A computational study of the use of hydrogen peroxide as pilot fuel for a homogeneous mixture of ammonia/hydrogen in a compression ignition engine

Tingas, Efstathios-Alexandros; Hardalupas, Yannis; Taylor, Alexander M. K. P.

Abstract

We report a computational investigation of a compression ignition (CI) engine (compression ratio: 17.6, displacement volume: 1.3 L) where the main fuel is a homogeneous mixture of ammonia (70-60% vol%) and hydrogen (30-40% vol%), with a global equivalence ratio varying between 0.44 and 0.5, depending on the H2/NH3 ratio. The novelty of this study is that it employs a pilot injection of hydrogen peroxide to initiate ignition, without the use of any air or charge preheating (the temperature/pressure at intake BDC are 330 K/1.4 atm, representing mild boost an defficeint intervooling). Hydrogen peroxide (H2O2) has the attributes that it can be produced from renewable sources, and it is already widely manufactured, distributed, and stored, with diverse applications (as an aqueous solution of H2O2 with shares up to 30 vol%). The main advantage of using H2O2 as pilot fuel, as opposed to other more conventional ones (e.g., diesel), is that it contains no carbon, and hence produces no CO2 and particulate matter (PM). The computational investigation was conducted with an advanced commercial stochastic engine model that has been previously validated. The investigation was primarily focused on assessing the effects of using hydrogen peroxide in aqueous solution as pilot fuel on engine efficiency, combustion phasing and NOx emissions. These three aspects were investigated over a range of engine speeds (750-1,750 rpm) in view of: (i) the variation of the mass of the directly injected (DI) aqueous solution (0.1-10 mg); (ii) the variation of the H2O2 share (15-50%) in the directly injected (DI) aqueous solution; (iii) the variation of the start of injection (from -20 to -4 CAD aTDC) and injection duration (1-8 CAD). There is a strong effect of the peroxide in advancing combustion timing (CAD50 is advanced by up to 15 CAD) and in decreasing combustion duration (CAD90-CAD10 decreases up to 10 CAD), and peroxide readily enables medium engine loads which are the ones investigated in this work. Indicated thermal efficiencies above 50% were readily achieved at all engine speeds and, with a 30 vol% peroxide share in the solution, the pressure rise rate was always below 30 bar/ms. However, the NOx emissions in all cases exceeded the IMO’s Tier III standard. Possible ways to tackle this would be either the use of exhaust gas recirculation, or optimisation of the injection strategy, or the use of aftertreatment. For most cases, on a volume basis, the required aqueous H2O2 amount is 3% of the main fuel while on an energy basis this translates to 1.1% of the main fuel blend. The results reported in this initial study are promising because it is possible to ignite a premixed charge on the basis of a small pilot volume of commercially available hydrogen peroxide solutions.

Citation

Tingas, E.-A., Hardalupas, Y., & Taylor, A. M. K. P. (2024). A computational study of the use of hydrogen peroxide as pilot fuel for a homogeneous mixture of ammonia/hydrogen in a compression ignition engine. Journal of Ammonia Energy, 2(1), 42-63. https://doi.org/10.18573/jae.28

• Journal Article Type: Article
• Acceptance Date: Apr 8, 2024
• Online Publication Date: Jul 4, 2024
• Publication Date: 2024
• Deposit Date: Jul 17, 2024
• Publicly Available Date: Jul 17, 2024
• Electronic ISSN: 2752-7735
• Publisher: Cardiff University Press
• Peer Reviewed: Peer Reviewed
• Volume: 2
• Issue: 1
• Pages: 42-63
• DOI: https://doi.org/10.18573/jae.28
• Keywords: zero-carbon engine; hydrogen peroxide; ignition promoter; CI engine; heavy-duty engine.