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Small-displacement two-stroke H2 engine could address performance and emissions cost-effectively for recreational market; potential for Asian motor vehicle fleet

Comparison of brake thermal efficiency and specific fuel consumption at rated power (ICOMIA Mode 5), hydrogen vs. gasoline engines. Oh and Plante. Click to enlarge.

A team at the Université de Sherbrooke, Québec, Canada has developed a prototype small-displacement (<250 cc), two-stroke, inline two-cylinder direct-injected hydrogen engine that achieves high fuel efficiency and very low emissions. David Oh and Jean-Sébastien Plante sought to develop an engine that would be production viable in the mid-term (5—10 years) with realistic costs under the constraint of the most stringent emissions regulations.

Such an engine could provide a cost-effective solution for small recreational vehicle- and motorcycle applications. It, or a scaled-up version, could also provide a solution for the Asian motor vehicle fleet, in which two-stroke engine vehicles constitute a major share—and contribute significantly to air pollution. Oh presented a paper on the work, which was the result of two years of research activity, at the ASME 2012 Internal Combustion Engine Division Fall Technical Conference.

The two-stroke engine has been favored for small recreational vehicles because of its high power density, low cost and simple, lightweight design, Oh said.

However, it has been blighted by very high unburned hydrocarbon (HC) emissions that, as a result of ever more stringent regulations, have caused it to be almost entirely forced out of the market in favor of four-stroke replacements. This is due to raw, externally premixed fresh charge comprising air, fuel and lube oil being short-circuited into the exhaust during the scavenging process. The lost available energy also results in poor off-design point fuel efficiency. Both problems are addressed in part with gasoline direct injection, but are only decisively eliminated (apart from trace emissions from the lube oil) using hydrogen as the energy carrier.

...The motivations for targeting this segment are manifold. For one, the [California Air Resources Board] CARB-established limit of HC+NOx emissions in the 7.4 kW rated power class represents a 92% reduction in the current Tier 4 (4 Star) regulations from Tier 1, from 67 to 5 g/kWh. A presently voluntary 5 Star designation would further halve that limit to 2.5 g/kWh. This has forced almost all two-stroke gasoline marine outboards out of the market, while engines producing over regulated limits are still being manufactured and sold under a corporate fleet averaging system by trading credits from engines generating less pollutants than the mandate with those emitting more. Even with the move to four-stroke engines, additional complexity will be necessary—possibly exhaust after-treatment—in order to fully meet regulations. This will incur significant extra costs that are proportionally highest yet least tolerable in the lowest power rating segments. The second motivation is a purely pragmatic one, since a modest output powerplant will also have concomitantly modest needs for hydrogen storage to achieve a targeted autonomy.

—Oh and Plante

Oh’s hydrogen engine matched the rated power of the original gasoline engine, with an achieved best-point gross indicated thermal efficiency is 42.4%. The brake thermal efficiency at rated power is 32.3%.

ICOMIA cycle NOx emissions and hydrogen consumption, efficiency-optimized calibration. Oh and Plante. Click to enlarge.

Weighted over the entire 5-mode ICOMIA (International Council of Marine Industry Associations) duty cycle, the gross indicated thermal efficiency is 36.3%; brake thermal efficiency is 25.5%; and brake specific NOx is 2.46 g/kWh, the majority of which is in the Mode 5 (maximum rated power) operating point that accounts for only 6% of the duty-cycle time. The NOx emissions can be reduced by 18% to 2.01 g/kWh with a 3.3% fuel consumption penalty.

The base of the hydrogen engine is a series-production 2009 model year two-stroke carbureted gasoline marine outboard with 9.9 hp (7.4 kW) rating. Initially the team looked at indirect and semi-direct injection strategies. These were hampered by low power and abnormal combustion events such as knocking, pre-ignition and backfiring, which worsened with increasing engine load. As a result, Oh and Plante abandoned these approaches and focused on a cost-effective direct-injection system.

