There are many advantages in utilizing biofuels in respect of conventional ones in Internal Combustion Engines (ICEs). Thanks to their particular chemical-physical structure, biofuels burn cleaner than fossil fuels, reducing the emissions of CO and Particulate Matter (PM), this last especially in Diesel engines. They don't produce sulfur or aromatics, so there's no unpleasant smell associated with burning biofuels. They still release greenhouse gases like carbon dioxide but do so at reduced levels. According to a report by the National Renewable Energy Laboratory (NREL), biofuels produce roughly 75% fewer carbon dioxide emissions than petroleum fuels since CO₂ emitted during combustion is successively re-absorbed by the plant (from which they are obtained) during growth. In addition to these environmental benefits, biofuels can also give economic advantages to the territory where the waste matrices are obtained (circular economy). As every non-conventional fuel, the behaviour of the new ester biofuels
(HexHex-based and FAEEs) must be analysed (as they are or blended with conventional fuels) on a test engine to verify their compatibility with the engine requirements in terms of performance, exhaust emissions and combustion characteristics. Following a realistic assessment of the quantities available, the possible use of biofuels must be seen mixed (in appropriate volume percentages) with conventional fuels. Therefore, an extensive engine testing campaign will be carried on utilising the experimental apparatus of the Department of Energy, System, Territory and Construction Engineering (DESTEC) of the University of Pisa. In particular, the chemical-physical characteristics of the biofuel have to be preventively analysed and compared to conventional fuels. After that, several blends with conventional fuel will be prepared and tested on the experimental engine. Previous experiences, utilising advanced biofuels for Diesel engines obtained from lignocellulosic materials, have proven the possibility of blending these new biofuels up to 20% (by vol.) with conventional Diesel fuel without significantly altering engine performance and obtaining a drastic reduction in particulate emissions.
Engine performances will be evaluated analysing the following parameters (with the relative measurement equipment):
- experimental engine constituted by a Lombardini-Kohler LD 625/2 direct injection Diesel engine;
- engine torque and power and at different engine speeds and loads utilising a Borghi&Saveri eddy current dynamometer;
- specific fuel consumption with AVL fuel balance;
- soot emissions with a Smoke Meter (AVL 415 S), which determines the Filter Smoke Number (FSN) according to ISO 10054: a volume of exhaust gases is collected and flows through a paper filter; then, a photo electric cell measures the light absorption through the paper filter and determines the filter blackening;
- exhaust gases composition with a gas analyser which includes a NDIR (Non-dispersive Infrared Detectors) Analyser for CO, CO₂, O₂ concentration; a Flame Ionization Detector (FID) for the concentration of HC; a Chemiluminescent analyser to measure of the concentration of NO_x.
Parallel to this, the pressure signal in the combustion chamber will be acquired using an acquisition system consisting of a Kistler 6052/B pressure transducer, a Kistler charge amplifier, an AVL encoder and an AVL Indimiter data acquisition system with Indiwin software for data analysis. The acquired in-cylinder pressure signal, after appropriate mathematical elaborations, will give valuable information on engine combustion timing and stability, thus allowing to analyse the behaviour of the various mixtures in different engine operating conditions.