A 22:1 Compression Ratio Ammonia-Hydrogen HCCI Engine: Combustion, Load, and Emission Performances

Abstract

The interest in ammonia as a high-density hydrogen carrier for long-term electricity storage is growing. A clean and efficient Combined Heat and Power (CHP) system is envisioned for power production from stored ammonia, to which Homogeneous-Charge Compression-Ignition (HCCI) engines are promising. Although recent preliminary studies showed a high equivalence ratio potential for ammonia HCCI engines, its resistance to auto-ignition forces the use of high intake temperatures, which limits the (still unknown) ammonia-HCCI power density. Moreover, the feasibility of clean and highly efficient ammonia combustion has not been demonstrated. To give a first complete insight on these various aspects, an HCCI test bench has been modified to ammonia-hydrogen operation through the use of a 22:1 effective compression ratio. A cartography of the ammonia-hydrogen load range, related efficiencies and emissions is obtained following the impact of the ammonia fuel blending ratio (from 0 to 94%), equivalence ratio (from 0.1 to 0.6), intake temperature (from 50 to 240 • C) and Exhaust Gas Recirculation. Thanks to a reduced combustion intensity, ammonia allows a 50% IMEP increase compared to neat hydrogen, while maintaining equivalent combustion efficiencies. Neat hydrogen performances were not impacted from the high compression ratio. Fuel-NO X emissions have been observed, and linearly increasing with the ammonia flow rate up to 6,000 ppm, although the EGR led to a three-fold reduction of those. Still EGR negatively impacted NO 2 and unburned emissions. Below combustion temperatures of 1,400 K the production of N 2 O is suspected and 1,800 K are needed to ensure complete bulk ammonia combustion. Finally, the trade-off for the ideal ammonia-hydrogen blending ratio is discussed. As perspectives, extensive work is needed on fuel-NO X primary reduction measures and after-treatment ways. Regarding primary measures, this work suggests that boosted conditions with maximized stroke-to-bore ratios should be aimed at, to allow higher EGR rates at maintained combustion temperatures.

The Influence of Hydrogen on Vaporization, Mixture Formation and Combustion of Diesel Fuel at an Automotive Diesel Engine

“…The increase of the combustion intensity at Hydrogen use, reflected in the decrease of fuel droplets combustion duration, Figure 7, and increase of flame radius, Figure 8, is in correlation with the increase of maximum pressure and of maximum pressure increase rate at this operating regime with 13% and 29%, respectively [1]. Similar aspects are shown in other research papers [12][13][14][15][16][17][18][21][22][23][27][28][29][30].…”

“…The increase of the combustion speed assures the increase of the flame radius at Hydrogen-diesel fuel fueling, Figure 8, with 3.8% at the maximum xc. Different research papers present pressure and heat release diagrams analysis, which show the reduction of combustion duration at Hydrogen use [14,15,[19][20][21][22][23][27][28][29], which is related to the decreasing tendency in combustion time at H2 use, Figure 7. Hydrogen combustion leads to the acceleration of the flame developing, the maximum radius of the flame developed around the fuel droplet being registered with 3 °CA sooner on the combustion cycle compared to xc = 0.…”

“…Pochet [29] observes for a diesel engine that, if Hydrogen is used, compared to diesel fuel or to ammonia NH 3 , the combustion starts sooner per cycle and the combustion period is reduced, but the maximum heat release rate decreases from 4.5 (at 92% vol. NH 3 ) to 1.6 (at pure H 2 ).…”

The Role of Electrofuels under Uncertainties for the Belgian Energy Transition

“…In this sense, further investigations shall address the case of ammonia. Given its advantages (e.g., carbon-free hydrogen-carrier, existing infrastructure), this molecule looks to be an attractive solution as an energy-carrier for power applications [67], when used as dual fuel with hydrogen or methane [5,6] or to defossilise the freight transport sector (e.g., maritime transport) [68,69]. However, many challenges remain regarding its synthesis, its uses and applications (i.e., in a combustion engine or in a fuel cell), or even its environmental impact [70].…”

“…Development on electrofuels aims at making them more and more compatible with existing and mature technologies [4]. An example is carbon-free ammonia-hydrogen blends burned in spark ignition engines [5] or combined heat and power (CHP) applications [6]. With a growing share of VRES, sector coupling is essential to absorb the surplus of electricity from these intermittent production means [7] and integrate them more cost-effectively [8,9].…”