Tuning of Valve Timing with AVL-GCA for Full Load Enhancement across the Whole Speed Range

The most important goal in engine development for racing is the reduction of lap times. In order to be able to exert a noticeable influence in this area, it is not sufficient just to increase the peak performance. The whole full load curve has to be optimised. The torque provided by the engine is highly dependent on the degree of charging. That is, the amount of air in the cylinder at intake valve closure (IVC). This can be quantified by the volumetric efficiency η_vol.

Figure 1: Pressure Characteristics Cam Shaft 1

Figure 2: Pressure Characteristics Cam Shaft 2

For naturally aspirated engines, the valve lift can have a significant influence on the volumetric efficiency. The variation of the intake and exhaust timing is mainly limited by racing regulations. Therefore, it is even more important to thoroughly examine the opening times across the complete speed range. That is, accurate determination and adjustment for ideal operation.

Figure 3: Valve Lift* - Figure 4: Mass Flow*

*Camshaft 1 – Dashed Line, Camshaft 2 – Solid Line

AVL-GCA can be used for better understanding of phenomena such as scavenging or intake backflow which play a decisive role in the degree of charging. Due to the combination of the “measurement tool” AVL-GCA and the simulation tool AVL-BOOST, the engineer can reduce the number of test variants, resulting in reduced development times. The measurements of the variants camshaft 1 and camshaft 2 driven on the test stand clarify this process; they show the corresponding pressure curves (intake, cylinder and exhaust) that were determined during operation with these two different camshaft profiles (Figures 1 to 4).

For camshaft 2 a larger valve overlapping time can be seen than for camshaft 1, resulting in an increased scavenging mass flow and thus an increased filling. A higher volumetric efficiency in combination with faster energy conversion leads to a higher maximum pressure p_max, which leads to the desired increase of torque.

Figure 5: Pressure Curve - Figure 6: Combustion Process and Combustion Function

*Camshaft 1 – Dashed Line, Camshaft 2 – Solid Line

When examining high-speed racing engines AVL-GCA provides high accuracy with regard to the combustion analysis and represents a reliable tool for the evaluation of parameter variations and their effects on the entire process.

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