Experimental study on ammonia/hydrogen/air combustion in spark ignition engine conditions

Abstract

8The mitigation of climate change implies the increasing use of variable renewable energy sources. Energy 9 storage and transport solutions will contribute to ensure the stability, reliability and flexibility of the energy 10 systems in that context. Ammonia is a well-known chemical of formula NH3 and, amongst other electrofuels, 11 a promising energy carrier and carbon-free combustible fuel. In the present experimental study, engine per-12 formance, combustion characteristics and pollutant emissions of a recent spark ignition engine fueled with 13 premixed ammonia/hydrogen/air mixtures were assessed. Gaseous ammonia blends in a wide range of hydro-14 gen fuel fractions and equivalence ratios were tested at two different engine loads. Results show performances 15 comparable with conventional fuel operation when the appropriate promotion strategies are used. Specifically, 16 blending up to 20% hydrogen in the fuel by volume improves the cyclic stability and avoids misfires, while 17 granting the best work output and indicated efficiencies near stoichiometry. Higher hydrogen fractions result 18 in depleted efficiency, attributed to higher wall heat losses. The combustion duration is directly correlated to 19 the LBV of the mixtures, thus being accelerated by hydrogen blending. The accelerating effect of hydrogen is 20 particularly remarkable during the initial stage of the combustion. Hydrogen appears therefore mainly as an 21 ignition promoter. Increasing the engine load improves the furnished work and allows to extend the operating 22 boundaries in terms of mixture composition. 23 48 risk of engine knock thanks to the high octane number of ammonia. This was demonstrated in early studies, 49where single-cylinder and multi-cylinder SI engine were successfully run on pure ammonia fuel [17][18][19]. 50However, gasoline-like performances were only achieved by using one or several promoting strategies, in-51 cluding an improved ignition system, increasing the engine load or CR and H2 doping of the NH3 fuel. A 52 minimum H2 amount depending on the engine speed and CR of some percent by mass was necessary to ensure 53 satisfying performance and decrease NH3 emissions but at the cost of increased NOx emissions. 54Contemporary studies also investigated ammonia/gasoline fueling of SI engine, either to reduce carbon-based 55 emissions of gasoline engines, or to promote the combustion with ammonia as a main fuel. Granell et al. 56proposed a 70% NH3 / 30% gasoline blend by energy as a good trade-off at full load in a Collaborative Fuel 57 Research (CFR) engine [21,22]. The authors suggested supercharging the engine instead of increasing the CR, 58 due to the detrimental thermodynamic consequences of the early spark advance required by the NH3 fuel. 59Engine-out NH3 emissions proportional to the NH3 input are reported, up to 22000 ppmvw for stoichiometric 60 NH3/air at CR=10:1. Ryu et al. investigated direct gaseous NH3 injection in a CFR engine (CR = 10:1) with 61 gasoline as the base fuel, and reported acceptable performance ...

Combustion Characteristics of Ammonia in a Modern Spark-Ignition Engine

“…The set-up is introduced in the dedicated section in the following. The first part of the study aimed at determining the satisfying limits of operation of the present engine in its as-is design in terms of mixture composition and was presented in [29]. Premixed gaseous ammonia/hydrogen/air mixtures with up to 60 vol.% H2 in the fuel were fueled in the engine for equivalence ratios ranging from 0.6 to 1.2.…”

“…The experiments with NH3/H2/air mixtures show that H2 mainly acts as an ignition promoter during the initiation phase when small fractions are added [30]. Further enrichment then significantly accelerates the combustion phases, as the effect of hydrogen on the combustion properties is becoming more important [29]. Therefore, the assumption of partial thermal NH3 dissociation to H2 and N2 in the fresh gases under the combined effect of the compression and the spark could explain the successful engine operation with pure NH3, in spite of unfavorable combustion properties.…”

Modeling of the Combustion Process in a Diesel Engine

“…At the moment, there are quite a lot of studies in the field of reducing harmful emissions of internal combustion engines, these include mixing hydrogen fuel [1,3,10,12], using modern water injection control systems [2], swirling the flow [4], diluting various types of fuel with liquefied gas [5] or methane [6], diesel [7], catalysis [8], gas recirculation [9], "poor" burning [11].…”

Aqueous solution of ammonia as marine fuel

“…Pochet et al 17 reported on engine experiments using ammonia and hydrogen mixtures in Homogeneous Charge Compression Ignition (HCCI) combustion mode. Lhuillier et al 18 recently reported engine experiments of ammonia and hydrogen mixtures under spark-ignition engine conditions. Ammonia has also been demonstrated in modern compression ignition engines in combination with conventional diesel fuel oil, used for ignition.…”