Abstract
In a century of car engine development, only two processes were subject to automatization: air-fuel mixture ratio and spark advance angle. Therefore, it is obvious that going even further with automatization of another two engine parameters, such as compression ratio and intake valve(s) lift, will lead to improved performances.
The paper presents an engine concept, which continually adjusts the compression ratio and intake valve lift, depending on the drive situation, thus the engine is operating at an optimum point for every driving condition. This engine is an intrinsec, automatic self-regulation system with fast response time and in the same time it is a natural development of the classic engine. It is entirely designed and experimented in its main functions.
The paper presents one particularity of this hinged engine concept ¡V variable squish height through the rotary motion of the upper block. Other particularities of this engine concerning its variableness has to be also mentioned here: induced variable valve timing also through the rotary motion of the upper block, variable valves overlap and duration through the thermal valves clearance, which together with the two main variable systems for compression ratio and variable intake valve lift entitle the right of this engine concept for the adaptive thermal engine name.
The squish motion at the adaptive thermal engine is a consequence of the combustion chamber configuration (a 2 valves wedge combsution chamber) and the paper¡¦s goal was to prove the variable squish motion intensity at this engine is actually favourable. In the case of the adaptive engine, the intensity of the radial motion is variable because the squish height is also variable. Thus, at idle operation (CR=12.5) the squish height is minimum (lTDC=1mm), and then it increases with load, attaining at wide-open throttle the maximum value (lTDC= 4 mm), when CR8.5. Imposing of high radial speed is interesting for any working regime, but especially for those corresponding with part throttle, where combustion time is rather big, thus a reduction of this being obtained. The numerical results had the following interpretation: the adaptive engine operates with a minimum value for squish height exactly when it¡¦s necessary, thus resulting a turbulence intensity increasing, which represents better condition for burning process at idle and part load (it has to be said these working regimes are with high frequency in the engine operation). Towards high loads and speeds, clearance between piston head surface and cylinder head (lTDC) increases, but in this case the decreasing of radial speed is not considered a drawback because the mixture speed through the valve gate is high enough to produce turbulence and good combustion. The variable squish height also imposes taken into consideration of convective heat transfer. The calculation regarding this issue also revealed a better operation of the adaptive thermal engine in comparison with the classical engine from whom the design was started. Obviously, the variable squish motion is complex enough, thus further investigation would be needed.
Taking into account that actual mass production combustion chambers are of hemispherical-open kind (without bumping areas), the authors have provided the adaptive thermal engine with such a solution, too - a 2 valves per cylinder cross flow cylinder head.