Because the design target included low system cost and production viability, exotic hydrogen storage and one- off fuel delivery solutions were precluded. The duo selected compressed gaseous hydrogen at 350 bar and adapted air-assisted injectors from Synerject (earlier post).

They developed a new cylinder head yielding an increased compression ratio to incorporate the hydrogen direct injection system as well as to maximize thermal efficiency. The chosen geometry is a hemispherical bowl-in-head that is offset away from the exhaust ports with approximately central vertical positioning of the injectors and closely located sparkplugs. Generous squish promotes charge turbulence near TDC for rapid mixing and short combustion duration. The geometric compression ratio is variable from 12 to 14.5:1 using metal head gaskets of varying thicknesses.

Everything else—pistons, porting and crankcase, bearings, exhaust, etc.—were carried over from the production engine.

Lubrication proved to be an issue. Initially, they used an off-the-shelf, synthetic-blend, TCW3-rated two-stroke engine oil. However, operation with hydrogen fuel resulted in severe black sludge on the piston crown and in the combustion chamber; hard varnish and rust on the cylinder liner and piston ring pack; and a foamy, white, mayonnaise-like substance indicative of aqueous emulsion and/or hydrogenation in the crankcase and ports. Switching to an unadditized Group III (severely hydro-processed) oil eliminated those issues.

In their study, Oh and Plante observed that late fuel injection is the key driver in raising the thermal efficiency, but at the expense of increased NOx emissions. They suggested that the cause of this is increasing charge stratification.

Since the low injection pressure limits the extent of realizable late timings and it is unlikely that the compression ratio can be further raised without increasing the tendency for abnormal combustion and NOx emissions, additional simultaneous efficiency improvement and NOx reduction will require substantial redesign with detailed determination of the sources of thermodynamic losses and novel approaches to their minimization. To this end, the effects of charge motion and stratification are to be investigated closer with direct in-cylinder optical observation, experimental measurements and CFD analysis. Wall-heat transfer is identified as the predominant loss factor based on a literature review, combining the small engine dimensions and very high compression ratio—with the consequent disadvantageous exposed surface-to- volume ratio—and the peculiarities of hydrogen combustion with its small quenching distance and high flame speed. Therefore, the systematic mitigation of wall heat transfer by imposing designed regimes of charge stratification and flow motion in the combustion chamber for reduced thermal convection is the subject of further work.

A gross indicated thermal efficiency of 45% and engine-out, cycle-weighted indicated specific NOx emissions of 1 g/kWh are targeted.

—Oh and Plante

Hydrogen two-strokes. Although Oh and Plante are targeting the recreational market with their development work, a low-cost, efficient and low-emitting small displacement two-stroke engine could have a significant impact in transportation markets in Asia.

In 2004, Asif Faiz and Surhid Gautam, both of the World Bank, published a paper in the International Journal of Vehicle Design exploring different technical and policy options for reducing emissions from 2-stroke engines.

In South Asia, these vehicles account for about 60% of the motor vehicle fleet and contribute significantly to air pollution, resulting in adverse health effects, particularly for urban dwellers. They are a major contributor to particulate matter (PM) and hydrocarbon emissions, besides visible smoke. PM emissions from a typical 2-stroke engine used in South Asia are an order of magnitude higher compared to a 4-stroke engine of equivalent size. Poor vehicle maintenance, misuse of lubricants, and adulteration of gasoline exacerbate emissions from these vehicles.

—Faiz and Gautam (2004)

In their paper, Faiz and Gautam suggested that emissions from existing 2-stroke gasoline engines could be reduced by using the correct type and quantity of lubricant, improving vehicle maintenance, and improving the quality of gasoline. For new vehicles, they suggested redesigning 2-stroke engines to decrease scavenging losses, and installing catalytic converters to reduce tailpipe emissions. Other technical options they identified included replacing the 2-stroke engine with a 4-stroke gasoline engine—or by switching to cleaner alternative fuels such as liquefied petroleum gas, compressed natural gas, or electricity.


