, A.P Roskilly 2009). The engine was 10 KW single cylinder indirect injection diesel engine (modified for direct injection H2). The rate of heat release (ROHR) for a 60% hydrogen content port injection diesel engine is 87 J°CA, vs 59 J°CA for diesel mode. The increase is much lower than would be the case for a pure hydrogen diesel engine (G. Mohan Kumar, 2017).
This data illustrates that hydrogen is a far superior combustion engine fuel, despite“experts”claiming only fuel cells can be used with hydrogen, and that combustion engines are not appropriate. No other fuel available can increase the efficiency of a diesel engine by 53-60% other than hydrogen.
#3 Across the board improvement in brake thermal efficiency due to higher heat ratio gas
The third major advantage is an across the board increase in efficiency of 25% regardless of whether a spark ignited or diesel engine is used. (P.C.T De Boer, J F. Hulet, 1980). The reason for the increase in efficiency is due to the specific higher heat of the non-nitrogen gas under the same compression, resulting in higher combustion temperature and greater power produced. With this increase in efficiency, a spark ignited engine can be 45% efficient, vs 35% for conventional Otto cycles. A diesel engine version could be 55%, making hydrogen engines equally efficient as fuel cells, yet available at a fraction of the cost.
#4 Ability to tolerate NH3 derived hydrogen with cracker average impurities of 500-1000 ppm.
The fourth major advantage and arguably the most important is the ability to use ammonia derived hydrogen.
Virtually all hydrogen used for ground-transport will utilize ammonia as a storage mechanism, allowing for the elimination of costly and heavy high-pressure tanks, and the elaborate and very costly infrastructure required for fueling.
Using onboard microreactors to convert ammonia back into pure hydrogen, to use in our closed-cycle engine, this allows a hydrogen vehicle to be fueled at home, and drastically reduces the cost of infrastructure conversion to build out a hydrogen mobility world. Ammonia is liquefied at 8-10 bar depending on temperature, and can be stored in plastic tanks.
The cracker uses 4.2% Wt Ruthenium and 10% Wt Cesium promoted CeO2 supported catalyst in a microchannel configuration.
The cracker specifications are based on Engelbrecht and Chiuta 2018, Chiuta and Everson 2015 and 2016, Di Carlo and Vecchione 2014 and Hill and Murciano 2014.
The activation energy is as low as 60-75 kJ/mol of NH3 with high cesium promoter loadings, which translates into only 5.5 KW/kg of H2 per hour, allowing for 90-100% of the required energy for decomposition is provided by exhaust heat from the diesel engine.
The amount of ruthenium and cesium needed is very minimal, only 0.001 kg and 0.005 kg respectively is required to reform 1 kg of hydrogen per hour at the desired efficiency and power density, translating into a material cost of only $160 for a 2 kg/hr cracker, sufficient for a medium-sized vehicle.
Cesium reserves are estimated to be 84,000 tons, with ruthenium reserves around 5000 tons, allowing for over 2 billion medium-sized car crackers to be produced.
Forming the tiny stainless steel microchannels from a solid block is performed by wire electrical discharge machining. Washcoating and packing of the catalyst inside these tiny grooves completes the manufacturing process of a microreactor.
Microreactor technology can be thought of as relatively simple compared to battery manufacturing as an example. The only complexities and difficulties arise from the very small dimensions
These small dimensions found in microreactors (as little as 0.15 mm x 0.25 mm) requires elaborate and costly machinery to fabricate, but nonetheless, the cost of the cracker will be approximately $1000-1500 per kg-hour of capacity at high production volumes, of which 15-20% represents material costs.
The ideal operating pressure is ideally as low as possible to achieve the highest conversion rate. A higher pressure reduces the conversion rate, but substantial reduces the amount of catalyst required, from 6x from a pressure of 1-10 bar. At 550 C, the conversion rate at 2 bar is 99.9, and reduced to 99.0 C. The ideal pressure was identified to be 10 bar as a balance between conversion rate and catalyst mass by P. N Ross 1982.
The ammonia cracker is located on the exhaust manifold for closed-cycle hydrogen diesel engines, utilizing engine exhaust heat supplying 100% of cracker energy needs, with a closed oxy-hydrogen combustion chamber to provide heat during startup. The volume of the ammonia cracker for a 20 kg/hr, enough for a large class-8 semi-truck at full power (550 hp), takes up only 20 liters, and weighs less than 10 kg!
The cracker is configured in a modular fashion. The modules consist of a housing, each consisting of multiple microchannel reactors inside, this housing is placed directly outside of the exhaust outlet in the cylinder head, with very hot exhaust gas passing directly into the microchannels, heating the catalyst bed to provide the necessary activation energy. Each module is connect to four rails, supplying both gaseous ammonia to the cracker, and passing reform gas to the purifier. The two smaller rails provide oxygen and hydrogen to provide heat during startup.
Cracker specifications based on Engelbrecht and Chiuta 2018, Chiuta and Everson 2015 and 2016, Di Carlo and Vecchione 2014 and Hill and Murciano 2014.
On-board vehicular micro-channel with Cesium promoted Ruthenium on Cerium Oxide catalyst.
