Abstract
This paper describes the potential of existing exhaust emission reduction technologies for diesel engines fuelled with biodiesel. We examined improvements in incylinder combustion technologies using common-rail high-pressure injection equipment, after-treatment technology using diesel particulate filters:DPF and diesel oxidation catalysts (DOC), and fuel treatment technology by the addition of a cetane improver. An additive, 2- ethyl-hexyl-nitrate:EHN, was tested using both neat biodiesel fuel and a 20% biodiesel/ low sulfur gasoil blend:B20 using a DI diesel engine with a common-rail injection system. The EHN was effective for reducing soluble organic fraction:SOF in particulate matter:PM at low engine loads for neat biodiesel fuel. EHN addition reduced NOx for both B20 and gasoil. Engine bench tests and vehicle road tests were conducted using a passive DPF system without a catalyst or electric heater for filter regeneration. For gasoil, regeneration of the DPF was required at approximately 300 km. However, regeneration of the DPF was not necessary when using biodiesel fuel. The DPF is effective for reducing both soot particles and SOF in PM at high and low engine loads. Self-regeneration of the DPF occurs when engine loads change from low to high and when potassium hydroxide catalysts are incorporated into the biodiesel production process; transesterification and refining process. We found that a diesel oxidation catalysts:DOC is effective at reducing SOF, unburned hydrocarbon, carbon monoxide, and aldehydes in exhaust emission.In addition, we devised a strategy for emission control using existing technologies. First, NOx emissions could be reduced by retarding the timing of injection such that it was the same as that of gasoil. This control of timing is particularly important given that the ignitability of biodiesel greater than that of gasoil. SOF in PM will be reduced by DPF, DOC and cetane improver at low engine loads. In general, soot emission associated with biodiesel is less than that of gasoil because biodiesel is oxygenated and free of aromatic hydrocarbon diesel fuel. Furthermore, soot emission can be suppressed by high-pressure injection and DPF, while the gaseous exhaust emissions, CO, HC, and aldehydes, will be reduced by DOC. Finally, the combination of conventional emission control technologies, DPF, DOC, fuel additives, will necessitate high-pressure injection in order to meet the stringent diesel engine emission targets for biodiesel-fuelled diesel engines by 2010.
Keywords: Biodiesel, Diesel Particulate Filter, Oxidation Catalyst, Additives, Common- Rail High-Pressure Injection