Learnings

Outcomes

A literature review was carried out in Phase 1 of this project. The review concluded that the behaviour of hydrogen methane blends in an internal combustion is complex, with multiple conflicting factors influencing efficiency and emissions, and that there is a lack of work investigating the behaviour of a Euro VI HD engine over a representative drive cycle. 

In Phases 2 and 3, a single cylinder thermal engine representative of a 13L Euro VI heavy duty engine was converted to run on methane hydrogen blends and commissioned. Testing was carried out at operating points representative of heavy duty truck operation with methane hydrogen blends up to 28% hydrogen by volume. Key conclusions and recommendations were:

Stoichiometric combustion

Analysis of test data indicated that for stoichiometric operation typical of current gas trucks: 

·        Brake thermal efficiency (BTE) with increasing hydrogen fraction was within 2% of the methane baseline for lower speeds and loads. At higher speeds and load a small degradation of 2% was recorded for more advanced ignition timings

·        Hydrocarbon emissions (HC) were reduced by the addition of hydrogen for all test conditions, reductions of 10-30% were observed

·        The effect of increasing hydrogen fraction on NOx emissions varied depending on test condition: at lower speed and load conditions, NOx was improved by 8-25% with largest improvements at 20% hydrogen fraction; at higher speed and load conditions increases of 8% were recorded. 

·        Engine out CO2 emissions varied with test condition depending on the carbon content of the fuel and BTE: at lower speeds and loads, emissions were reduced by 10%; whereas at higher speeds and loads CO2 emissions were increased by 5% with hydrogen methane blends. Well to wheel emissions will depend on hydrogen production method and biomethane content.

Chemkin modelling of stoichiometric hydrogen methane combustion showed good agreement with test data, and showed that the performance of a heavy duty engine fuelled by natural gas hydrogen blends would be expected to be similar to methane hydrogen performance measured during this project.  

Lean Combustion

For lean combustion, the addition of hydrogen extends the lean limit for stable operation from an air fuel ratio (AFR) of 1.35 to 1.55, with leaner operation enabling reductions in NOx. Hydrocarbon emissions were also reduced at leaner AFR for hydrogen methane blends. 

Drive cycle analysis

Analysis of test data over a typical heavy duty drive cycle with 20% hydrogen fraction showed improvements in HC and NOx emissions of around 15%, indicating a low risk of increasing emissions due to operation on hydrogen methane blends. CO2 emissions were reduced by ~5%. Gravimetric fuel consumption showed a slight reduction ~5%, however the lower volumetric lower heating value (LHV) of methane hydrogen blends at this hydrogen fraction would be expected to lead to higher volumetric fuel consumption with a commensurate reduction in vehicle range. 

Test results showed an improvement in NOx, HC and brake thermal efficiency (BTE) at lower load conditions, with degradation of NOx and BTE at higher speed and load conditions. Therefore, duty cycles with lower engine speed and load conditions, such as a bus cycle, would be expected to give greater benefits than the truck cycle studied in this work. 

Barriers to use of hydrogen methane blends in heavy duty trucks

Barriers to the use of hydrogen methane blends are summarised in the table below:

System
Description
Risk
Project outcome
Severity
Emissions performance
NOx emissions
NOx emissions are adversely affected by hydrogen addition
Project results show that, over the drive cycle analysed, NOx and CO2 emissions were reduced by 15% and 5% respectively for a 20% hydrogen blend
L
Engine control system
Air fuel ratio control
Stoichiometric conditions not met, engine operation away from design point, aftertreatment efficiency reduced
Air fuel ratio is commonly controlled via an oxygen sensor which is expected to operate correctly with hydrogen methane blends 
L
Ignition timing
Hydrogen addition reduces ignition delay, so combustion timing is not optimal impacting engine performance
Project results show engine performance is not very sensitive to ignition timing. Control systems are under development by OEMs to optimise spark timing
L
Aftertreatment
Conversion efficiency
Hydrogen addition reduces 3 way catalyst efficiency causing degradation in emissions
Literature shows 3 way catalyst performance is improved with hydrogen addition
L
Durability
Hydrogen addition impacts 3 way catalyst durability
Work is needed to investigate this effect
M
Gas quality
Wobbe index of gas blend
Variability of underlying natural gas composition means that addition of hydrogen reduces Wobbe index below the acceptable lower limit
This risk is present but can be mitigated through gas quality measurement at the hydrogen injection point, and potentially limiting the quantity of hydrogen added. 20% hydrogen addition is likely to produce a gas mixture that is acceptable to use in the majority of gas engines, but specific guarantees from OEMs may be required to ensure that performance and durability are maintained.
M
Vehicle range
Hydrogen blend energy content
Hydrogen blending reduces volumetric energy content of fuel, reducing vehicle range by an estimated 20% at 20% hydrogen blend
Likely to impact acceptability to operators, vehicle level tests needed to confirm effect
H
On board fuelling system
Compatibility with hydrogen blends 
Hydrogen addition causes failure of fuel tank or fuelling system, injectors, seals etc. Steel fuel tanks are particularly high risk
OEMs test components up to 2% hydrogen as this is the highest concentration permitted by the CNG as motor fuel standard (DIN 51624). 
H
Vehicle standards
Hydrogen fuel content limit
Current vehicles are homologated to up to 2% hydrogen fuel content (note that higher levels of hydrogen are permitted for industrial engines that do not have an on-board storage tank)
Updated standards are required to permit legal operation at blends above 2% hydrogen 
H
Refuelling station compatibility
Hydrogen fuel content limit
Current hydrogen limit of 2% is in place through consideration of storage tank compliance
New storage cylinder developments and certification required to enable up to 20% hydrogen use.
H
 