Cracker located on exhaust manifold for closed-cycle hydrogen diesel engines utilizing engine exhaust heat supplying 100% of cracker energy needs, with start up heat supplied by high temperature oxy-hydrogen combustion.
type: Micro-channel stainless steel
Catalyst: 4% Wt Ru 10% Wt Cs promoted on CeO2
Ru Catalyst required per Kg hour H2 reformed: 0.001 kg
Ce Catalyst promoter per Kg hour H2 reformed: 0.005 kg
Gravimetric density: 0.50 kg/kg H2-hr
Volumetric density: 1 L/kg H2-hr
Energy consumption: 6 kw/kg H2-hr
Percent of reforming energy from exhaust heat: 100%
Conversion rate: 99.8%
Operating temperature: 500 °C
hydrogen consumed for dissociation: 0-10%, only during
Ammonia hydrogen density: 113 kg/m3
Ammonia consumption: 6 kg liquid NH3/kg H2-hr
Startup time: 10 minutes
Cracker cost: $1000-1300/kg-hr capacity
Ruthenium cost: $8000/kg
Cesium cost: $30,000/kg
A closed-cycle hydrogen compression engine is 55% efficient, resulting in around 35 kw of heat energy available for a 100 kw engine. As a result, 90-100% of the energy supplied to the ammonia reactor is free.
During lower throttle operation and startup, a small combustion chamber using hydrogen combusted with oxygen only, preventing NOx formation, can supply high temperature flame directly to the catalyst bed.
90-100% of the energy consumed by the cracking process is provided by the exhaust gas during higher speed engine operation, this is calculated by estimating the total heat energy provided by the exhaust gas adjusting for the greater exhaust loss portion rather than cylinder wall losses due to hydrogen’s higher LFS over diesel, resulting in a much greater percentage of losses through exhaust rather than coolant.
The oxy-hydrogen combustor chamber is closed-off from gaseous nitrogen produced from ammonia decomposition, preventing any NOx formation. The combustion chamber burn rate varies depending on the availability of exhaust energy, dependent on engine throttle. The oxy-combustion chamber provides very high combustion temperatures directly to the reactor, by burning the hydrogen in a pure oxygen environment.
The combustor is located in the module of which contains the reactor, which serves as the exhaust manifold, passing the hot exhaust gases through the heat exchanger tubes containing the reactor bed.
Our closed-cycle engine, due to utilizing a high-specific heat ratio inert gas, would have significantly hotter exhaust gas than with conventional engines, both since the compression temperature is much, as well the intake temperature, since the exhaust is routed back into the intake, but also since there is no CO2 to absorb heat, and since argon has half the specific heat capacity of air, the result is the exhaust temperature is likely to be 30% higher with a closed-cycle. The peak compression temperature of our engines will reach 950 C, 125% higher than with air.
The nitrogen bi-product is vented into the atmosphere after separation from the hydrogen, no oxidization occurs.
The nitrogen-hydrogen gas from the cracker, consisting of 75% hydrogen by volume, is passed through a membrane gas separation system to purify the hydrogen to 99.8% before being combusted in the engine, in order to minimize trace amounts of nitrogen oxidized during combustion, the resultant NOX is insignificant, being less than 6 parts per million, 19x less than Euro 6 vehicles.
The size and volume of the membrane separation system is minimal, taking up only 4.2 cubic feet and weighing 118 kg for a 7 kg/hr system, sized to power a 15,000 lb GW commercial vehicle.
The membrane separation system as shown above is comprised of an aluminum cylinder filled with a membrane comprised of tubes made of polyamide or cellulose acetate, or from ceramic materials. The membrane allows smaller molecules such as hydrogen to pass through and permeate perpendicular through the membrane tubes towards the outside of the cylinder, while the larger nitrogen molecules remain trapped inside and continue flowing parallel through the membrane tubes, the pressure is around 1 Mpa.
The differential in the permeation of nitrogen/oxygen is 3.43x for a rubber membrane, for hydrogen/nitrogen it is 5.92x, thereby increasing the effectiveness of the membrane separator by 74%, allowing for a reduction in size of the membrane separation system required over an oxygen/nitrogen separation, of which most separators are based on.
Membrane separator specifications based on Ube engineering
Membrane gas separator density: 49 L volume and 33 kg mass for a 27 Nm3/hr N2/O2 separator at 99% purity
Operating pressure: 1.4 Mpa max
Storing hydrogen as ammonia is a game changing solution, immediately rendering the entire current hydrogen mobility industry obsolete.
The high-pressure tanks, high-pressure fueling stations and PEM fuel cells manufacturers are faced with total obsolescence when closed-cycle ammonia fed hydrogen engines are available. The ammonia cracker can only realistically achieve a certain level of purity, small concentrations of ammonia will remain in the hydrogen, in excess of 500-1000 ppm being typical, increasing with lower reactor temperature. The maximum concentration of Ammonia tolerable by PEM fuel cells is in the order of 2.1 ppb (YA Gomez, 2018), that is parts per billion, and the ammonia concentration out of the cracker is 500-1000 parts per million, this is in the order of 240,000x more than the maximum purity requirement! this means there is an immense, possibly impossible filtration requirements in order to make PEM fuel cells compatible with ammonia derived hydrogen. If the concentration reaches 100 ppb, the membrane is damaged beyond repair (HMA Hunter, 2016). This 500-1000 ppm concentration of ammonia will cause almost immediate and serious damage and quickly result in the complete malfunction and destruction of the Nafion membrane critical to the operation of PEM fuel cells (FH Garzon, 2009, K Hongsirikarn, 2010). Thus PEM fuel cells cannot practically use hydrogen derived from onboard ammonia crackers without elaborate filtration systems to eliminate traces of undecomposed ammonia.
