Characterisation of Knock in Direct Injection Hydrogen Internal Combustion Engines

The internal combustion engine (ICE) has been the 'silver bullet' in powering machinery for the transportation, mining and construction industries. However, with existing and upcoming regulations on CO2 emissions, the industry is exploring the viability of fuelling ICEs with hydrogen as a carbon neutral alternative - notable examples include BMW, Toyota, Yamaha and JCB.
Current hydrogen combustion research focuses on achieving high brake thermal efficiency (greater or equal 45%) while keeping NOx emissions levels low by utilising direct injection fuelling strategies. This results in increased volumetric efficiency and allows for a more precise control of abnormal combustion events compared to port fuel injection. Nevertheless, topics such as combustion irregularities, turbocharger design for hydrogen-specific operation, heat transfer and injection strategy optimisation remain underresearched.
The main goal of this research project is to improve the state-of-the-art knock modelling for hydrogen ICEs in a 1D simulation environment - namely GT-Power, by creating computationally inexpensive knock models and validating them against experimental data. At present, there is a single fast-running commercially available knock model developed by GT, which is based on a neural network trained with hydrogen ignition delay times using the kinetics mechanism developed by Keromnes et al. (2013). This model offers approx. 16 times quicker simulations compared to a H2/02/NOx kinetics mechanism. However, it suffers from several limitations - (1) it is based only on the chamber pressure, temperature and recirculated exhaust gases, but does not account for the presence of different knock-inducing species such as NOx molecules and radicals in the unburned zone of the working fluid; (2) It is based on a now-outdated kinetics mechanism, current state-of-the-art mechanisms include Konnov (2019), Polimi (2020), Kovacs et al. (2020) and Sun et al. (2022) ; (3) in comparison to previous knock models developed for gasoline engines, this model cannot be quantified using mathematical equations based on the Arrhenius equation. Therefore, at present this project aims to deliver new knock models created using the current state-of-the-art kinetics mechanisms. These will be based on neural networks, similar to GT's proprietary knock model, but also accounting for the presence of knock-inducing nitrous oxides, as well as on the Arrhenius equation, which expands on previous gasoline-specific models and includes terms for the recirculated exhaust gas and NOx concentrations. The following actions have been identified:
1. Conduct a literature review on the topic of knock in ICEs with a focus on hydrogen ICEs and applications of kinetics mechanisms.
2. Assess the pathways to creating neural network-based models and Arrhenius equation-based models.
3. Develop neural network-based models and explore their predictive accuracy against simulations using the detailed kinetics mechanism and validate them using empirical data.
4. Develop Arrhenius equation-based knock models and compare against detailed chemical kinetics and experimental data.
The potential benefits of this project are significant improvements to the computational time of 1D ICE simulations, while retaining the knock prediction accuracy of the state-of-the-art knock models. This will ultimately lead to increased engine thermal efficiency and reduced calibration times, as the knock-limited spark advance can be better predicted prior to engine testing.

Impact Summary

This proposal has been developed from the ground up to guarantee the highest level of impact. The two principal routes towards impact are via the graduates that we train and by the embedding of the research that is undertaken into commercial activity. The impact will have a significant commercial value through addressing skills requirements and providing technical solutions for the automotive industry - a key sector for the UK economy.

The graduates that emerge from our CDT (at least 84 people) will be transformative in two distinct ways. The first is a technical route and the second is cultural.

In a technical role, their deep subject matter expertise across all of the key topics needed as the industry transitions to a more sustainable future. This expertise is made much more accessible and applicable by their broad understanding of the engineering and commercial context in which they work. They will have all of the right competencies to ensure that they can achieve a very significant contribution to technologies and processes within the sector from the start of their careers, an impact that will grow over time. Importantly, this CDT is producing graduates in a highly skilled sector of the economy, leading to jobs that are £50,000 more productive per employee than average (i.e. more GVA). These graduates are in demand, as there are a lack of highly skilled engineers to undertake specialist automotive propulsion research and fill the estimated 5,000 job vacancies in the UK due to these skills shortages. Ultimately, the CDT will create a highly specialised and productive talent pipeline for the UK economy.

The route to impact through cultural change is perhaps of even more significance in the long term. Our cohort will be highly diverse, an outcome driven by our wide catchment in terms of academic background, giving them a 'diversity edge'. The cultural change that is enabled by this powerful cohort will have a profound impact, facilitating a move away from 'business as usual'.

The research outputs of the CDT will have impact in two important fields - the products produced and processes used within the indsutry. The academic team leading and operating this CDT have a long track record of generating impact through the application of their research outputs to industrially relevant problems. This understanding is embodied in the design of our CDT and has already begun in the definition of the training programmes and research themes that will meet the future needs of our industry and international partners. Exchange of people is the surest way to achieve lasting and deep exchange of expertise and ideas. The students will undertake placements at the collaborating companies and will lead to employment of the graduates in partner companies.

The CDT is an integral part of the IAAPS initiative. The IAAPS Business Case highlights the need to develop and train suitably skilled and qualified engineers in order to achieve, over the first five years of IAAPS' operations, an additional £70 million research and innovation expenditure, creating an additional turnover of £800 million for the automotive sector, £221 million in GVA and 1,900 new highly productive jobs.

The CDT is designed to deliver transformational impact for our industrial partners and the automotive sector in general. The impact is wider than this, since the products and services that our partners produce have a fundamental part to play in the way we organise our lives in a modern society. The impact on the developing world is even more profound. The rush to mobility across the developing world, the increasing spending power of a growing global middle class, the move to more urban living and the increasingly urgent threat of climate change combine to make the impact of the work we do directly relevant to more people than ever before. This CDT can help change the world by effecting the change that needs to happen in our industry.