The need for the decarbonization of heavy-duty vehicles requires a deep understanding about the effects of biofuels, which represent a viable pathway to cut the emissions in the hard-to-abate sectors, like agricultural tractors. A novel meta-analysis approach can help to thoroughly investigate the effects of biodiesel blends on farm tractor engines in terms of performance and emissions. Studies were identified using the main keywords related to internal combustion engines in prominent scientific databases. Standardized mean differences were calculated for each study to evaluate engine performance and gas emissions. Mixed-effects regression models were developed to investigate performance and environmental pollution changes over different biodiesel blending ratios, biodiesel sources, and engine types. The analysis revealed significant effects of biodiesel blending ratio on decreasing torque [−13.0%, CI 95% (6.7%–19.3%); I2 = 97.67; p = 0.000; Q = 129.94], engine power [−15.0%, CI 95% (10.0–20.0%); I2 = 54.82; p = 0.000; Q = 101.81], CO2 emissions [−24.1%(15.0–32.0%);
I2 = 0.198; p = 0.000; Q = 20.04], and CO emissions [−17.5%, CI 95% (16.0–18.0%); I2 = 98.62; p = 0.000; Q = 97.69], while increasing specific fuel consumption [+5.2%, CI 95% (1.0–9.0%); I2 = 95.94; p = 0.000; Q = 129.74] and NO emissions [+11.0%, CI 95% (6.0–15.0%); I2 = 98.51; p = 0.000; Q = 157.56]. The same analysis did not show any influence of the sources of biodiesel and the engine type. Finally, meta-regression found a significant positive association between increasing ratios of biodiesels and decreasing torque, engine power, CO and CO2 emissions, and increasing fuel consumption and NO emissions in terms of linear equations. Although through these equations it is not possible to individuate an optimal range of blending ratios able to lower the emissions and not affect the engine parameters, the range from 9.1% to 13.0% of biodiesel is a good tradeoff. Within it, the only decrease in engine performance is in charge of the power, however contained within 4%, while CO and CO2 emissions are reduced (respectively by 0.0%/−2.8% and −3.6%/−6.0%) without using any specific pollutant abatement systems.

Energy production relies on finite fossil fuels and is usually regarded as the primary source of hazardous emissions and global warming. As a result, much attention has been dedicated to biofuel as a fuel for engine alternatives. Biofuel is now primarily utilized in blends with fossil diesel. As a result, this study was focused on adding bioethanol and biodiesel to fossil diesel. Biodiesel was manufactured by transesterification from waste cooking oil, while bioethanol was made through banana fermentation. The physical properties such as density, kinematic viscosity, flashpoint, and cetane index of fossil diesel-biodiesel-bioethanol blends were compared with fossil diesel fuel in laboratory experiments. When added, bioethanol was found to degrade the physical properties of blended fuels substantially. The substitution of bioethanol for fossil diesel resulted in a significant reduction of hazardous emissions. The assessment of flue gas emissions indicated a considerable reduction in CO2, CO, hydrocarbon (HC) and NOx emissions.

Biofuels represent an environmental-friendly and feasible alternative to fossil fuels for internal combustion engines. The use of diesel-biodiesel-bioethanol fuel blends (ternary blends) is one of the most interesting solutions in terms of fossil fuels substitution. They provide an improvement of exhausts gas emissions without any significant sacrifices in terms of energy-conversion efficiency. However, engine operation may be affected by the fuel substitution especially in the auxiliary mechanical fuel-feed systems, traditionally designed for low-density and high-viscosity fossil fuels. In the proposed work, two easy-to-use experimental-based mathematical models have been obtained by using the response surface method to assess the behaviour of fuel feed-pumps when biofuels blends are used. Density and mass flow-rates have been measured for several fuel mixtures and at different temperatures. The proposed equations are intended to be used as a practical tool, based on the optimal behaviour of the fuel feed-pump, in order to choose the best ternary fuel-mixture composition and/or predict/infer the engine performances under non-tested conditions (i.e., other mixtures’ compositions and temperatures, however within the inquired domain).

The fuelling of internal combustion engines with biofuels has certainly many environmental and energetic advantages. These advantages are particularly effective in the agricultural sector, where an integrated biofuel supply-chain would further benefit the overall carbon balance. Unfortunately, there are also some drawbacks, mainly concerning the engine performances (lowering of the torque curve), but also environmental (possible raising of the NOx emissions). However, by appropriately mixing two biofuels with known opposite effects on the combustion process, it is theoretically possible to compensate the aforementioned disadvantages. In this work, some experiments were carried out in this direction by fuelling a farm tractor with four different fuel mixes; the collected data were processed through the Response Surface Methodology to obtain multi-parameter regression equations useful to identify the optimal fuel mixtures composition. Thanks to this approach, it was found that biodiesel has a positive effect on the torque, while the addition of bioethanol has a much bigger detrimental effect; on the contrary, bioethanol should be added to a mixture with a minimum of 8-12 % of biodiesel to get advantages in terms of NOx concentration reduction.