As a result, PEM fuel cells may eventually be made obsolete. Alkaline fuel cells can tolerate ammonia, but have poor longevity and durability, illustrated by complete abandonment of Alkaline fuel cells by the current hydrogen mobility industry.
Alkaline cells have a lifetime of 5000 hours only, compared to 10,000 or more for diesel engines. In addition to poor durability and higher cost, fuel cells, both Alkaline and PEM, do not provide the necessary waste heat to utilize for cracking the ammonia.
As a result, much more energy will be required for ammonia decomposition if a fuel cell is to be used instead, around 25% of fuel flow.
An internal combustion engine (especially a closed-cycle) is a perfect match for an ammonia derived hydrogen vehicle. When the consumption of additional hydrogen required for NH3 disassociation is accounted for, the net efficiency of a fuel cell at a starting efficiency of 55% is reduced to 44%, while the closed-cycle diesel engine remain at it’s starting efficiency of 55%.
#3 Why can our engine operate on a diesel cycle whereas other hydrogen engines such as Keyou and BeHydro cannot?
Thanks to the closed-cycle, we can use an inert gas (not nitrogen and air) which heats up to a much greater degree under the same compression (called the specific heat ratio) allowing us to attain a temperature sufficient to auto-ignite hydrogen, without requiring a high cetane number hydrocarbon pilot fuel, Dimethyl Ether, Biodiesel B100, or straight diesel fuel can be used, but not in a closed-cycle, as CO2 buildup will be unmanageable.
With Argon gas, with an intake temperature of 100 °C, a 17:1 compression ratio results in a temperature of 900 °C, 300 °C over the auto-ignition temperature (Checalc.com, using Peng-Robinson EOS). With a 22:1 CR, the compression temperatures reaches 1045 C, resulting in very short ignition delays. JMG Antunes et al found that under 830 C, the ignition delays is longer with hydrogen than for hydrocarbon fuels, but at or above 830 C, the ignition delay is much shorter. Argon, can be seen as an enabler to hydrogen compression ignition, (Mansor and Shioji 2012).
The higher intake temperature is a result of the closed cycle system, which routes the exhaust right back into the intake, instead of sucking in cooler ambient intake air as with an atmospheric engine. With an intake air temperature of 70 °C, a compression ratio of 35:1 is required to auto-ignite hydrogen with an oxygen-nitrogen mixture, making hydrogen compression hydrogen engines nearly impossible, limiting hydrogen engines to Otto cycles, which are limited to 35% efficiency.
#4 How is our engine different from existing internal combustion engines?
It is not different at all. The engine can either be spark ignited, or compression ignited, exactly the way current engines reciprocating engines operate. Although it is apparent spark ignition is obsolete with closed-cycle engines, as the only advantage spark ignition offers for conventional engines is a reduction in emissions and noise, but the first issue, arguably more important, is completely eliminated, thus spark-ignition is no longer attractive, therefor, it is likely nearly all closed-cycle engines will be compression ignited.
In compression-ignition versions, the fuel (hydrogen) is injected direct, oxygen is injected into the intake manifold. The inert gas is passed through the condenser, removing the water vapor, then recycled continuously until CO2 concentration reaches 15%, then the argon gas vented and replaced, this occurs every 30 minutes.
Theoretically, any type of engine or power cycle can operate on a closed-cycle, but some are more congruent than others. Two-stroke diesel engines are ideal, being nearly perfect.
#5 Since it’s a closed cycle and does not consume atmospheric air, we have to consume oxygen, does this increase the cost? Short answer: On the contrary, it significantly reduces operating costs thanks to higher efficiency.
Oxygen’s abundance and therefore low cost and high storage density in liquid form allows us to store the necessary quantities required while imposing little to no penalty on operating cost or vehicle weight or volume.
1kg of hydrogen requires 7.4 kg of oxygen for complete combustion, what we call the stoichiometric ratio. For atmospheric air, this ratio is 2.9% hydrogen to atmospheric air by mass. This small ratio is what makes the closed-cycle so attractive, very little oxygen is actually required compared to the engines’ mass airflow in conventional operation. This is because normally diesel engines run very lean, a low equivalence ratio, to minimum NOx formation.
Thus if our engines consumed 8 kg of hydrogen per hour or per 60 miles (based on 5.9 mpg for a typical semi-truck or 250 brake horsepower, corrected for the efficiency improvement) we only need 60 kg of oxygen. Storing enough oxygen to drive 850 km only requires 580 liters for liquid storage.
