| Abstract [eng] |
As fuel prices continue to fluctuate and environmental regulations become increasingly strict, vehicle manufacturers and users are increasingly seeking ways to improve vehicle fuel economy while simultaneously reducing their environmental impact. Ground clearance (the vertical distance from the bottom of the vehicle to the road surface) is one of the many factors influencing aerodynamic drag and, consequently, fuel consumption. However, there is a notable lack of comprehensive studies in scientific literature that quantitatively evaluates the impact of ground clearance on fuel consumption under real-world operating conditions. The theoretical part of the master's thesis explores the principles of automotive aerodynamics, discussing airflow dynamics around a moving vehicle and analyzing the sources of aerodynamic drag and their influence on vehicle efficiency. Existing studies found in the literature, which investigate the effect of ground clearance on aerodynamic characteristics, are reviewed, and the methodology of Computational Fluid Dynamics (CFD) application, along with aerodynamic coefficient calculation processes, is detailed. The literature review identified that although aerodynamic elements, such as spoilers and diffusers, are commonly used in vehicle design, the influence of ground clearance is typically discussed only at a theoretical level. There remains a lack of experimental and numerical studies that would evaluate the direct impact of ground clearance on fuel consumption. In the research part of the thesis, a numerical analysis was conducted using SolidWorks and ANSYS Fluent software. A 3D model of the vehicle was created and examined with three different ground clearance configurations – 110 mm, 130 mm, and 150 mm – and at three speeds – 90, 110, and 130 km/h. After determining aerodynamic drag coefficients and drag forces, theoretical fuel consumption values were calculated by evaluating changes in vehicle resistance. The calculations showed that reducing ground clearance by 20 mm decreased the drag coefficient at all tested speeds. At 90 km/h, the drag coefficient decreased from 0.291 to 0.281 (around 3.4% reduction), at 110 km/h from 0.287 to 0.278 (around 3.1%), and at 130 km/h from 0.285 to 0.274 (around 3.9%). Larger differences were observed when reducing ground clearance by 40 mm (from 150 mm to 110 mm), with the drag coefficient reductions recorded at all speeds: from 0.291 to 0.269 at 90 km/h (around 7.6% reduction), from 0.287 to 0.266 at 110 km/h (around 7.3%), and from 0.285 to 0.262 at 130 km/h (around 8.1%). Based on the theoretical calculations, it was determined that a 20 mm reduction in ground clearance results in approximately a 1.6–2.2% decrease in fuel consumption, while a 40 mm reduction achieves approximately a 3.5–4.6% decrease. In the experimental part of the study, real-world tests were conducted using an external fuel supply system to precisely measure the amount of fuel consumed independently from the vehicle’s ECU readings. The experimental results confirmed the trends observed in the numerical analysis – as ground clearance decreases, fuel consumption also decreases. At a speed of 90 km/h and a ground clearance of 150 mm, a fuel consumption of 4.55 l/100 km was recorded, while at a clearance of 110 mm, consumption dropped to 4.18 l/100 km (approximately an 8% reduction). At higher speeds, the differences became even more pronounced: reducing the clearance by 40 mm (from 150 mm to 110 mm) at 130 km/h resulted in fuel consumption decreasing from 6.6 l/100 km to 6.0 l/100 km, approximately a 9% reduction. Furthermore, reducing ground clearance by 20 mm (from 150 mm to 130 mm) also showed a noticeable 3–5% reduction in fuel consumption across all tested speeds: from 4.55 to 4.38 l/100 km at 90 km/h (approximately 3.7%), from 5.3 to 5.1 l/100 km at 110 km/h (approximately 3.8%), and from 6.6 to 6.28 l/100 km at 130 km/h (approximately 4.8%). These findings confirm that even a 20 mm reduction in ground clearance can save 3–5% in fuel consumption, while a 40 mm reduction results in savings exceeding 8–9%, especially at higher speeds. It was also noted that although experimental results were slightly higher due to environmental factors, the overall consistency between the numerical and experimental results demonstrates strong correlation between the two methods. The last part of the paper compares the results of experimental tests and theoretical calculations and makes recommendations. It is noted that although the experimental results are slightly higher, the overall consistency between the calculations and the experimental results shows a good correlation between the two methods. This confirms that as the ground clearance decreases, the fuel consumption of vehicles decreases. |
