Why would part-load operation show a larger effect than full load?

At the established-physics tier the argument is about how much room is left. A modern electronically managed diesel at or near rated load is already running close to its designed optimum for injection timing, boost and air-fuel ratio, so there is comparatively little combustion incompleteness available to improve. At light load, at idle, and on older or less tightly managed engines, combustion is generally less complete, so an improvement in flame speed and burn completeness has more to act on. That is the reasoning; it is not a claim of a specific figure for your equipment.

Does that mean it will not help a highway truck at steady full load?

It means you should be more sceptical of claims made for that case, not less. Steady, high-load, modern, well-maintained highway operation is the duty cycle in which the published literature gives the least reason to expect a large change, and we say so. We do not tell operators of those fleets that a big result is likely. Anyone who does should be asked for their controlled baseline data.

What sort of equipment is this page actually about?

Refrigerated trailer units running independent of the main propulsion engine, often at steady part-load for long hours; camp, site and standby generator sets frequently loaded well below their rated capacity; and any machine with a duty cycle dominated by idling, light load or long low-load periods rather than sustained rated output.

Is running a genset lightly loaded a problem in itself?

Extended light loading is a well-known operational topic for diesel gensets and is addressed by generator manufacturers and service literature in their own right. We are not offering a remedy for it, and fitting a combustion-enhancement system is not a substitute for correct sizing, loading practice or maintenance. Our point is narrower: it is the duty cycle in which the published work reports the most room for combustion-completeness improvement.

How do I find out whether it does anything on my duty cycle?

Measure it. Record a baseline over enough hours or kilometres on your own equipment and duty cycle, with the same fuel and the same operators, then repeat it. Litres per hour for gensets and reefer units, litres per 100 km for road vehicles. The method is set out on the fuel efficiency page. We publish no headline performance percentage of our own precisely because your duty cycle, not our marketing, determines your result.

Usage case · duty cycle

The literature's own caveat, promoted to the headline.

Elsewhere on this site, "results are strongest at part-load and on older, less-optimised engines" appears as a caveat under the evidence. On this page it is the subject. If your equipment idles, runs lightly loaded, or is an older unit, the published work gives more reason to investigate. If it runs steady and near rated load on a modern engine, the same work gives you reason to expect less — and we would rather say that than sell past it.

Short answer

Which duty cycles does the published evidence favour?

Part-load, high-idle and older or less tightly managed engines. Independent studies of hydrogen and oxyhydrogen enrichment report effects that vary strongly with operating point rather than applying uniformly, and the reported fuel-consumption reductions across this literature sit broadly in the single-digit to mid-teens percentage range, with several studies reporting little or no benefit. Steady full-load operation on a modern electronically managed diesel is the case with the least headroom, and we do not encourage optimism about it. We publish no headline performance percentage of our own.

Reefer units: independent refrigeration engines, long hours, often steady part-load.
Camp, site and standby gensets: frequently loaded well below rated capacity.
High-idle and light-load plant: loaders, service trucks, support equipment.
Least favourable case: modern engines held near rated load — expect less, not more.

1 · What the studies report, per study

Load-dependence is the finding. Not a single number.

Each entry below is what that paper reported on its own test hardware, at its own gas fraction and operating points, with the conditions and the limits stated. Nothing is blended into an average, because the load-dependence is exactly what an average would destroy.

Saravanan & Nagarajan (2008), Int. J. Hydrogen Energy 33(6)

Reported: Reported improvements in brake thermal efficiency and reductions in incomplete-combustion products with hydrogen-enriched intake air, with the response varying markedly across the load range rather than being uniform.

Test conditions: Single-cylinder direct-injection diesel engine, hydrogen enrichment of intake air at fixed flow, steady-state dynamometer loading swept across part and higher load points.

Limits of the result: A research engine under controlled bench conditions. The load-dependence is the transferable observation, not the individual figures.

https://doi.org/10.1016/j.ijhydene.2007.12.065

Karagöz et al. (2016), Int. J. Hydrogen Energy 41(1)

Reported: Effects scaled with hydrogen energy share and with operating point; the paper's largest emissions changes appear at specific conditions rather than uniformly across the map, alongside an increase in NOx.

