Comparison on Combustion and Emissions Performance of Biodiesel and Diesel in a Heavy-duty Diesel Engine: NO _X , Particulate Matter, and Particle Size Distribution

Low carbon emissions policies for the transportation sector have recently driven more interest in using low net-carbon fuels, including biodiesel. An internal combustion engine (ICE) can operate effectively using biodiesel while achieving lower engine-out emissions, such as soot, mostly thanks to oxygenate content in biodiesel.

This study selected a heavy-duty (HD) single-cylinder engine (SCE) platform to test biodiesel fuel blends with 20% and 100% biodiesel content by volume, referred to as B20, and B100. Test conditions include a parametric study of exhaust gas recirculating (EGR), and the start of injection (SOI) performed at low and high engine load operating points. In-cylinder pressure and engine-out emissions (NOX and soot) measurements were collected to compare diesel and biodiesel fuels. Exhaust particulate matter (PM) emissions were collected to assess solid particle mass and particle size distribution (PSD) using a micro-soot sensor (MSS) and a Cambustion different mobility spectrometer (DMS500), respectively.

Fuel consumption was higher with B20 and B100 than with diesel. However, soot emissions were reduced significantly with biodiesel fuels. B20 and B100 also have lower PSD curves, which indicates a smaller total particle count at a given mobility diameter (ranging from 6 nm to 1000 nm). PSD of all fuels shows a well- known bimodal characteristic. A slight difference in nitrogen oxides (NOX) emissions was observed and could be due to the difference in the physio-chemical properties of biodiesel and diesel fuels. Engine-out emissions of carbon monoxide (CO) and unburned hydrocarbon (UHC) are lower with biodiesel fuels than diesel.

High-speed combustion analysis suggests that minor modification in injection strategy is potentially needed for biodiesel fuels to deliver a diesel-like combustion profile, as seen by the apparent heat release rate (AHRR) curve. Overall, findings from current study suggest the drop-in capability in modern diesel engines of biodiesel with similar diesel-like efficiency and lower PM emissions.