Investigating anode off-gas under spark-ignition combustion for SOFC-ICE hybrid systems

Abstract

Solid oxide fuel cell – internal combustion engine (SOFC-ICE) hybrid systems are an attractive solution for electricity generation. The system can achieve up to 70% theoretical electric power conversion efficiency through energy cascading enabled by utilizing the anode off-gas from the SOFC as the fuel source for the ICE. Experimental investigations were conducted with a single cylinder Cooperative Fuel Research (CFR) engine by altering fuel-air equivalence ratio (ϕ), and compression ratio (CR) to study the engine load, combustion characteristics, and emissions levels of dry SOFC anode off-gas consisting of 33.9% H2, 15.6% CO, and 50.5% CO2. The combustion efficiency of the anode off-gas was directly evaluated by measuring the engine-out CO emissions. The highest net-indicated fuel conversion efficiency of 31.3% occurred at ϕ = 0.90 and CR = 13:1. These results demonstrate that the anode off-gas can be successfully oxidized using a spark ignition combustion mode. The fuel conversion efficiency of the anode tail gas is expected to further increase in a more modern engine architecture that can achieve increased burn rates in comparison to the CFR engine. NOx emissions from the combustion of anode off-gas were minimal as the cylinder peak temperatures never exceeded 1800 K. This experimental study ultimately demonstrates the viability of an ICE to operate using an anode off-gas, thus creating a complementary role for an ICE to be paired with a SOFC in a hybrid power generation plant.

Investigating realistic anode off-gas combustion in SOFC/ICE hybrid systems: mini review and experimental evaluation

“…On that note, the Discussion section included rigorous correlations, between the current and aforementioned sections. In general, the reviewed hybrid systems operated mostly on NG, as was observed in all, 7,13,18,22,25,26,31–35,37–41 and across a variety of mixture concentrations. Moreover, hydrogen was examined in dual fuel operation with diesel, 21 as was methanol.…”

“…In that, maximum net indicated fuel conversion efficiency ( η f , in ) of 31.2% was achieved for a CR of 13:1 with a ϕ of 0.9, whereas NO x and soot emissions were justified negligible. Ran et al 39 additionally investigated operating the same apparatus at CRs of 9:1, 11:1 and 13:1 (SI), with variable water vapor content, ranging from 0 to 50%. Net fuel conversion efficiency peaked at 31.3% for the latter CR, combustion efficiency was maximized at 97% for the former CR, while water vapor content over 30% significantly deteriorated operation.…”

“…All identified research articles classified under different modes of combustion (MoCs) involving SI, SAI, HCCI, and RCCI, as adapted from. 13,18,22,25,26,[31][32][33][34][35][36][37][38][39] intermittency issues, linked to popular renewable energy (RE) technologies, such as wind turbines (WTs) and photovoltaic (PV) panels, are being dealt with hybridization with SOFC subsystems. Therefore, the particular type of systems should probably be favored over aforementioned stand-alone RE practices, at least in terms of stable and uninterrupted operation.…”

“…In detail, multiple modes of combustion were considered, enhancing system flexibility in operation, among which the most dominant was identified in homogeneous charge compression ignition (HCCI). 13,18,22,25,26,[31][32][33][34][35] Other modes involved all spark ignition (SI), [36][37][38][39] spark-assisted ignition (SAI), 18 as well as reactivity-controlled compression ignition (RCCI). 13 Evidently, low temperature combustion (LTC) was extensively assessed, with the majority of researchers investigating leaner mixtures, 22,25 as illustrated in Figure 1 and in certain cases across multiple compression ratios (CRs).…”

“…All identified research articles classified under different modes of combustion (MoCs) involving SI, SAI, HCCI, and RCCI, as adapted from. 13,18,22,25,26,31–39 …”