To get accurate indicator diagrams without the use of pressure transducers, the strain and the displacement of the various parts of engine structures that would have some relationship with the pressure variation in the cylinder were measured and analyzed mathematically.
By measuring the strain of the cylinder head bolts, the horizontal displacement of the crank shaft end, and the vertical displacement of the intake valve stem, we realized that the indicator diagrams could be obtained easily without a passage from the interior to the outside of the combustion chamber.
Accurate indicator diagrams were estimated by applying the pressure-strain diagram obtained from the static pressure test in the cylinder to the strain variation in the cylinder head bolts. On this occasion, the accuracy of the estimated indicator diagrams could be improved by providing the cylinder head system with a one degree freedom vibration system. The propriety of this measuring method was examined and proved in the experiments.
This method can be applied not only for single cylinder engines, but also for multi-cylinder engines.