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Argonne Captures Images of Hydrogen Combustion in Working Engine

A view of hydrogen combustion through an endoscope. The red and yellow areas show the more intense temperatures.

Engineers at the US Department of Energy’s Argonne National Laboratory have captured the first images of hydrogen combustion in an internal combustion engine operating at real-world speeds and loads.

The hydrogen combustion imaging is part of a larger project to optimize the efficiency of hydrogen-burning internal combustion engines.

Several years ago, X-ray images of combustion inside a diesel engine made by researchers in Argonne’s Engines and Emissions Group revealed an unexpected shockwave as diesel fuel spurted out of the fuel injector. This earlier research is helping to improve fuel injectors and increase diesel efficiency.

Using imaging tools and other standard engine measurement devices on a Ford single-cylinder, direct-injection hydrogen engine, Argonne mechanical engineers Steve Ciatti, Henning Lohse-Busch and Thomas Wallner are optimizing engine operation and identifying the root causes of combustion anomalies, such as pre-ignition and knock. These problems are more pronounced at high speeds and high loads. Argonne researchers observe 50 performance measurements during each engine test.

Researchers use ultraviolet imaging to capture images of combusting hydrogen inside the running engine.

Hydrogen’s visible radiation signature is barely discernible, so we focused on the chemical reactions of hydrogen and oxygen, called OH chemiluminescence, in the engine.

—Steve Ciatti, principal investigator

Hydrogen has wide flammability limits, so the engine does not need a throttle, a device that chokes the air/fuel mixture to control the engine power and hampers efficiency (a standard car today is 25% efficient; a hydrogen car could be close to 45% efficient), nor do they require exhaust after-treatment when operating correctly.

Hydrogen’s high flame speed also offers a chance to increase the power output without increasing engine size. Using a direct injection of hydrogen, the power density is roughly 117% that of an equivalent gasoline engine—and hydrogen ICEs start easily in cold weather. However, unlike liquid fuels, hydrogen has low energy density per unit volume, resulting in somewhat limited range by comparison. The significant increase in efficiency will help to mitigate this characteristic.

Hydrogen easily combusts, so researchers are experimenting with a multiple injection approach. They are injecting hydrogen directly into the cylinder once or twice during each combustion cycle, depending upon operating conditions. The goal is to determine the optimum timing and amount of hydrogen injected each cycle. The wrong mixture of hydrogen causes engine operation and emission problems.

The researchers are also experimenting with prototype injectors. Making them is a materials science and engineering challenge because the operating atmosphere is unusually hot and under high pressure. Sealing and cooling the injector becomes a critical task. Researchers are also determining the most efficient and cleanest way to run the engine without knock or pre-ignition, another technical challenge.

The team will next move its work to a 2.3-liter four-cylinder Ford hydrogen engine, and then integrate that engine into a flexible hybrid vehicle for further testing.

This research is funded by the DOE Office of Energy Efficiency and Renewable Energy’s FreedomCAR and Vehicle Technologies Program. Argonne researchers are collaborating with Sandia National Laboratories, Ford, BMW and the European Hydrogen Internal Combustion Engine (HyICE) initiative.



allen zheng

They could also do combined fuel combustion research as well. These could be as common as gasoline-ethanol mixes, or as exotic and layered as biodiesel-fossil diesel- ethanol-butanol-hydrogen combinations.
____Onboard hydrogen generator using high temp electrlysis (from hot post catalytic converter exhaust) on a conventional ICE fueled by fossil/bio derived fuels may help provide more complete, efficient, and cleaner combustion. This is another ara they could develop.

Roger Pham

Direct injection of H2 is the best approach. No need for throttle plate, control engine power using fuel injection only, like in diesel. Fill up cylinder with unrestricted air to cool the combustion chamber as much as possible, and if needed, overfill it with air to cool it even more, then start to inject H2 at thousands of psi during the compression stroke. The high expansion will cool the compression stroke significantly, hence reducing the work of compression, and reduce the risk of detonation or pre-ignition. Then, more net power will be recuperated in the power stroke. With piezo injector, the rate of injection of H2 can be precisely controlled in order to prevent pre-ignition. Also, with good cooling of combustion chamber with excess air provide by a blower, pre-ignition can also be avoided. Ah, yes, I've predicted efficiency as high as 45% for H2 ICE. Glad someone agrees with me!

Rafael Seidl

Roger -

regular gasoline engines use throttles to adapt the amount of oxygen in the charge to the amount of fuel required to statisfy torque demand. The objective is a stoichiometric equivalence ratio of 1, such that there is virtually no free oxygen in the exhaust. This is an absolute must of the three-way catalyst is to work it magic.

Hydrogen will ignite quite well in lean-burn concepts. Better yet, in certain conditions, once you manage to ignite it at all, the flame propagates so quickly that local temperatures do not stay high enough for the Zeldovich mechanism to produce much NOx. The snag of course is that you have to produce, distribute and store H2 to begin with.

Even if stored in liqued form, H2 is not injected into the intake manifold nor the cylinder as a liquid - the thermal stresses on the components would be too great and the risk of inadequate mixture preparation would be too great. Instead, H2 gas is introduced at moderate pressures to retain precise control over the amount injected.

