Blended Hydrogen and Compressed Natural Gas for Transport

Blended Hydrogen and Compressed Natural Gas (CNG) for Transport was a project commissioned by Cadent, the UK’s largest gas distribution network, who are working to decarbonise the UK natural gas supply by blending hydrogen in the UK natural gas network.

To meet 2050 targets for reduction of GHG emissions, significant progress is required in both heat and transport sectors. Cadent’s HyNet programme seeks to address this challenge in both sectors through the addition of hydrogen to the gas network.

Existing projects address commercial arrangements for this development and the impact on CHP applications however evidence examining the impact of this activity on transport is currently incomplete.

Reducing GHG emissions, and in particular improving air quality became a UK Government imperative following Climate Earth ruling. While electrification has been expected to provide a useful route to decarbonisation of passenger transport, electrification of heavy duty vehicles is challenging due to high power and range requirements. Consequently, this sector is generally recognised as one of the most difficult to decarbonise.

One of the options seeking to address these challenges is methane fuelled engines which are gaining market share for heavy duty vehicles due to perceived benefits in reducing fuel costs, emissions and noise.

This project aimed to deliver evidence of the impact of plans to introduce hydrogen into the gas fuels on heavy duty transport by developing fundamental understanding of the influence of varying concentrations of hydrogen on combustion in heavy duty, methane powered Euro VI engines.

Previous work in this area had mainly focused on light duty engines, with analysis of the performance of heavy duty engines fragmented and generally unrepresentative of current Euro VI engines. Development of evidence of the performance of these engines on methane/hydrogen blends will reduce risk associated with the Hynet project through providing evidence of likely acceptability for the transport sector. Along with complementary NIA studies, this work will produce data sets that can be used to support the definition of new acceptable network standards/limits (current standard 0.1%mol of hydrogen).

The overarching objective of the project was to provide evidence of the impact or introducing hydrogen in the gas supply on natural gas fuelled transport applications, especially methane engines used in HGVs.

The project had a number of task-orientated sub-objectives;
1. Review the 'state of the art' for hydrogen/methane dual fuelling in the heavy duty on road sector
2. Commission a single cylinder engine at UoB which Is representative of a Euro VI dedicated SI gas engine
3. Develop evidence of the impact of hydrogen on methane fuelled engine operation when used in heavy duty, on road applications through single cylinder engine test and modelling
4. Provide guidance on the potential hydrogen limit that should be considered regarding use of natural gas/hydrogen blends in gas engine transport/heavy freight vehicle applications
5 Identify barriers to use of natural gas and hydrogen blends In heavy duty on road applications and develop understanding of fut\Jre technology developments that may be required to enable use of high hydrogen blends.

The project output also informed HyNet, HyNet Motion, HyPurity and HyDeploy NIC projects In relation to potential hydrogen content limits

The Blended Hydrogen and Compressed Natural Gas for Transport project investigated these aims through research into the impact of hydrogen/methane blends on transport users through a single cylinder test and analysis of combustion of methane/hydrogen blends in Euro VI truck engines.

An initial literature 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.

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 were 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.

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 utilised 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.