## 1 Introduction
[15] revealed the central role of engine calibration, pilot injection, and rail pressure to optimize the benefits of ethanol towards emissions minimization and higher thermal efficiency in CI engines. Similarly, [PERSON] et al. [16] allocated the pressing need for research on advanced injection systems as a concrete driver of CO2 emissions targets in the future state of ICEs while maintaining high power density. [PERSON] et al. [17] elaborated on recent advances that integrate gasoline partially premixed combustion in Euro 5 diesel engines. The study focused on describing the effects of appropriate calibration parameters, pilot quantity, and exhaust gas recirculation to maximize thermal efficiency and reduce global pollutants. On the other hand, hydrogen technology gradually becomes a prominent candidate as an energy carrier that can promote an enhanced operation in both CI and SI engines based on environmental and operational perspectives. Hydrogen production is primarily led by gas reforming technologies representing nearly 60% of the global production [18]. Nonetheless, the carbon footprint of reforming-based production schemes features several challenges to contribute to greenhouse emissions minimization. Therefore, the role of hydrogen production via water-splitting and biomass technologies will be of increased interest in the mid-long term of the hydrogen market [19]. The continuous research on electrolyzers has facilitated the construction of sophisticated and feasible components that maintain proper operation, high-purity reactant agents, and reasonable production rates [18; 19; 20]. Therefore, since water electrolysis produces hydrogen and oxygen, the gaseous fuel enrichment in ICEs can be performed either with standalone hydrogen operation and hydroxy gas (HHO). [PERSON] et al. [21] experimentally evaluate the influence of hydrogen doping from 5% to 25% in a single-cylinder. Increasing hydrogen replacement increases the incylinder pressure while minimizing both HC and CO emissions; however, the adverse effect of such implementation was the intensification of NOx formation. [PERSON] et al. [22] envisioned HHO enrichment as a secondary fuel in SI engines encountering promising results towards enhancing thermal efficiency and power output and decreasing emissions. [PERSON] et al. [23] revealed that a constant volumetric HHO enrichment in the engine triggers adverse effects in power output, fuel consumption, and emissions levels. Therefore, the authors implemented a hydroxy control unit to control the volumetric rates of gaseous fuel replacement via voltage and current variations to guarantee the optimal rate based on the engine operation. In this way, they managed to reduce fuel metrics, overall emissions and enhance thermal performance. The main contribution of this investigation is to evaluate the performance of the dual-fuel operation in spark ignition (SI) engines while simultaneously implementing hydroxy (HHO) gas enrichment and acetone-butanol-ethanol (ABE) as additive. The study incorporates evaluation metrics based on combustion performance, thermal efficiency, fuel consumption, and emissions levels. The novelty of this paper relies on the incorporation of a complete methodology to predict combustion performance and energy/exergy distributions. This study examines a combined fuel operation mode in SI, which has not drawn sufficient attention in published studies. In the development of the experimental assessment, ABE is used in different volumetric ratios, namely 5% (ABE 5) and 10% (ABE 10), whereas hydroxy gas is implemented as gaseous fuel in volumetric flow additions of 0.4 LPM. Moreover, the study includes a complete characterization of the experimental test bench, hydroxy generation system, instrumentation, and measuring uncertainty. Therefore, this work represents a further effort on closing the knowledge gap in the implementation of alternative fuels in SI engines while pinpointing experimental and numerical guidelines to evaluate the performance of dual-fuel technologies.