Even so, it is widely acknowledged that pure H2 would permit greater thermodynamic efficiency in an ICE than gasoline, mostly because the compression ratio can be higher (14-15 is optimal) and the combustion is extremely rapid (nearly isochoric). The downside is that well-to-wheels efficiency is still worse than for diesels, especially if liquid H2 is used. Highly compressed H2 yields only so-so vehicle range of around 200 miles. Both forms of H2 storage present serious safety issues, relative to mature hydroocarbon storage technology.

Allen -

Arvin Meritor is one company that has developed a plasma-based on-board fuel reformer. The idea is to partially combust a small fraction of the fuel into H2 and CO in a very rich misture. This gas is mixed with the fresh air and raises the knock limit of the gasoline. The exergy loss in the reformer is overcompensated with an increased compression ratio.

Barry R. Guthrie

"Even so, it is widely acknowledged that pure H2 would permit greater thermodynamic efficiency in an ICE than gasoline, mostly because the compression ratio can be higher (14-15 is optimal) and the combustion is extremely rapid (nearly isochoric)."

I have a question about increasing the compressoin ratio and thermal efficiency that I have not been able to find any good explanations for why the same intake charge will give you higher thermodynamic efficiency as you incease the compression ratio?

I was thinking that the molecular fuel electrons are compressed and then greatly expand during combustion, but this is a kinetic mechanical process not a thermodynamic process.

Could it be that the higher compression adds more enthapy to the fuel to reduce the energy needed for combustion process?

Could it also be that the higher compression minimizes the molecular heat transfer and irreversibility between the fuel molecules and reduces combustion process losses?

Yes, there is a mechanical compression ratio limit due to sealing friction of the chamber.

Rafael Seidl

Barry -

please consult basic thermodynamic textbooks for more details.

In a nutshell, higher compression ratio means higher peak temperatures means higher Carnot efficiency. What matters is the density of the charge (mostly air). Until it starts to combust near TDC, the fuel's only contribution is that it soaks up compression heat during evaporation. Gasoline direct injection takes advantage of this to raise the feasible compression ratio from 10.5 to 11.5.

Diesel engines feature compression ratios of up to 24, though 17-21 are more common. In automotive applications, the trend is downward as high compression ratios require very tight seals between pistons and cylinder liners, and very strong and heavy crankcases. The extra friction reduces the thermodynamic benefits, which anyhow come at the expense of elevated NOx emissions. Optimal values for the compressio ratios of automotive engines would be 14-15, but diesels need to start even in very cold weather. For spark ignition engines, the fuel imposes an upper limit due to engine knock (except when using CNG or H2 fuels).

Roger Pham

Furthermore, Barry, higher compression imply more expansion for the product of combustion, hence more work done for the hot gas. Consider an engine with 8:1 compression ratio running at 28" manifold pressure, and another engine using the same fuel at 16:1 compression ratio but at 14" manifold pressure. Each engine will have the same charge concentration at TDC, hence the same combustion temperature and peak pressure after combustion. However, at BDC at the end of the power stroke, the low compression engine will discharge exhaust gas that is only expanded 8 times, thus still has twice the pressure as the exhaust gas of the high compression engine, and at a lot higher temperature than the exhaust gas of the high compression engine. This means that a lot more work is extracted out of the combusted exhaust gas of the higher compression engine, even though the two engines has the same combustion temperature.

U r right, Rafael, regarding injecting of LH2, the thermal stress would be unbearable. Furthermore, energy can be recuperated from the LH2 by turning it into gaseous form at thousands of psi temp using waste heat from the engine, using a high pressure pump similar to those used for pumping feed water in steam engine. The thousand-psi hydrogen gas can then be directly injected into the cylinder using precise piezo injector, and the high pressure hydrogen gas will do more work on the piston as it expand, hence we have a sort of open-cycle Rankine engine on top of an Otto-cycle engine. Thus, the energy used to compress or to liquefy the H2 is partially recuperable.

H2 energy should be compared to other forms as solar to wheel, and not as well to wheel, since it would be wasteful to convert carbon-based fuel to hydrogen.

The short range of vehicle on H2 means that H2 should be used for local commute only, and that Hythane (hydrogen/methane mixture of mostly methane) instead, would be better for occasional long-distance driving since it can give 3 times the range for the same volume in the same hi-pressure tank.

The danger of H2 is well recognized, but it has not stopped a world-wide effort on H2 research into its use as energy currency for the far future. Apparently, the dangers of H2 can be controlled using current technology. Furthermore,we have an analogy in that even though gasoline is a much more flammable fuel and more dangerous than diesel fuel or ethanol, gasoline is still a predominant fuel in comparison to the two safer fuels.

Rafael Seidl

Roger -

"H2 energy should be compared to other forms as solar to wheel, and not as well to wheel, since it would be wasteful to convert carbon-based fuel to hydrogen."

The real drivers behind the whole "hydrogen economy" push are natural gas companies and the nuclear industry. The notion of solar power is dutiful mentioned to give these players a fig leaf and fool a gullible public into believing that H2 is the greenest of green motor fuels.