The weight of the oxygen storage is also minimal for mobility use. For a hypothetical 9000 lb light-duty truck (Ford F-450) with a 500 miles range, the oxygen tank weighs 240 lbs, plus 440 lbs for the oxygen, representing only 4.5% of the vehicle’s GVWR. Thus, storing liquid oxygen onboard a vehicle, may at first seem almost science-fiction-like, but in reality, is it least of the operators’ worries.
For stationary applications, oxygen can be stored in large spherical liquid tanks or can be piped directly in low-pressure gaseous form. For stationary storage, due to oxygen’s very high density, the“boil-off rate”is minimal, 1.5%/day for a 200L dewar.
The liquefaction of oxygen is easily accomplished with low cost commercially available equipment. Due to oxygen having an inversion temperature above ambient, it requires no pre-cooling required with hydrogen liquefaction.
Liquefyng oxygen for transportation and storage is not only cost effective, but technically simple, requiring only compressors and expanders, all of which are widely available on Alibaba.com.
The cost of oxygen, either liquid or gaseous is very low due to its abundance. Liquid oxygen costs only $0.05/kg in India (Metals and Minerals Trading Corporation of India, 2016) and $0.08-0.09/kg in the U.S. (Matheson Tri-Gas, 2017).
Resulting in hourly operating costs of $4 and $7.3 respectively for a 300 hp engine.
A hypothetical 1000 hp (750 kw) diesel generator with a BSFC of 0.33 lbs/bhp-hr (41% efficiency) would consume 47.6 gallons of diesel fuel per hour, with the efficiency improvements from the closed cycle, this would be reduced to 40 kg of H2 per hour, requiring 254 kg of oxygen, at a cost of $14.8 per hour, contrasted to $140/hr for $3.5/kg clean hydrogen from electrolysis. Netting an electricity cost of $0.020/kwh. In comparison, a spark-ignited non closed cycle engine with a BSFC of 0.4 lbs/bhp-hr (34% efficiency) would consume 66 kg of H2 per hour, costing $231/hr, netting an electricity price of $0.31/kwh. This clearly illustrates that for any application, mobility or stationary power generation, the closed-cycle is much more cost effective and would yield operators much greater profits. A fuel cell powerplant, averaging over $2000-5000/kw, is not even comparable, as the acquisition cost for a 750 kw unit would be astronomical, totaling over a million and half dollars.
#6 What are the necessary modifications required to convert an engine to closed-cycle?
That depends on whether a spark-ignited or diesel engine is used. For spark ignition, the first modification required is a compression ratio reduction to 5.5:1 for a typical 11:1 compression ratio gasoline or natural gas engine. Reducing the compression ratio simply involves raising the cylinder head a small distance, this can be done by installing a thicker metal cylinder head gasket. The increase in height is around 0.2”. The fuel system on the conventional spark-ignited engine is removed and replaced with low-pressure constant flow hydrogen injection in the intake manifold. No specialized injectors are needed, simply a constant flow of low-pressure hydrogen is fed into the intake manifold.
Regardless of whether diesel or spark-ignited, proper crankcase ventilation is required for any hydrogen engine to ensure no build-up of hydrogen in the crankcase occurs. This can be accomplished by inserting a small vent in the crankcase, equipped with a hydrogen sensor, to monitor the potential accumulation of concentration of unburned gas.
The second modifications after the fuel system is the exhaust system. The exhaust tubing, condenser, and dual argon-CO2 vent tanks are filled up with argon, which is continuously recycled. Two tanks are used in order to maintain a 15% CO2 to argon ratio, as a small amount of lube-oil is burned, releasing CO2, the dual tanks are continuously switches, when one tank reaches 15% CO2 concentration, it is emptied and refilled with pure argon. More on this can be found on question #9.
The water vapor condenser is installed just before the intake, so that the exhaust gases have had sufficient time to cool down to the 100 °C intake temperature, allowing a certain percentage of the water vapor to have condensed.
For vehicle use. The liquid oxygen is used to accelerate the condensing of the water vapor, for stationary applications, where space is not as constrained, a larger condenser is used, eliminating the need for cooling.
The third modification required is the installation of an oxygen regulator. The oxygen regulator is located on the oxygen intake hose, which can be a low-pressure flexible line, connected to a high-pressure storage vessel for vehicle use, or a low-pressure supply line for stationary applications. The oxygen regulator is calibrated to provide a 7.4:1 ratio of oxygen to hydrogen by mass at any given engine speed. The regulator can be electronic or mechanical.
The fourth modification is the installation of two hydrogen sensors. A hydrogen sensor is installed in the crankcase, to warn the operator if any gaseous hydrogen has accumulated in the crankcase due to a blockage in the venting system.
The second hydrogen sensor is installed in the exhaust line, to measure combustion efficiency. If a high concentration of unburned hydrogen is detected, the oxygen regulator could be malfunctioning and the engine could be running too rich, the oxygen regulator is recalibrated to increase oxygen flow, until the unburned hydrogen concentration is reduced to normal levels.
For a diesel cycle, the modifications required are somewhat more elaborate but isolated to the injection system. In a diesel engine, precise injection of the fuel is critical for smooth and reliable operation. Intake injection is possible, through what is called homogeneous charge compression ignition (HCCI).