Test conditions: Single-cylinder diesel research engine, bottled hydrogen at several energy-share levels, constant speed, dynamometer loading.

Limits of the result: Hydrogen energy fractions used in some research conditions are higher than an on-demand system produces; treat the direction, not the magnitude, as informative.

https://doi.org/10.1016/j.ijhydene.2015.09.064

Yılmaz, Uludamar & Aydın (2010), Int. J. Hydrogen Energy 35(20)

Reported: Reductions in carbon monoxide, unburnt hydrocarbons and smoke opacity with a small hydroxy (HHO) fraction, with the size of the change differing by engine speed.

Test conditions: Compression-ignition test engines on diesel fuel with an on-board HHO generator, bench testing at varied speed.

Limits of the result: Speed-dependence in the results is one reason a single headline percentage cannot be lifted from this work.

https://doi.org/10.1016/j.ijhydene.2010.07.040

Uludamar et al. (2016), Int. J. Hydrogen Energy 41(26)

Reported: Emissions changes with hydrogen and oxyhydrogen addition on an unmodified engine varied with both engine speed and base fuel, several test points landing in the single-digit to low-double-digit range.

Test conditions: Unmodified multi-cylinder compression-ignition engine, low-sulphur diesel and biodiesel blends, gas inducted at fixed flow.

Limits of the result: Useful precisely because the engine was unmodified and production-representative; still a bench test at set speeds, not a duty cycle.

https://doi.org/10.1016/j.ijhydene.2016.03.179

These are independent laboratory results, not statements about our products. Smoke-opacity findings from the same pool, with the NOx trade-off disclosed, are on visible smoke reduction; the wider reading, including the negative results, is on evidence review.

2 · Mechanism, at the established-physics tier

Headroom is the whole argument.

A modern diesel near rated load is operating where its manufacturer's calibration was optimised: injection timing, boost and air-fuel ratio are close to their designed best, and combustion is already relatively complete. There is not much incompleteness left for anything to improve.

At light load, at idle, and on older or less tightly managed engines, combustion is generally less complete. Hydrogen's higher flame speed and wider flammability range act on the completeness and phasing of the burn of the primary diesel, so there is simply more for that effect to work on. That is the extent of the mechanism claimed anywhere on this site — the gas path is described on how it works.

Nothing here is a claim about your engine specifically, and none of it implies a compliance, certification or emissions-test outcome.

3 · The duty cycles this describes

Reefers, camp gensets, and anything that idles for a living.

Refrigerated trailer units

A reefer's refrigeration engine runs independently of the prime mover, for long continuous hours, typically at a steady part-load set by box temperature and ambient rather than by road speed. It is close to the operating pattern the literature is most interested in — and its fuel is often a separate, poorly instrumented line item.

Camp, site and standby gensets

Site power is very often loaded well below rated capacity, especially overnight and out of season. Consumption is measured in litres per hour on a machine that runs for thousands of hours a year, which also makes it one of the easier duty cycles to baseline honestly.

High-idle and light-load plant

Service trucks, loaders and support equipment that spend a large share of engine hours idling or lightly loaded between tasks. Engine hours accumulate whether or not work is being done, which is what makes the light-load portion of the cycle worth examining at all.

Related reading: generator sets, mining, agriculture and marine. Where fuel is carted to site, the dollars behind any percentage change too — remote fuel logistics cost. On biodiesel and blended fuels, see hydrogen with biodiesel blends.

4 · Read this as a limit, not a licence

This page should make you harder to sell to.

We do not claim a benefit for every duty cycle. The honest reading of this literature narrows the cases where a meaningful result is plausible; it does not widen them.

If a supplier tells you to expect a large, reliable saving on a modern fleet running steady highway load, that claim is not supported by the work cited here. Ask for the controlled baseline.

No compliance, certification or emissions-test-passing outcome is claimed or implied, on any duty cycle. Measurement method is on fuel efficiency; first-party operator data is on field results.

