## 1 Introduction  
The transport sector contributed the second-highest amount to global carbon dioxide (CO2) emissions in 2023, representing slightly more than 21% [1]. About 15% of total carbon is CO2 from passenger cars and vans in the European Union (EU), which significantly contributes to climate change [2, 3]. The transport sector is the only one that emits more greenhouse gases than in 1990, but with the application of additional measures, the amount of transport emissions could be 5% lower in 2030 [4]. Within the EU, vehicular traffic continues to be the primary contributor to emissions originating from the transport sector. In 2022, it represented 73.2% of all EU greenhouse gas emissions from domestic and international transport. The average CO2 emissions from new passenger cars and vans registered in the EU has also continued to decrease in 2023 by 1.4% for cars and 1.6% for vans compared to 2022 levels. In general terms, preliminary estimates point to a small reduction of 0.8% in total EU transport greenhouse gas emissions from 2022 to 2023 [5, 6]. Inorder to meet the EU's goals for reducing greenhouse gas emissions, intermediate emissions reduction targets have been set until 2030: 55% less pollution for cars and 50% for vans compared to 2021, and from 2035, all new passenger cars and vans in the EU would emit zero carbon dioxide [7]. Transportation is regarded as a highly promising field where the amount of harmful emissions can be significantly reduced [8; 9], especially related to internal combustion engine emissions using alternative liquid and gaseous fuels: ethanol, methanol, butanol, methane, biomethane, biogas, or natural gas [10; 11; 12]. Also, the rapidly growing popularity of hybrid, fuel cell, and electric cars is making a significant contribution to reducing greenhouse gas emissions [13]. Modern internal combustion engines (ICEs) are equipped with variable valve timing (VVT) systems to improve their environmental and energy performance [14; 15]. This enables the precise control of the intake and exhaust valves, adjusting to various engine operating conditions. In VVT systems, the intake valve closing (IVC) time is one of the main parameters that indicates the exact point, defined as degrees after bottom dead center (aBDC) at which the intake valve closes [16]. Moreover, IVC adjustment is predicted to reduce harmful emissions, enhance fuel efficiency, and increase power output [17]. Delaying IVC results in a substantial decrease in particle number (PN), approximately 95.4% and 98.2% for 5 nm and 23 nm particles, respectively [18]. Furthermore, conducted real-world driving emissions tests show that compressed natural gas (CNG) vehicles exhibited significantly lower particle number emissions compared to gasoline counterparts, even without the use of a particulate filter [19]. The LIVC strategy enhances both brake-specific fuel consumption (BSFC) and brake thermal efficiency (BTE) due to the increased expansion ratio, which facilitates the more efficient extraction of work from the piston [20]. There is a reduction in BSFC by 6.7% under minimum fuel usage conditions, coupled with a ~10-11% decrease under high loads when utilizing the Miller cycle with LIVC, compared to the original Otto cycle [21]. However, delaying IVC can also have adverse effects on engine performance, especially under low-load conditions. Applying delayed LIVC in an SI engine fueled by a combination of producer gas, biogas, and hydrogen resulted in slightly higher BSFC due to due to lower cylinder charge volume as well as a diminished amount of combustible air-fuel (A/F) charge. This suggests that delaying IVC might negatively impact BSFC in natural gas engines, at least under certain conditions [22]. LIVC can also improve combustion stability, especially in engines operating with NG at low load. This improvement was attributed to the increased turbulence and better mixing of the air-fuel mixture resulting from LIVC [23]. In gasoline engines, LIVC can help mitigate knock, which can limit engine performance and efficiency [24].