Fuel is mixed with the intake air, in this case hydrogen, oxygen and argon, then compressed until auto-ignition. This cycle is highly efficient, one study shows up to 12% more efficient than direct injection. (JMG Antunes, R. Mikalsen, A.P Roskilly, 2008). The main issue with HCCI is timing difficulty which results in rough and sporadic operation. Currently, no HCCI engine is in operation.
Pochari Systems strongly believes direct injection is the best option.
To perform the closed-cycle conversion for diesel, the first step is to remove the fuel injection system, the unit injectors, injection pump, fuel lines and ECM.
Newly built low-pressure in-direct oxygen injectors are installed in the intake manifold, in the same fashion as port fuel injection. The main injector, consisting of the high-pressure hydrogen injector, is fitted into the main fuel injector cup.
A new ECM is designed for injection timing, and in some cases, a mechanical timing system can be used.
Modern diesel injection systems are designed primarily to minimize particulate emissions.
Multiple injection cycles per stroke are common, very high pressure is used to atomize the fuel as much as possible to ensure complete combustion, all of this requires precise electronic timing.
It’s fair to argue a large portion of the modern electronic diesel injection system is solely designed for emission requirements, not for performance or efficiency.
With a closed cycle hydrogen engines, all current efforts to minimize emissions, often at the expense of performance, can be completely eliminated, freeing the designer to focus solely on performance and efficiency. This should not be understated, as basically all constraints of the diesel engine result from emission limits, with the closed-cycle, we’re completely liberated to design the world’s most powerful and efficient engine, no compromises are made whatsoever.
The hydrogen injector consists of a simple high-pressure system, where feed gas from the N2/H2 separator is fed at 150 psi into the engine driven compressor to the auxiliary tank, then fed to the unit injectors at 330 bar, the injector serves as a valve only. Hydrogen is injected in small bursts, starting at TDC, until BDC, allowing for moderate ROPR.
Three types of hydrogen injectors are available based on actuation method.
#1 Piezoelectric crystal actuation
#2 Electromagnetic solenoid actuation
#3 Hydraulic, mechanical or electronic actuation.
The hydrogen injectors do not greatly differ from a conventional liquid fuel injectors. No fuel atomization is required, eliminating the need for extremely high operating pressures commonly found in modern diesel engines (330 bar vs 3000 bar for common-rail), this reduces the design requirements on the injector.
A few minor challenges arise with hydrogen injection.
The first potential issue is the lack of lubricity with a gaseous fuel, but this has not proven to be an issue as many natural gas injectors have been successfully implemented and have proven to be reliable. .
The second potential issue is hydrogen embrittlement. The hydrogen molecule has a tendency to embrittle commonly used ferrous and nonferrous engineering metals. Simple solutions to embrittlement involve using a non metallic coating in the injector chamber. This coating can consist of ceramic or epoxy.
Pochari Systems will use piezoelectric hydrogen injectors with 5000 psi gas inlet pressure.
Since the NH3 cracker outlet pressure is only 7 bar, an engine driven multi-cylinder compressor is used to pressurize the hydrogen into an auxiliary tank to 330 bar. This allows the engine to be freely throttled above the cracker flowrate. The ammonia cracker provides a continuous flow of hydrogen, it does not allow rapid increases in fuel flow, the cracker imposes a limitation on the freedom of the driver to rapidly accelerate. As a result, an intermediate auxiliary high pressure tank is used. The compressor unit consists of a four cylinder oil lubricated double acting hydraulically driven piston reciprocating compressor. The compressor is directly mounted to the main engine’s accessory drive. The compressor continuously feeds into a small auxiliary 330 bar composite tank, this tank is sized for 25% of the hourly fuel flow at fuel engine speed. The tank holds approximately 3.6% of the total fuel capacity.
The compressor weighs 15 kg for a 8.6 kg/hr unit, the volume is only 6 liters. The compressor consumes 1.6 kw of mechanical power per kg of hydrogen to 330 bar per hour.
#7 Why use this cycle over conventional spark-ignited hydrogen engines?
Previous experiments with spark-ignited hydrogen engines have not shown promising results for one single reason. Hydrogen is very attractive as a means to reduce emissions, but in the absence of a closed-cycle, high amounts of nitrogen oxides are formed due to hydrogen’s high combustion temperature. Nitrous Oxide, one of the seven oxides of nitrogen, is an extremely potent GHS.
Nitrogen oxidization is a function of combustion temperature and dwell time, essentially how long the combustion occurs. The formation of NOx increase dramatically above 2500 F, peak flame temperature in diesel combustion can reach 4000 F, resulting in very high NOx formation, up to 1000 PPM. Thus any attempt to design a dual-fuel hydrogen-diesel engine such as BeHydro will be a failure. In the case of hydrogen, dwell time is reduced due to much higher flame speed (7-8 higher laminar flame speed).
In the case of combustion temperature, hydrogen tends to burn hotter than liquid hydrocarbon fuels, which results in more NOx formation. As a result, hydrogen engines which run at a stoichiometric ratio, 2.9% hydrogen to air by mass, emit excessively high NOx emissions, defeating the purpose of using hydrogen in the first place. As a result, hydrogen engine designers typically run the engine at a 0.5 Equivalence ratio, or twice the amount of air than stoichiometric.