Model my own duty cycle Compare systems

No projected, typical or expected fuel-saving figure is published. Actual results vary materially with engine condition, duty cycle, load profile, fuel quality, installation and operating conditions. A controlled field evaluation on your own equipment, with baseline data captured before installation, is required before any commercial projection.

FAQ

Idle and part-load operation: common questions.

Why would part-load operation show a larger effect than full load?: At the established-physics tier the argument is about how much room is left. A modern electronically managed diesel at or near rated load is already running close to its designed optimum for injection timing, boost and air-fuel ratio, so there is comparatively little combustion incompleteness available to improve. At light load, at idle, and on older or less tightly managed engines, combustion is generally less complete, so an improvement in flame speed and burn completeness has more to act on. That is the reasoning; it is not a claim of a specific figure for your equipment.
Does that mean it will not help a highway truck at steady full load?: It means you should be more sceptical of claims made for that case, not less. Steady, high-load, modern, well-maintained highway operation is the duty cycle in which the published literature gives the least reason to expect a large change, and we say so. We do not tell operators of those fleets that a big result is likely. Anyone who does should be asked for their controlled baseline data.
What sort of equipment is this page actually about?: Refrigerated trailer units running independent of the main propulsion engine, often at steady part-load for long hours; camp, site and standby generator sets frequently loaded well below their rated capacity; and any machine with a duty cycle dominated by idling, light load or long low-load periods rather than sustained rated output.
Is running a genset lightly loaded a problem in itself?: Extended light loading is a well-known operational topic for diesel gensets and is addressed by generator manufacturers and service literature in their own right. We are not offering a remedy for it, and fitting a combustion-enhancement system is not a substitute for correct sizing, loading practice or maintenance. Our point is narrower: it is the duty cycle in which the published work reports the most room for combustion-completeness improvement.
How do I find out whether it does anything on my duty cycle?: Measure it. Record a baseline over enough hours or kilometres on your own equipment and duty cycle, with the same fuel and the same operators, then repeat it. Litres per hour for gensets and reefer units, litres per 100 km for road vehicles. The method is set out on the fuel efficiency page. We publish no headline performance percentage of our own precisely because your duty cycle, not our marketing, determines your result.

Where this applies

The verticals this duty profile describes.

Stop-start collection rounds, yard switching, route buses, camp gensets and pump sets — the applications where idle and part-load dominate the hour meter.

The literature's own caveat, promoted to the headline.

Which duty cycles does the published evidence favour?

Load-dependence is the finding. Not a single number.

Saravanan & Nagarajan (2008), Int. J. Hydrogen Energy 33(6)

Karagöz et al. (2016), Int. J. Hydrogen Energy 41(1)

Yılmaz, Uludamar & Aydın (2010), Int. J. Hydrogen Energy 35(20)

Uludamar et al. (2016), Int. J. Hydrogen Energy 41(26)

Headroom is the whole argument.

Reefers, camp gensets, and anything that idles for a living.

Refrigerated trailer units

Camp, site and standby gensets

High-idle and light-load plant

This page should make you harder to sell to.

Idle and part-load operation: common questions.

Why would part-load operation show a larger effect than full load?

Does that mean it will not help a highway truck at steady full load?

What sort of equipment is this page actually about?

Is running a genset lightly loaded a problem in itself?

How do I find out whether it does anything on my duty cycle?

The verticals this duty profile describes.

Commercial fishing →

Rail & locomotive →

Public transport & bus →

Waste & refuse collection →

Generator sets →

Generator-set classes →

Continue reading.

Hydrogen combustion enhancement

Engine performance improvement

Fuel efficiency

Emissions reduction

Visible smoke reduction

Remote-site fuel logistics cost

Generator-set classes

Hydrogen with biodiesel blends

Installation guide

Safety & compliance

Troubleshooting

Case studies & field results

Compare PEM systems

Does it actually work? Evidence review

How it works

PEM vs alkaline

Sizing combined gas

Four hydrogen technologies

Compared with Hydrogen Fuel Systems

Compared with H2i Technology

Compared with dynaCERT HydraGEN

Compared with HYDI

AU installation, warranty & safety

Mining fleets

Marine

Agriculture

FAQ