Biodiesel hais txog cov roj ua kua uas tuaj yeem hloov petrochemical diesel, ua los ntawm cov txheej txheem hu ua transesterification siv cov khoom siv raw xws li tsiaj thiab zaub roj, roj microbial, thiab cov roj ua noj pov tseg. Nws pom zoo solubility zoo nrog diesel thiab tuaj yeem siv los sib xyaw lossis ib leeg nrog cov qauv roj diesel. Nws yog ib qho kev huv huv thiab rov ua dua tshiab "ntsuab lub zog" thiab lwm txoj hauv kev zoo tshaj plaws rau cov khoom siv tsis tau txuas ntxiv dua tshiab xws li roj av.
Cov roj zaub uas tsis tau kho kuj tseem tuaj yeem hlawv hauv lub tshuab hluav taws xob, tab sis nws cov viscosity yuav luag 20 npaug siab dua li cov diesel, nrog lub teeb nyem siab heev (siab dua 200 degree). Cov yam ntxwv no ua rau nws nyuaj rau cov roj zaub kom evaporate hauv lub cav diesel, ua rau muaj ntau yam teeb meem. Tom qab ua tiav, xws li kev ua esterification, cov roj zaub tau hloov mus rau hauv biodiesel, nrog rau nws cov khoom siv roj zoo li diesel.
Biodiesel yog cov khoom sib xyaw uas tau muab los ntawm cov tsiaj thiab zaub rog, feem ntau muaj tsib fatty acid methyl esters: methyl palmitate (C16H32O2), methyl stearate (C18H36O2), methyl oleate (C19H36O2), methyl linoleate (C13H32O19) thiab .
Cov methyl esters no muaj cov qauv tshuaj zoo sib xws, nrog rau methyl ester ua haujlwm pab pawg txuas nrog cov saw hlau. Xws li cov tshuaj muaj pes tsawg leeg yog yooj yim dua piv rau petrochemical diesel, thiab nws tsis muaj ntxhiab hydrocarbons thiab feem ntau tsis muaj sulfur. Kev hlawv biodiesel hauv cov cav diesel txo qis emissions ntawm polycyclic aromatic hydrocarbons (PAHs), thaum emissions ntawm sulfur dioxide (SO2) yuav luag xoom.
Hauv cov ntsiab lus, muaj ob qhov zoo rau kev hlawv biodiesel: thawj zaug, nws lub cev thiab cov khoom siv tshuaj lom neeg zoo ib yam li cov roj ntsha ib txwm muaj, thiab qhov thib ob, kev hlawv biodiesel tuaj yeem txo cov pa phem xws li PM, CO, thiab HC los ntawm cov cav tov diesel.