This leads to a drastic reduction in power output, around 50% less power is developed. An example of this is the MAN hydrogen engine developed for buses in 2006. The engine was a spark-ignited, 12:1 compression ratio, direct injection, but only produced 270 hp at 2200 rpm with 13 liters.
The port injection version of this engine only developed 200 hp! This is about half the power produced by modern diesel engines of similar displacement. As a result, a customer that requires a 500 hp engine, be it for a truck or generator, would need 26 liters, doubling the weight and volume of the engine and doubling the acquisition and maintenance cost.
The other obvious reason aside from the reduction in power density is the fact that currently, hydrogen cannot be used in diesel engines, limiting it to 35% efficiency, spark-ignited Otto cycle engines.
In summary, conventional spark-ignited lean-burn hydrogen engines are very unattractive compared to conventional hydrocarbon engines, and completely uncompetitive compared to state-of-the-art diesel engines, and become nearly obsolete when a closed-cycle is available.
#8 Why hasn’t it been done before?
Mainly because all the research and interested is focused on batteries, and if there is any interest in hydrogen, it’s almost invariably focused on fuel cells. As a result, the easiest and simplest solution was ignored. Apart from us, no one aside from Keyou Gmbh and more recently a newly formed company BeHydro is focusing on hydrogen engines, and no one in the world yet is working on closed-cycle direct injection compression ignition hydrogen engines.
We encourage engineers, designers and inventors to build this technology as soon as possible, so we have made it open source.
The main applications for the closed-cycle is for mobility, mainly cars, light-duty trucks, heavy-duty trucks, marine, rail propulsion and also for non-mobilty, mainly decentralized power generation.
#9 Is lube-oil combustion and subsequent CO2 buildup in the closed-cycle going to be an issue?
Not at all. Modern diesel engines consume between 0.2-0.8 grams of lube oil per Kwh. This means if we have a 100 kw engine or 134 hp, we consume 0.176 lbs of lube oil/hr, that equates to 0.025 gal/hr, which produces 23.62 lbs CO2 per gallon (EIA), equating to 0.6 lbs CO2/hr, resulting in a volume of 3.35 ft3 per hour (CO2 density at 30 PSI and 100 °C is 2.87 kg/m3. The CO2 argon mixture is allowed to build up to 15% CO2 concentration, then vented into the atmosphere and switched to a secondary tank of pure argon, once the secondary tank again reaches 15% CO2, the tank is switched back, and this cycle is repeated every 5 minutes, maintaining a 15% CO2 concentration maximum, with an average of much less.
The argon tanks are sized to provide this ratio, and switched every 5 minutes. Argon consumption per hour is 6.3 kg, at a cost of $0.11/kg for liquid argon (Metals and Minerals Trading Corporation of India, 2016) resulting in $0.70/hr cost). The argon density at 30 psi and 100 °C is 2.57 kg/m3.
Thus claims that the closed-cycle “cannot work” due to CO2 buildup from lube-oil consumption are incorrect. P.C.T De Boer, the first person to experiment with a closed-cycle hydrogen engine, used the same solution for dealing with CO2 buildup. A small 3.5 cubic foot (28 liter) liquid tank placed inside the middle of the main liquid oxygen tank providing virtually no boil-off, will store enough argon for 23 hours of operation for a class-8 600 hp vehicle.
Thus argon consumption, or CO2 build-up, is a non-issue.
#10 What are the advantages of NH3 storage over high-pressure hydrogen?
Virtually all attention paid to alternative low emission mobility today is focused on either fully electric vehicles, where all the energy stored in heavy and slowly rechargeable batteries. If one mentions hydrogen, we immediately think of ultra-high pressure composite hydrogen vessels to power proton exchange membrane fuel cells.
These two technologies both face major technical and economic limitations that hinder future large scale deployment.
The major limitation faced by hydrogen mobility is storage, both onboard the vehicle and during stationary storage for distribution.
The current industry almost exclusively uses carbon-fiber and aluminum lined composite cylinders. These cylinders are very heavy, weighing around 0.46 kg/liter of water capacity, and cost over $50/liter. The major limitation of these systems is primarily low market competitiveness, stemming from high manufacturing costs.
In order to store enough hydrogen at 350 bar for 1380 miles of range, we would need over $330,000 worth of cylinders.
The cost of these vessels is in the order of $50 per liter (Liaoning Alsafe Technology Co), whereas liquid oxygen dewars with a very low 1.5% boil-off rate cost only $6 per liter (Shijiazhuang Minerals Equipment Co).
This is mainly due to the fact that although liquid dewars must withstand moderately high pressures to ensure a minimum safety factor in the event of a high rate of evaporation, the pressure requirements are manageable with conventional engineering materials, mainly stainless steel utilizing vacuum flask insulation technology.
In contrast, composite cylinders must not only withstand immense pressure, in the order of 350 bar, the cylinders must also possess sufficient impact resistance, of which carbon fiber performs very poorly due to its brittle nature.
