Hydrogen Internal Combustion Engine drivers
Reduction of carbon dioxide emissions is driving the investigation of alternative fuels, with hydrogen being considered as a possible solution.
Hydrogen has both technical and logistical advantages and disadvantages compared to other technologies, and it is generally accepted that the best solution depends heavily on application, as well as power train considerations.
Combustion engines have always produced tailpipe emissions, and although hydrogen engines remove fuel derived carbon dioxide from the exhaust, other emissions remain and need to be managed. The technologies and calibration approaches long established for gasoline and diesel fuel emissions control are relevant and helpful, but require adaptation and calibration to meet the new challenges.
Although the removal of hydrocarbon fuels removes the majority of particles produced in the combustion chamber, other sources remain in a hydrogen engine. Specifically, the thinner combustion quench layer can lead to increased combustion of oil. When the oil burns the hydrocarbon components form soot, but a small residual fraction will be incombustible metal oxide particles, in increased quantities due to increased oil consumption.
These metal oxide particles are small in size, and they can overlap the area between 10 and 23nm, in the regions where the proposed Euro 7 and Euro 6 "cut-off" lies. This means that counting efficiency on homologation tests will be greatly affected by even small changes in particle size.
Filter performance testing
While an after-treatment filter can capture these soot particles and prevent them reaching the tailpipe, the solid oxide particles may also be captured, and can not be regenerated (unlike the soot particles).
They may sinter and permanently increase the back-pressure of the filter, requiring a re-evaluation of appropriate filter candidates (materials, technology) to ensure performance durability in the new application.
Selective Catalytic Reduction (SCR) is a well established technique for controlling tailpipe NOx (together with LNT and other technologies).
The increased combustion temperature under some operating conditions of the hydrogen engine means that effective NOx control is crucial to meet emissions standards.
Over dosing with AdBlue (ammonia solution) will lead to ammonia reaching the tailpipe, itself a regulated pollutant. Underdosing leads to NO & NO2 reaching the tailpipe.
As ever, successful operation of an SCR system relies on having enough reductant available (either through dosing or storage) to successfully treat the arriving engine emissions, without releasing stored ammonia to the tailpipe, which can occur during sudden and rapid temperature increases at the catalyst.
Real-time measurement of NOx concentrations (and even cycle-by-cycle, since NOx is highly transient) form a valuable input to a predictive model for emissions, and in turn allow dosing of AdBlue to be matched to the reductant require, minimising the reliance on storage and risk of ammonia slip.
N2O is another regulated tailpipe emission (both toxic and with substantial global warming potential) which may be formed in the SCR system. Careful transient after-treatment control is needed to prevent formation.
Measurement and testing solutions
Particle size, number and mass
The DMS500 measures the full particle size distribution, with outputs including size, number and mass data.
Understanding of particle size informs filter technology selection, and engine developers can use this size information to evaluate alternative strategies and technologies for effective emissions control.
These insights are in advance of those provided by simple particle number (N/km) metrics, which are also available from the DMS500.
NO and NO2
The CLD50 and N2O50 analysers offer transient measurements of NO & NO2 and N2O respectively.
Able to measure both pre- and post-after-treatment with milli-second response times, the data offers users a detailed understanding of both engine out NOx and after-treatment performance, offering a route to improved calibration and minimised emissions.
Filter Testing Systems
The DPG offers users an automated filter testing system, with high repeatability and capable of rapid testing.
With standardised measurements of backpressure and filtration efficiency built in, and capable of both loading and regenerating filters, the DPG allows users to effectively and efficiently characterise candidate filters for the new set of challenges posed by hydrogen engines.
An optional ash doping system allows rapid loading of oil ash onto filters, allowing rapid evaluation.
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