Abstract
The effects of two pilot injections on combustion and emissions were evaluated in a single−cylinder turbocharged diesel engine, which operated in premixed charge compression ignition (PCCI) modes with multiple injections and heavy exhaust gas recirculation under the low load by experiments and simulation. It was revealed that with the delay of the start of the first pilot injection (SOI−P1) or the advance of the start of second pilot injection (SOI−P2), respectively, the pressure, heat release rate (HRR), and temperature peak were all increased. Analysis of the combustion process indicates that, during the two pilot injection periods, the ignition timing was mainly determined by the SOI−P2 while the first released heat peak was influenced by SOI−P1. With the delay of SOI−P1 or the advance of SOI−P2, nitrogen oxide (NOx) generation increased significantly while soot generation varied a little. In addition, increasing Q1 and decreasing the second pilot injection quantity (Q2) can manipulate the NOx and soot at a low level. The advance in SOI−P2 of 5 °CA couple with increasing Q1 and reducing Q2 was proposed, which can mitigate the compromise between emissions and thermal efficiency under the low load in the present PCCI mode.
Highlights
With increasing concerns about fossil fuel consumption, environmental protection, and stricter emission regulations, the production of engines urgently needs higher fuel conversion efficiency and lower emissions
It can be found that the second peak pressure and maximum heat release rate (HRR) increased with delaying
The effects of two pilot injection timings and injection ratios on the emission and combustion using pilotpilot-main injection strategy under the high exhaust gas recirculation (EGR) rate of 44% and low indicated mean effective pressure (IMEP) of 0.44 MPa at 1900 rpm were researched by experiments and simulation to broaden the load range of the present premixed charge compression ignition (PCCI) mode, and the following conclusions were gained
Summary
With increasing concerns about fossil fuel consumption, environmental protection, and stricter emission regulations, the production of engines urgently needs higher fuel conversion efficiency and lower emissions. Diesel engines are widely used in industry and traffic due to the advantages such like high heat efficiency and low fuel consumption. High nitrogen oxides (NOx ) and soot emissions have been the most prominent problem in diesel engines, so the newly developed diesel engine should have lower soot and NOx emissions when maintaining high thermal efficiency. Another challenge is the difficulty in simultaneously reducing the two types of emission, for which there is a trade-off [1,2]. Mueller et al [4]
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