The safety and certifications requirements for oxygen cylinders are high, but much easier to comply with due to the absence of any flammability risks. In the event of an impact, liquid oxygen will simply vaporize in the event of an impact.
oxygen is not flammable, it does serve as an oxidizer, and will
increase combustion intensity if in direct contact with a flame or
source of combustion. In our vehicles, there is virtually no storage
of gaseous hydrogen on board, only a small amount is present at any
given time in the fuel lines coming out of the NH3 cracker, this
amount of hydrogen poses a very small explosive risk compared to the
entire hydrogen capacity stored onboard. Due to these reasons, the
cost of manufacturing high-pressure hydrogen tanks is very high,
resulting in a total cost of $330,000 for total tank capacity enough
for a class-8 semi-truck with 1400 miles of range, or roughly 180 kg.
The comparable cost of liquid oxygen vessels is only $7000-8000.
The cost of liquid NH3 tanks is minimal.
The NH3 tanks are 0.25″ thick aluminum or stainless steel, weighing only 0.10 kg/L. The tank is designed with a burst pressure of 350 psi, or a safety factor of 2x. The pressure of liquid NH3 is 8-10 bar depending on temperature. No insulation is needed, nor are extremely thick tank walls.
In addition to the high cost of high-pressure hydrogen storage systems is the inferior volumetric density compared to the NH3 system. The volumetric density of the NH3 system is twice that of 350 bar system, taking up more precious volume on the vehicle. This translates into a savings of 100 cubic feet using an NH3 system for a class-8 truck with 1380 miles of range. The volumetric density advantage is due to the use of NH3 as a hydrogen carrier, increasing volumetric density by a factor of 3.9x over 350 bar composite tanks, also translating into tremendous tank weight savings, as NH3 is stored under moderate pressure (8-10 bar) allowing for thin-wall aluminum or stainless steel tanks. NH3 tanks would way 0.10 kg/L, vs 0.5 kg/L for 350 bar.
limitations of the high-pressure system cannot be isolated to onboard
Another major limitation, and arguably the biggest issue so far is found in the transportation, distribution, and compression of gaseous hydrogen. Compressing gaseous hydrogen to 350 or even in some cases 700 bar, is an immensely capital intensive and costly process. The energy consumption is in the order of 3kw/kg to 5000 psi.
The cost of a 7,000 kg/year capacity 300 bar two-stage diaphragm compressor is in the order of $20,000 (Shanghai Davey Machinery Co Ltd).
Reciprocating piston air compressors last on average 10,000 hours before needing major overhaul. A diaphragm compressor uses the diaphragm to protect the metal components from toxic gases through the use of a flexible membrane design to resist damage by toxic gas.
This is especially important for compressing hydrogen, as hydrogen can cause serious embrittlement damage to carbon steels, stainless steel, especially martensitic, Inconel and Titanium.
Among the commonly used engineering metals, only aluminum alloys is resistant to hydrogen embrittlement, but aluminum is not suitable due to the high temperature from compressing a moderate heat ratio gas such as hydrogen. Without the diaphragm, the compressor piston and cylinder and cylinder walls of a traditional piston compressor would become badly embrittled and require frequently overhaul. Assuming 10,000 hours for a conventional compressor, we can optimistically assume a diaphragm compressor would last approximately 1.5x longer before overhaul.
We assume an overhaul cost of 100% of the purchase price due to the expensive nature of hydrogen diaphragm compressors due to the stringent engineering and manufacturing requirements inherent to systems dealing with flammable gas in closed proximity to urban areas.
Thus, our levelized cost of hydrogen to 5000 psi is $1.62/kg for the first 15,000 hours.
required capital expenditure for a 100 kg/hr fueling station would
total $2,400,000 for the compressors alone, not including the
elaborate fueling nozzles, of which accurate market prices are not
available. Hydrogen fueling nozzles are designed to withstand immense
pressure, as a result, leakage is a major issue, posing serious
safety hazards to personnel, as a result, the nozzle needs to be
perfectly hermetic, causing incredible engineering difficulties,
resulting in very high manufacturing cost and short lifecycles
especially due to heavy usage by untrained persons.
Hydrogen compressors are already produced in large volume for industrial applications, thus, accurate market prices are available on industrial e-commerce websites such as Alibaba.com, this allowes to reasonable accurately predict the cost of establishing a large scale hydrogen mobility economy.
The equivalent NH3 fueling system would as simple as a large tanker trailer, with flexible composite hoses connected to simple liquid fueling nozzles. The NH3 fueling station could be as cheap as $20,000 for 100kg/day, the price of a 10,000-gallon tanker trailer, including the hose and nozzle system.
With this information in mind, the total cost to install enough fueling stations to serve the entire U.S semi-truck fleet would total $10.5 billion, an equivalent and even further decentralized NH3 system could be built for a tiny fraction.
This number is reached assuming a U.S semi-truck fleet of 2 million operating 10 hours per day, consuming an average of 8 kg of hydrogen per hour traveling at 60 miles per hour. This does not account for the geographic distribution of the fueling stations, and includes only the cost of the compressors, the main component of the fuel station, as high-pressure hydrogen cannot be feasibly transported, this means there must be viable method to transport gaseous hydrogen from production facilities, which through the necessity of requiring low-cost electricity, are often located substantial distances from major urban centers where most consumption occurs.
