## 2 Materials and Methods  
### Experimental Setup (Fuels and Engines)  
CN25 and CN35, straight run gasoline, are a generic term describing the fraction of crude oil that boils within the 30-180 \({}^{\circ}\)C range. It is composed of C5 to C11 hydrocarbons and has a low research octane number (RON) value. In addition, it is a refinery product that can potentially be beneficial to reduce the CO2 footprint from well-to-tank as an example of a less processed fuel. CN fuels are only processed in crude atmospheric distillation towers and undergo light hydro-desulfurization, which is in contrast to commercial diesel, which is derived from various deep conversion process units including hydrocracking, a highly energy-intensive and costly process dedicated to converting heavier streams from vacuum distillation into blending stock for the diesel and jet fuel pools. From the perspective of reducing CO2 emissions from tank-to-wheel, compared to diesel fuel, CN fuels also present intrinsic benefits. Indeed, CN25 and CN35 have a higher H/C ratio along with a higher energy content per mass unit (LHV) that directly leads to the CO2 reduction benefits of these fuels. A summary of the fuel properties is in Table 1. Depending on the straight run gasoline cut, the latter might be expected to be around 3.5%, assuming that it has the same engine efficiency. CN35 autoignition properties lie in an intermediate position within the range delimited by CN15 and diesel fuel. Compared to diesel, the tested CN fuels have lower kinematic viscosities and a reduced lubricating capability. An amount of 1000 ppmof additives (Paradyne) were added to improve the lubricity of the test fuels for the fuel injection system.  
The Table 2 represents the specification of engines and nozzle. The engine for the CN fuel tests was equipped with a variable geometry turbocharger (VGT) and a high-pressure loop (HPL) EGR system. The engine was controlled by an open ECU to control the air loop and injection set points from map or specific user dictated values. The hydraulic flow rate (HFR) of the nozzle for the CN fuels was increased to 340 cc/30 s/10 MPa. Compared to the diesel baseline, the 340 cc flow rate compensates for the lower fuel density. The engine provides a full-rated power of 88 kW at 3500 rpm and a maximum torque of 300 Nm at 1750 rpm. For all of the experiments, the emissions were logged once per second for 60 s after a stabilization period, and the average of those 60 recordings are what is presented in this paper. At the same time, the in-cylinder pressure was recorded for 250 cycles. The average of pressure data used for the calculation of IMEP and COV_imep (below 3%_Coefficient of Variation_IMEP) was also considered for all of the results in this study. Regarding the errors of the experiments, the errors are less than 0.5 mm for the fuel spray penetration measurement and up to \(\pm\)2.5% for the error range of the brake thermal efficiency (\(BTE\)) for the HEV simulation (Equation (1)):  
\[\frac{\Delta BTE}{BTE}=\sqrt{\left(\frac{\Delta Torque}{Torque}\right)^{2}+ \left(\frac{\Delta N}{N}\right)^{2}+\left(\frac{\Delta qmfuel}{qmfuel}\right)^ {2}+\left(\frac{\Delta LHV}{LHV}\right)^{2}} \tag{1}\]  
where \(N\) is engine speed (rpm), and \(qmf\) is mass flow of injected fuel.