Instantaneous Crank Speed Variations as Related to Engine Starting 850482

Typically, engines with relatively few cylinders have required higher cranking speed to start in low temperature ambients. Of the several factors that contribute to cold startability, this study has focused on the instantaneous speed variation of the engine during cranking. This theoretical computer study revealed that engines slow substantially during compression and that the lengthening of compression time is exaggerated as the number of cylinders is reduced. It is hypothesized that long compression time creates excessive heat and blowby losses. In turn these produce low compression temperatures and pressures, hence greater difficulty in igniting the charge especially under cold cranking conditions were average engine speed is low, By matching the compression times of various engines designs, the relative average speeds required to start can be predicted with reasonable accuracy.