Production through electrolysis requires electricity below $3 cents/kwh to be competitive with hydrocarbon distillates which average under $3/gal.
$3 cents/kwh can be provided by hydropower, geothermal or wind, but preferably nuclear, as nuclear has tremendous scalability potential and can bypass the requirements to transport the gas long distances, small modular reactors are ideal for localized production.
In the absence of localized production capacity sufficient to meet large urban demand, large scale distribution networks must be constructed. Tube trailers suffer from very high transportation costs due to minuscule capacity.
natural gas pipelines are the only viable option available, but
require elaborate retrofitting, as hydrogen permeates through most
surfaces designed for the much larger methane molecule. Hydrogen
permeation through conventional pipelines requires expensive
retrofitting, which could severely hinder the large scale conversion
of natural gas pipelines.
Pochari Systems completely bypasses these virtually insurmountable transportation difficulties of gaseous hydrogen since NH3 is quite dense (113 kg equivalent hydrogen density) which allows for cost-effective long-distance truck transport without the high-boil-off losses and high cost of cryogenic equipment of liquid transport.
To summarize, the major advantage of NH3 over 350 bar compressed storage is as follows
volumetric density by a factor of 2x
#2 An order of magnitude reduction in infrastructure cost to accommodate a large fleet of zero-emission hydrogen vehicles.
#3 Ability to easily refuel the vehicle at home with minimal equipment.
#4 Increased safety from completely eliminating onboard storage of gaseous hydrogen.
#5 Reduced acquisition cost by a factor of 4.4x over a 350 bar composite system
#11 Our engine is dual fuel, how is that important over hydrogen-only mobility systems?
Pochari Systems strongly believes a versatile, cost-competitive, retrofittable, and multi-fuel low emission powerplant is critical to attaining large scale market penetration. Current electric or hydrogen only systems become inoperable in rural regions where fueling infrastructure is scarce, in the case of hydrogen, virtually nonexistent. Thus, a multi-fuel powerplant, that still remains capable of full zero-emission operation, but can switch to using a widely available fuel, will be in great demand, only our technology can provide this, no other fully zero emission system can simultaneously switch to conventional operation.
The important of multi-fuel capability should not be underestimated, as it will take a large investment and a long period of time for a large scale hydrogen (In our case NH3) fueling infrastructure to be fully established.
During this time, having the versatility of being able to quickly switch to diesel fuel operation is critical to high-utilization and profitable operation, of which is demanded by commercial operators.
The vehicle may be eventually exported to less developed countries, if the vehicle can only operate on hydrogen, this lowers the vehicle’s market value in regions with undeveloped hydrogen infrastructure.
Pochari Systems’ hydrogen diesel engines can be switched to diesel fuel operation in less than 5 minutes. The closed-cycle system is opened to the atmosphere, the oxygen intake is closed, and the intake system is open for consuming atmospheric air, using a conventional turbocharger.
The hydrogen injectors are switched to diesel fuel spray mode, as the injectors are developed from the start with dual fuel nozzles, the middle nozzle is used for oxygen, and the outer nozzle for liquid fuel. A conventional diesel injection pump is activated, and diesel operation can begin. The entire process can take less than 5 minutes.
This unprecedented versatility and convenience should not be understated.
Proponents of low emission mobility often underestimated the sheer time it will take for low emission mobility to make significant inroads in the highly competitive commercial vehicle market.
Until the time arrives when a large number of vehicles are operating, thus a widely distributed network of fueling infrastructure is available, dual fuel capability is a necessity to maintain profitable operation, especially in large geographical regions such as the U.S and China and India, the largest markets for commercial vehicles. These countries, due to their sheer size, will prove more difficult in building out fueling infrastructure.
may operate very long distances at a time, more than a thousand
miles, this requires the ability to fuel up at existing fuel stations
A great benefit of the dual-fuel system is the ability to use hydrogen mode (closed-cycle) in urban areas where pollution from diesel particulate matter is of greater concern.
When the vehicle shifts operation to more rural more sparsely populated areas, diesel fuel operation can commence, as there less concerns with pollution.
scenario can be envision where long distance semi-trucks traveling
long distances between major cities, where a majority of their time
is spent in rural areas, but at the end of the trip, considerable
time is spent loitering in large urban areas, delivering the freight
to distribution centers or retailers. Once again, it’s imperative to
reduce urban pollution from diesel vehicle, this dual-fuel capability
will allow all vehicles coming into to urban area to essentially turn
into full zero emission vehicles with the switch of a button.
This dual-fuel capability will be one of the strongest selling points of the closed-cycle after NH3 fuel capability over a conventional hydrogen mobility system, comprised of PEM fuel cells and high-pressure tanks. The NH3 tanks an serve as diesel fuel tanks if needed.
The oxygen tank can be simply left on the vehicle and emptied when in diesel operation.
The oxygen tank can also be used to store diesel fuel.
© 2019 Pochari Systems
Closed cycle working principle
Direct hydrogen injection
A closed-cycle powerplant with 1000 mile range for a class-8 semi-truck.