Recommended next steps

University of Brighton engine test work indicated that hydrogen blends are not expected to have an adverse effect on performance or emissions at blends of up to 20% hydrogen. However, a number of barriers to commercial operation at these blend levels were identified during this project. The following activities are recommended to address high risk issues:

·        Vehicle tests to confirm the range reduction and also to provide real world validation for project results

·        Verify compatibility of vehicle systems with blends up to 20% through consultation with OEMs

·        Verify compatibility of refuelling systems with blend of up to 20% hydrogen

·        Work with standards bodies to update vehicle and refuelling station standards to permit fuelling with 20% hydrogen blends

Additional recommended next steps are:

·        Consider the implications of the results from this project for the HyDeploy 2 project, for example, perform an initial evaluation of the impact of hydrogen blends on industrial processes (especially those using similar engine and fuel injection systems)

·        Establish an Expert Working Group to lead work in this important area, potentially via the Advanced Propulsion Centre spoke hosted by University of Brighton.

Dissemination

A range of dissemination activities are planned following the end of this project: a journal paper prepared by the University of Brighton team; presentations to Cadent and advisory board stakeholders; presentations at relevant conferences, eg Low Carbon Vehicle Show, Future Powertrain or the SAE International Engine and Vehicles Conference.

·        When available comprehensive details of the Project’s outcomes are to be reported. Where quantitative data is available to describe these outcomes it should be included in the report. 

·        Wherever possible, the performance improvement attributable to the Project should be described. 

·        If the TRL of the Method has changed as a result of the Trial this should be reported.

·        The Network Licensee should highlight any opportunities for future Projects to develop learning further.

Lessons Learnt

The coronavirus pandemic caused closure of the university laboratories for four months at a critical stage of the project, leading to delays both due to the closed period and also due to recommissioning activity that was necessary following facility closure at short notice. These delays are considered to have been unavoidable. However, delays were also experienced due to issues with the test cell and research engine.  The project utilized a newly commissioned single cylinder engine within an existing test cell that had functioned acceptably for the previous research work. Despite this, issues were encountered with both the test cell infrastructure and the single cylinder engine which delayed test work and impacted the modelling work. Lessons learnt were:

·        While the test cell and engine had been successfully run prior to this project, there had been a gap in utilization between this running and the current project. In this time, some obsolescence of equipment had occurred between the previous project and this work. 

o   Lesson learnt: University should improve levels of ongoing maintenance between funded projects to ensure continuing integrity – due to the issues experienced with this project, the research group have implemented bridging funding to ensure that facilities are maintained between periods of use in grant funded projects.

·        Time spent resolving issues was longer than expected, partly due to the complexity of resolving problems with both the test engine and the test cell at the same time.

o   Lesson learnt: Additional contingency should be allowed for engine recommissioning.

·        Fuel was purchased as bottled blended mixtures, which had a lead time of around 4 weeks. A stock of gas was purchased to meet the anticipated needs of the test plan, but it was not always possible to forecast how much gas would be needed, which led to missing test points for some gas blends for particular blends due to project timescales. 

o   Lesson learnt: Factor in gas supply lead time into future test plans