A simple, cheap and effective way of measuring the pressure inside the cylinders of internal combustion engines is proposed in this paper. It is well known that the in-cylinder pressure is one of the most significant variables describing the combustion status in internal combustion engines; therefore, if the measured value of the actual pressure in the combustion chamber is used as a feedback variable for closed loop monitoring and control techniques, it will be possible both to improve engine performances and to reduce fuel consumptions and emissions. However, to date such a pressure-based control strategy has been limited by costs, reliability and lifetime of commercially available cylinder pressure sensors.
To overcome these limitations, the present paper proposes a very simple and low cost experimental device for measuring the pressure inside the combustion chamber, developed for engine control and monitoring applications. The sensor exploits the strain measurements of the external walls of engine cylinders, which are indicative of the pressure information during the combustion process. The measurement is carried out by means of strain gauges attached to the external wall of the cylinders inside the water channels of the cylinder block. This location has been selected because it minimizes the temperature variations induced by different loads and engine speeds.
This study presents a feasibility analysis of the system. Preliminary tests were initially conducted on a hydraulic cylinder and subsequently on an internal combustion engine. The analysis shows that the proposed method has the potential to predict the internal cylinder pressure accurately, thus representing an interesting contribution for the development of low-cost engine management systems. The robustness of the proposed solution has the potential to be very high, as the concept is based on strain gauges. Forthcoming experimental investigations on a fired engine under regular engine operating conditions will aim at assessing the capability of the proposed method over various loads, frequencies and thermal conditions.