###### Abstract
Preliminary internal results at Aramco show that by running low octane gasoline (RON80) on a custom engine mounted on a D class vehicle, it is possible to improve the fuel economy by up to 30%, enabling low temperature combustion while having vehicles that are compliant with drivability targets [18; 19]. Nevertheless, the simultaneous introduction of a new fuel and a new engine into the market poses lot of  
Figure 1: GCI pathway towards fuel and engine co-optimization. challenges, and two possible routes to reach this end goal are considered. The first solution, called Engine Matched to the Fuel, commercial gasoline is combusted in a modified CI engine while in the second one, called Fuel Matched to the Engine, the ignitibility properties of gasoline are modified to be able to be used in a market-available diesel engine [20, 21]. The Fuel Matched to the Engine GCI vehicle variant was showcased by Aramco in the summer of 2018 (international congress SIA powertrain in Rouen and international powertrain, fuels and lubricants meeting in Heidelberg). By running CN35 (RON45) in a recalibrated Peugeot 308, it was possible to decrease the CO2 emissions by 7% (vs. the original diesel engine) while complying with Euro 6d emissions standards. The Engine Matched to the Fuel GCI variant is still under development at Aramco. Preliminary results have shown CO2 emissions that are similar to the ones of a diesel engine. The engine showed the possibility of reducing the BSFC by 22% and 11% versus a TGDI and diesel engine, respectively, at 1500 rpm and 6 bar of IMEP (indicated mean effective pressure). Hybrid electric vehicle (HEV) technologies are one of the most active areas in research and development in the automotive industries. The degree of hybridization can vary from minor vehicle stop-start systems to complete vehicle redesign. A fully hybrid vehicle could reduce fuel consumption by up to 30% at an estimated price increase of up to USD 9000 per vehicle depending on vehicle size [22]. This paper suggests different HEV configurations in terms of different battery size and HEV hardware scenarios using GCI-based ICEs. GCI engines have the potential to achieve high efficiency and to significantly reduce both nitrogen oxides (NOX) and particulate matter (PM) emissions by operating under diluted and partially premixed conditions. An ongoing developmental problem with GCI engine technology is controlling the combustion process throughout the engine operating range. The combustion timing can be easily adjusted by changing the spark event and perhaps the fuel delivery for conventional gasoline SI engines, and the fuel injection timing and fuel injection amount for conventional diesel CI engines. However, it is not nearly so easy to control the GCI combustion process. Depending on the fuel's auto-ignition quality (such as research octane number, RON, and CN) and the engine hardware configuration (such as compression ratio, CR), the GCI engine operation strategy map can be typically classified into different combustion models. This paper will address the different combustion models of GCI engines with three fuels (CN15, CN25, and CN35) compared to diesel (CN53), and hybrid vehicle simulations are then used to assess the potential of the gasoline compression ignition (GCI) engines with different hybrid architectures.