Study on thermal management strategy of the exhaust gas of diesel engines based on in-cylinder injection parameters 2020-01-0621
Due to high thermal efficiency, reliability and durability, less fuel consumption, and less carbon dioxide (CO2) emission, diesel engines are widely used in both stationary and mobile applications. However, an inherent combustion mode of diesel engines results in harmful emissions like hydrocarbons (HC), carbon monoxide (CO) and particulate matter (PM), the emissions can cause substantial damage to the human health and environment, so there are strict emission regulations to limit the harmful emissions. Diesel oxidation catalyst (DOC) and diesel particulate filter (DPF) are important exhaust gas aftertreatment devices to oxidizing the HC, CO and PM in order to meet the requirements of emission regulations. However, emission regulations become more stringent, the test procedure has been changed from New European Driving Cycle (NEDC) to Worldwide Harmonised Light Vehicle Test Procedure (WLTP), most of the test operating conditions in the WLTP are under medium and low engine loads, so the temperature of exhaust gas of diesel engines is relatively low during the whole WLTP cycle. For the exhaust gas aftertreatment system, especially for the regeneration process of DPF, the high temperature requirement will distinctly affect its regeneration efficiency, so DOC is generally set before DPF to rise temperature by oxidizing HC and CO, the temperature of DOC outlet is very important for the regeneration progress of DPF. But for DOC itself, the oxidation process also needs a certain light-off temperature, which can’t be satisfied under medium and low engine loads conditions in the WLTP, so the thermal management of exhaust gas is critical for the WLTP.
This study proposes a novel thermal management strategy of exhaust gas of diesel engines. In the experiment, the influence of post injection parameters and throttle opening of diesel engines on the temperature of exhaust gas were studied. Besides, the effect of late post injection parameters of diesel engines on the temperature of DOC outlet was also studied.
The results show that reasonable control of throttle opening, injection pressure, injection timing and injection amount of post injection can significantly increase the average temperature of exhaust gas from 237.8 ˚C to 333.6 ˚C, an increase of 40.3%. Reducing the main injection pressure can slightly increase the temperature of exhaust gas, but the PM significantly increases and the fuel economy deteriorates. Delaying main injection timing also increases the temperature of exhaust gas slightly, so it’s not suitable for the thermal management of exhaust gas. Besides, with the delay of late post injection timing, CO emissions firstly increase and then decrease, while HC emissions keep increase, and the increasing rate reaches the highest value between 60°and 90° CA ATDC. The increase of injection amount of late post injection also increases the concentration of CO and HC, and the temperature of DOC outlet increases sharply, but the amount should be controlled reasonably to avoid lubricating oil dilution in the cylinder.