## 1 Introduction
Several studies have been carried out to demonstrate the potential of the RCCI strategy addressing single-cylinder [21], multi-cylinder [22], heavy-duty [23], medium-duty [24], and light-duty diesel engines [25] operating with low [26], medium [27], and high [28] compression ratios (CR). In general, the results demonstrated that operation in stationary conditions results in NOx levels that are below the limits proposed by the emissions regulations, together with ultra-low soot emissions [29]. Despite the advantages of this combustion mode, common issues of the LTC modes are also present, such as high amounts of unburned HC and CO emissions during the low engine load operation [30], and excessive pressure rise rates (MPRR) and in-cylinder maximum pressure peaks (P\({}_{\text{max}}\)) at high loads. Therefore, the RCCI operation is still restricted to moderate loads inside the engine map [31]. Some approaches have been investigated to overcome these issues and complete the engine map whenever the RCCI is unable to run properly. The low level of geometric and hardware modifications allow switching the combustion mode to, typically, CDC [32]. Nonetheless, such a strategy is difficult to justify from a technological standpoint. The RCCI/CDC dual mode can only be attractive to the transport industry if the fuel consumption versus single CDC and the cost of the required after-treatment systems needed to surpass the emissions regulations are reduced. For this purpose, the RCCI operation in the global engine map should be maximized [33]. Despite the improvements in the combustion area, achieving the normative values constraints is still a challenge. In this sense, electrification becomes more and more frequent in the OEMs in order to reduce the total CO\({}_{2}\) emitted by their fleet. Approaches such as fuel cell vehicles are also extensively investigated, demonstrating a capability to reduce the vehicle emissions to almost zero [34; 35]. Detailed information can be found in [36; 37]. Regarding electric vehicles, different concepts such as Mild, Series, and Parallel hybrid vehicles can be found as options in the market, and much research has been developed addressing their utilization. The use of high-efficiency cycles such as the Atkinson cycle [38] and low-temperature modes are a major research focus. Regarding the LTCs, their typical application is found in series architecture due to the simplicity of the implementation and working points of view. Previous numerical studies demonstrated that the operation using RCCI combustion can reduce up to 9% of the total fuel consumption compared to a hybrid spark ignition (SI) engine [39]. In addition, experimental investigations demonstrated that the SHV can reach normative values for emissions by implementing appropriate design changes [40]. For this architecture, the charging strategy and the number of operating conditions used to charge the engine were found to have fundamental importance. [PERSON] et al. [41] stated that as the number of operating conditions is increased, better fuel consumption is achieved. However, the same authors recognized that the number of starts of the internal combustion engine during the cycle and the transition between the different operating conditions should be taken into account. As a general conclusion, all the authors state that the use of RCCI combustion in a series concept should improve the fuel consumption values. However, the conclusions regarding emissions on driving cycles are difficult to find in the literature. The objective of this work is to evaluate the benefits of the hybrid architecture with the internal combustion engine (ICE), studying the RCCI combustion mode compared to conventional modes operating in diesel and dual-mode combustion. Experimental steady maps from fuel consumption and emissions were measured in a test bench for a high CR light-duty diesel engine (17.1:1) and are used as boundary conditions to estimate the transient performance of the vehicle.