If you're going to drive on solar power, biofuels are a much cheaper, safer and more convenient route than H2, which remains stuck in R&D even though many billions of taxpayers' money have been spent on the technology in both Germany (1980s) and the US (now). The rate of progress bears more than a passing resemblence to fusion research.

Biofuels, by contrast, are all liquid at normal pressure and temperature and cause substantially less net CO2 emission than mineral fuels do. If the agricultural and chemical processes were themselves powered by either biofuels or renewable electricity, they would truly be carbon neutral (but unaffordable).

That said, biofuels can be produced domestically, creating local jobs. They also represent the most reliable and least expensive way to sharply reduce the CO2 impact of any shift from Arab oil to domestic coal.

Personally, I would prefer to see us going straight to renewables only but that would require massive investments and a clearer appreciation of the economic and environmental consequences. At least we are finally seeing significant private investment in this nascent industry, though in all fairness Big Ethanol is also securing taxpayer subsidies and protectionist tariffs for itself. In this respect, the new kids on the energy block are no different than Big Oil (tax breaks in the use of public lands) and Big Coal (synfuel gambit).

Roger Pham

Rafael,you've made an astute assessment and a practical point. Indeed, the "Freedom CAR" initiative by the Bush Adm was mostly of disingenious motive, especially in the cancellation of the PNGV program that was aiming at producing a 80mpg family car. A very efficient liquid-fuel car would have been far more realistic in the short term than the nebulous hydrogen fuel cell vehicle, but if the 80mpg car were produced, then Big Oil would not have reaped the huge record profit as of recently. The 1.8 billions USD given for hydrogen research were given mostly to natural gas and nuclear interests friendly to the Bush Adm.
However, the law of nature is such that for every intended action, there will be unintended results or consequences. The money spent on hydrogen research have resulted in promises of high-efficiency and affordable H2 production. H2 can be produced in one step from solar or wind energy right at the source, and consumed at the source, without requiring large, expensive production plant that will require extensive energy used in transportation, and labor used in material processing at a production plant.
Howver, hydrogen promises may never materialize, or may be years or decades away. So, given the current infrastructure geared toward liquid fuel, xTL processes involving inedible biomass would be of far more immediate practicality rather than waiting for hydrogen to arrive. That is, for the current generation of vehicles. Still, I can't help it but get excited every time progress is made in hydrogen research. Such a clean, clean fuel that requires no catalytic converter, so simple that it can be synthesized in everywhere for immediate consumption or short-term storage...etc. For long term storage or transportation via interstate pipelines, hydrogen can be converted to methane via the introduction of CO2 during the synthesis process. Methane storage is a mature process and requires less space and less extreme condition.

The next debatable issue is which would be cheaper and more efficient to produce from biomass: methane gas, or methanol, or BTL products? Methane is widely used for home heating and can be stored, and has been satisfactorily adapted for used as transportation fuel. A vehicle can be made to run on both methane and hydrogen at high efficiency. So, if more realistic progress is continued to be made in the hydrogen front, then it would be wise to start researching on producing the next generation of vehicles to run on both methane/hydrogen using the same gaseous-fuel-injector and the same high-pressure fuel tank, so that, by the time hydrogen start to come out in large quantity at practical price, then no time will have been wasted waiting for the next generation of vehicles capable of running on hydrogen. Many states with chronic air pollution problem can hardly wait to have hydrogen cars coming on board soon enough, so that's will be where the first batch of hydrogen vehicles will be heading to. Biomass may never be enough to satisfy our ever-increasing transportation energy demand in the future when petroleum will run out.
I can see that most of your points are being accurate and practical. It's just that my aspiration is for longer term and further into the future.

Rafael Seidl

Roger -

H2 from renewables is ok as an energy carrier to dampen out fluctuations in the availability of primary energy (sunlight, wind, waves) and demand patterns. Specially adapted gensets or fuel cells can then bridge the gap. In desert regions, the water vapor could be condensed and the water recycled.

The alternative is to store excess electricity from renewables as potential energy by pumping water up into existing, fully amortized hydroelectric dams against the gradient. Since these dams may be far away and water pumps are imperfect, this may be less efficient but the incremental infrastructure cost would be lower. Of course, at some point you max out on hydro dam capacity and have to resort to hydrogen storage.

All of this is very different from using hydrogen as a motor vehicle fuel. The simple but inconvenient truth is that gases (especially methane & hydrogen) suffer from low energy density by volume (as opposed to by mass). Ergo, you need to do some fairly crazy things (cryotanks or compression to 300-700 atmospheres) to get competitive vehicle range.

Liquid fuels are much preferred for mobile applications. Given the quantities required, leveraging photosynthesis is by far the most cost-effective route to produce renewable fuels. In that context, by all means do look beyond the present corn ethanol horizon to dedicated energy crops, optimized biomass logistics and tailored fuel properties.

Barry R. Guthrie

Hi Rafael and Roger,

I've been traveling and didn't have a chance to get back to you and thank you for your comments and insights with the compression ratio characteristics.

Thanks again,
God bless you,


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