The performance of a 118-kW tractor fuelled by pure biodiesel was monitored during a long-term field experiment with\ud approximately 800 h of engine function. The objective was to demonstrate that B100, a pure biodiesel fuel, is a viable alternative to\ud traditional diesel oil in terms of long-term mechanical reliability. A bench test on the new engine, performed by attaching a test stand to\ud the power take-off of the tractor, showed an expected reduction in power (–9%) and torque (–7%) and an increase in specific consumption\ud (+13%) when biodiesel was used as a complete substitute to diesel oil. Furthermore, with the same setup, the exhaust gas had a Bosch\ud smoke index equal to 50% of the value for the same engine fuelled with diesel oil. After these initial tests, the tractor was set up for\ud normal field operations, in which both the engine curves and lubricant quality were periodically monitored. These surveys indicated\ud no significant reduction in engine performance; however, the lubricant was consequently diluted and contaminated by biodiesel, which\ud caused the lubricant properties to considerably worsen. However, on the basis of the chemical–physical analysis, reducing the oil\ud change interval from 200 h (manufacturer’s indications for the engine when operating with diesel oil) to 100 h would compensate for\ud this progressive quality decline. At the end of the trials, the engine was disassembled to check the condition of its components; wear\ud and lacquer-like coating phenomena were observed, and their levels were acceptable. The obtained results demonstrated that B100\ud can effectively substitute for diesel oil in a standard compression-ignition engine: the power change is not perceptible during normal\ud operation of a tractor, and no particular problem will arise in the engine during its life if the lubricant is changed every 100 h

Rotary drum dryers operating in co-current mode are commonly used for drying food and feed in leaf form, reducing the damage caused by the high air temperatures typical of these dryers, as well as providing advantages including reduced drying times and increased energy efficiency. However, drying control to ensure a desirable product exit moisture content is strongly based on empirical practices, which are usually jealously guarded by producers and users, grounded in simplified mathematical modelling. To overcome these uncertainties, in this work, a more complete mathematical modelling approach, based on the solution of ordinary differential equations (ODEs), is developed. The ODEs describe the drying process in the drum dryer, where the air is continuously cooled and humidified as the product dries. The mathematical model developed was experimentally verified in a drum dryer by drying alfalfa, and the maximum relative error was found to be only 2.4%. Finally, a comparison between the complete model proposed here and a simplified model was conducted, using both for drying control to keep the product exit moisture content constant (i.e., at 0.111). The results indicated that the simplified model provided values of air inlet temperatures erroneously higher, up to +8.2%, with a consequent higher energy consumption, lower dried alfalfa quality, and a greater risk of fire, given that the product exit temperature was dangerously increased.

The mathematical modeling presented in this work concerns the conveyor-belt dryer with the tangential flow of air with respect to food. This dryer, if operating in co-current, has the advantage of well preserving the organoleptic and nutritional qualities of the dried product. In fact, it has a low air temperature in the final stretch where the product has low moisture content and is therefore more temperature sensitive. It is a bulkier dryer than the continuous through-circulation conveyor dryer with a perforated belt. The latter is therefore more frequently used and has received greater study attention from researchers and designers of the industry. With the aim to propose guidelines for a rational design of the conveyor-belt dryer with tangential flow, a mathematical model was developed here through the differentiation of the drying rate equation followed by its integration performed along the dryer belt. Consequently, and with the assumption that the final moisture content X_F of the product is higher than the critical moisture content X_C, the relationships between the intensive quantities (temperatures, humidity and enthalpies), the extensive quantities (air and product flow rates) and the dimensional ones (length and width of the belt), were obtained. Finally, on the basis of these relationships, the rules for an optimized design for X_F > X_C were obtained and experimentally evaluated.