  • David Oh and Jean-Sébastien Plante (2012) A Hydrogen-Fueled, Direct-Injected, Two-Stroke, Small- Displacement Engine For Recreational Marine Applications With High Efficiency And Low Emissions. (ASME ICEF2012-92047)

  • Faiz, Asif; Gautam, Surhid (2004) Technical and policy options for reducing emissions from 2-stroke engine. International Journal of Vehicle Design, Volume 34, Number 1 doi: 10.1504/IJVD.2004.003891



Plus, it sounds like it would make an excellent range-assist engine for electric vehicles!


O"K they now have hydrogen engines and fuelcells. What about the hydrogen infrastructure. There is numerous methods to produce hydrogen at low cost. When will someone open a hydrogen station with relevant high technology with hydrogen been made by machines on-site.

Roger Pham

H2 infrastructure is the easy part. To provide access to a H2 station within 5-7-mile driving distance, we will only need one station for every 100 square mile area in urban area, the H2 station will be located within the center of that 100-square-mile area.
Assuming a relatively low urban population density of 10,000 per sq.mile, then one single H2 station can serve 1 Million persons. Densely populated cities in the world may have population density of 50,000/sq.mile!

Assuming that only 1 person in 1000 will need access to that H2 station, this means that that single station can have as many as 1000 customers. Assuming that H2-Vehicles will need on average one fill up every 7-10 days, then each station will serve on average over 100 customers per day. Assuming 120 fill-ups per day and $25 per fill-up, then daily revenue will be $3000 and yearly revenue will be $1.1 million USD. Enough business to pay for itself within just a few short years. Since this is a money-making proposition, to assure enough H2 station to be present at mass roll-out of H2-FCV in 2015, the car dealers can join with the automakers to finance the opening of these H2 stations.

Since one station can serve a population of 1 million persons initially, the USA will need only a minimum of 300 stations. If rural areas along highways corridors will be included, the number of stations may have to be increased to 500. Assuming $1 Million cost per station, then the total cost of building enough H2 stations by 2015 will be only $300-500 Million USD. This is pocket change for the auto industry with gross revenues in the tens to 100 billions USD yearly.


One station per million people would leave the entire states of Montana and North Dakota with no place to fuel.  The geographic constraints of full coverage require a much higher station count.

Of course, those states also have little or need of H2 engines to mitigate air pollution.


I won't drive 5-7 miles to fuel my car any time soon. And if a million people are refueling at the same station, it may get a little crowded, no matter how many mpg we get.

Roger Pham

Of course, smaller H2-stations will cost less, perhaps 1/2 million USD a piece, and the number of stations can be doubled for the same cost, and can be put in areas of lower population density. In Interstate HWY's, a station will be needed every 33 miles or so, so about 30 stations per 1,000 mile long Interstate. If driving distance is kept to 7-10 miles to H2-station, then 1 station can cover 200 square miles, for population density at 5,000 persons per sq. mile.

If it gets crowded at the station, then the market force will dictate more number of stations in a given area when the number of FCEV's will pick up with time.


I saw a piece on the beeb website a few years back about a university team that was developing a trike with computer-controlled suspension and a rear-mounted H2 (I believe) ICE. This sounds perfect for such an app. I'll bet it would really fly.


Didn't BMW modify one of their car to use hydrogen instead of gas-diesel?

To equip USA's highways with hydrogen filling stations every 200 miles or so, (initially for FC trucks and buses) is not a real challenge. Something like 500 stations would fill most of the needs if installed at North-South and East-West hi-way crossroads.

Of course, many of those stations could also be used by urban buses, local FC vehicles etc.


Yes, BMW had a dual H2/gasoline V12 car.  It made less than 200 HP on hydrogen.

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