ENGINEERING FOR RURAL DEVELOPMENT Jelgava, 26.-28.05.2021. 1236 EXPERIMENTAL PROBLEM OF INDIRECTLY DETECTING ENGINE TORQUE DELIVERED BY AGRICULTURAL MACHINES THROUGH EXHAUST GAS TEMPERATURE Marco Bietresato, Francesco Selmo, Massimiliano Renzi, Fabrizio Mazzetto Libera Universita di Bolzano, Italy marco.bietresato@unibz.it Abstract. Measuring the performance of the compression-ignition internal combustion engine of agricultural machines (in particular, the torque delivered instantaneously) is an essential requirement for monitoring: (a) the exploitation of the engine mechanical-energy potential (in terms of generated torque) and (b) its correct operation (in terms of global efficiency, fuel consumption and possible ageing). Due to the many important technical and economic implications, the instant acquisition of the engine torque is therefore a critical point in any operational monitoring system, as well as in predictive maintenance models. Torque measurement is by no means a simple task, especially in old agricultural machines lacking of default data acquisition devices/on-board electronics, and many critical issues arise from the fact that it involves rotating components (shafts), which are often difficult to be accessed. For this reason, an indirect torque measurement methodology, based on a predictive model relying on the exhaust gas temperature, is preferable. An accurate measurement of temperature data is of primary importance to precisely calculate the torque, which means performing an accurate thermocouple choice, placement, and data elaboration. This is made even more challenging by the fact that the temperature of the exhaust gas is often in a transient state due to variable engine regime necessary for machine operation. The study presented here illustrates some considerations about the trend and the equation of the experimental measurements of the exhaust gas temperature, considering three different positions for the thermocouples on the exhaust line, and proposes an optimal technical solution in terms of sensitivity and promptness of response. Keywords: farm machinery, diesel engines, engine performance, fuel gas temperature, temperature sensor position, Newton’s equation. Introduction Nowadays agricultural machines give a fundamental and unavoidable support to human work, both in developed and in developing countries, and the production of a sufficient amount of food (at economically- and environmentally-sustainable conditions) is unthinkable without the utilization of these machines [1; 2] Unfortunately, a large amount of these vehicles is very old, especially (but not only) in developing countries, due to a generalised low replacement rate. Just to give some examples, more than one half of the circulating agricultural machines in Italy (estimated to be about 2 100 000 units) are more than 20 years old, and around 30% of the total circulating machines are more than 33 years old [3; 4]. The use of these out-of-date vehicles may cause many problems related to safety, pollutant emissions, reliability, performance decay and maintenance (that are also linked to decreases in productivity). However, what makes things even more complicated on old machines, is the absence of sensors or other modern apparatuses able to give the users some information about the previously listed issues. Having reliable data would allow to implement some optimization strategies, to reduce possible problems, ruptures and so on, thus bringing to effective benefits. This is the reason why a data acquisition system placed on these machines would be of great importance [5]. In this context, the exhaust gas temperature (EGT) is one of the most meaningful parameters that can be monitored, as it can provide information about the torque, combustion quality, pollutants [6-9]. The correlation between the EGT and the torque is proven [10-13] with the most approximated equation that gives a linear correlation between these two quantities. However, more elaborate models can give a dependence also from the rotational regime [14]. In each case, many studies often correlate EGT and torque during stationary operating conditions for the engine (i.e., at constant values of engine rotational speed or torque), but very little information could be found on what happens during operative transients between one engine regime to another one, or with different levels of torque to be delivered. It is worth noting that the torque applied by a vehicle engine during its working day can change many times, depending on the tasks to be performed, so the EGT measured at the exhaust is often in a transient status caused by even-sudden load changes. Due to the presence of many materials involved in the transmission of heat from the exhaust gas to a possible temperature probe, the measured temperature can be temporarily misaligned with the effective EGT. This means that a possible change in the measured temperature does not follow instantaneously a change of the applied torque; even in stationary conditions DOI: 10.22616/ERDev.2021.20.TF271