Effects of I-EGR and Pre-Injection on Performance of Gasoline Compression Ignition(GCI)at Low-Load Condition

Gasoline compression ignition(GCI)has been considered as a promising combustion concept to yield ultralow NOX and soot emissions while maintaining high thermal efficiency.However,how to improve the low-load performance becomes an urgent issue to be solved.In this paper,a GCI engine model was built to investigate the effects of internal EGR(i-EGR)and pre-injection on in-cylinder temperature,spatial concentration of mixture and OH radical,combustion and emission characteristics,and the control strategy for improving the combustion performance was further explored.The results showed an obvious expansion of the zone with an equivalence ratio between 0.8∼1.2 is realized by higher pre-injection ratios,and the s decreases with the increase of pre-injection ratio,but increases with the increase of i-EGR ratio.The high overlap among the equivalentmixture zone,the hightemperature zone,and the OH radical-rich zone can be achieved by higher i-EGR ratio coupled with higher preinjection ratio.By increasing the pre-injection ratio,the combustion efficiency increases first and then decreases,also achieves the peak value with a pre-injection ratio of 60%and is unaffected by i-EGR.The emissions of CO,HC,NOX,and soot can also be reduced to low levels by the combination of higher i-EGR ratios and a pre-injection ratio of 60%.

A statistic comparison of multi-element analysis of low atmospheric fine particles(PM_(2.5)) using different spectroscopy techniques

Over the past few decades,the metal elements(MEs)in atmospheric particles have aroused great attention.Some well-established techniques have been used to measure particlebound MEs.However,each method has its own advantages and disadvantages in terms of complexity,accuracy,and specific elements of interest.In this study,the performances of inductively coupled plasma-optical emission spectrometry(ICP-OES)and total reflection X-ray fluorescence spectroscopy(TXRF)were evaluated for quality control to analyze data accuracy and precision.The statistic methods(Deming regression and significance testing)were applied for intercomparison between ICP-OES and TXRF measurements for same lowloading PM_(2.5)samples in Weizhou Island.The results from the replicate analysis of standard filters(SRM 2783)and field filters samples indicated that 10 MEs(K,Ca,V,Cr,Mn,Fe,Ni,Cu,Zn,and Pb)showed good accuracies and precision for both techniques.The higher accuracy tended to the higher precision in the MEs analysis process.In addition,the interlab comparisons illustrated that V and Mn all had good agreements between ICP-OES and TXRF.The measurements of K,Cu and Zn were more reliable by TXRF analysis for low-loading PM_(2.5).ICP-OES was more accurate for the determinations for Ca,Cr,Ni and Pb,owing to the overlapping spectral lines and low sensitivity during TXRF analysis.The measurements of Fe,influenced by low-loading PM_(2.5),were not able to determine which instrument could obtain more reliable results.These conclusions could provide reference information to choose suitable instrument for the determination of MEs in low-loading PM_(2.5)samples.