Waste plastic oil (WPO) derived from pyrolysis of plastic debris and municipal waste is one of the promising alternative fuels because of its similar carbon chain characteristics and physical properties to diesel fuel. WPO also contains naphtha which is gasoline-like and may not be well-suited to a diesel engine. Technically, naphtha should be eliminated from WPO by distillation, and the resulting product is called distilled waste plastic oil (WPOD). This work experimentally investigates the influences of these fuels burned in a diesel engine on combustion characteristics and exhaust gas emissions. Both WPO and WPOD fuels contribute to the larger amount of nitrogen oxides than diesel fuel. Carbon-based emissions increase when the engine operates with these pyrolysis fuels by retarding the ignition onset of their combustion occurrences. Meanwhile, their shorter-carbon-chain links provide a lower smoke index. However, brake thermal efficiency and brake specific fuel consumption are beneficial because of their high calorific value and cetane index.

An experimental study of the particulate matter (PM)-related emissions from the combustion of waste cooking oil (WCO)-based biodiesel-blended (0%, 30%, and 100% v/v) fuels in a four-cylinder diesel particulate filter (DPF)-equipped engine was carried out. A laboratory-scale DPF under the controlled conditions was installed into an aftertreatment system, and the PM mass and number characteristics were investigated. The combustion analysis based on in-cylinder pressure shows that the added WCO shortened the ignition delay, advanced the combustion ignition, and increased peak pressure values compared to conventional diesel fuel. The WCO increase in specific fuel consumption led to a slight reduction in brake thermal efficiency. The WCO-fueled engine showed reduced PM and total unburned hydrocarbon but increased nitric oxide emission. The nucleation and accumulation were characterized for nanoparticle number and size distribution. The particle number (PN) concentration in total was declined to smaller values when fueling with WCO. In the thermogravimetric analysis, the PM of WCO oxidized to a greater level than that of diesel fuel, which was observed by the weight loss rates during the specified heating program. WCO lowered the elemental carbon (EC) part of PM than diesel fuel. When equipping an exhaust system with DPF, the EC and the total PN drastically reduced while the particle size slightly increased. The use of DPF with the WCO biodiesel mitigated both EC and organic carbon components of the captured particles of the released PM.

The utilization of biodiesel as an alternative partial replacement of diesel fuel was shown to improve exhaust emissions from diesel engines. Waste cooking oil biodiesel (WCO) has also gained more attention due to edible biofuel supply and the environment. In this study, a nonthermal plasma (NTP) technique was applied to be equipped into the after-treatment system of a four-cylinder diesel engine at medium- and high-load conditions. The exhaust gases in the NTP state from the combustion of WCO and diesel (D100) fuels were partially drawn by spectrometers and nanoparticle-number-derived characteristics were analyzed. The particle number, area, and mass concentrations were in log-normal distribution over equivalent diameters, and they were higher at high load. The concentration of the particulate matter (PM) was lower but was larger in size when the NTP charger was activated due to coagulation principally owing to WCO’s number and surface area. The total particle masses were lower for WCO at the two load conditions tested. During NTP charger activation, the mass mean diameters were increased by maximum values of 24.0% for D100 and 5.5% for WCO. The PM removal efficiencies were maximized by 10.8% for D100 and 16.7% for WCO when the NTP charger was in use, and the WCO exhaust was dominantly seen to simultaneously reduce NO_x and PM emissions.