Comparative Effect of Gasoline Formulations on Fuel Economy and Emissions of Modern GDI Engine

In this paper the effect of gasoline formulations on fuel economy and emissions were studied,aiming at exploring the optimized fuel formulation that can alleviate energy crisis and greenhouse effect to some extent.Five gasoline blends with same research octane number(RON)were designed and tested on a calibrated gasoline direct injection(GDI)engine under the mapped characteristic conditions.Test results illustrate that the optimized fuel formulation shows good superiority in fuel economy,and reduces carbon dioxide(CO2)emissions at low engine speeds with medium loads.The brake-specific fuel consumption(BSFC)decreased by a maximum value of 3.26%mainly because of the improvement of combustion velocity and the optimization of low heating value.The optimized fuel formulation simultaneously increases total hydrocarbon(THC)emissions.Nevertheless,it also markedly reduces CO2 emissions,reaching the maximum value of 2.34%.The research results can be applied practically by refineries to reduce the CO2 emissions and to alleviate the greenhouse effect.

The effects of EGR and ignition timing on emissions of GDI engine

The effects of EGR and ignition timing on engine emissions and combustion were studied through an experiment carried out on an air-guided GDI engine.The test results showed that the ignition timing significantly affected the GDI engine emissions,that the NOx emissions significantly reduced when the ignition timing was retarded,and that NOx emissions decreased with the EGR level increasement.A higher EGR rate could reduce CO emissions while the CO emissions were less affected by the ignition timing.The HC emissions decreased at a lower EGR rate.At 2500 r/min,an appropriate EGR rate could cut down CO emissions.The exhaust gas temperature could significantly decrease with improving the EGR rate,and the exhaust gas temperature at 2500 r/min was clearly higher than that at 1850 r/min.The nucleation mode particles increased clearly,the accumulation mode particle number decreased gradually with the increase of EGR rate,and the typical particle size of nucleation mode particle was in the range of 10–25 nm.

Suppression of super-knock in TC-GDI engine using two-stage injection in intake stroke(TSII)

Turbocharging and direct injection are main technologies used for energy-saving gasoline engines. But the biggest challenge is super-knock, whose mechanism is unclear and has no effective strategy to suppress this super-knock until now. The effects of injection strategies on super-knock were experimentally investigated in a turbocharged GDI engine. It was found that two-stage injections during intake stroke （TSII） can eliminate super-knock. Meanwhile, the fuel consumption, emissions and exhaust tem- perature can keep optimized level. By sweeping the start of the 1st injection （SOIl）, end of the 2nd injection （EOI2） and the split injection ratios （ROI2） using 5000 cycles evaluation test at low-speed high load operating point, the optimized injection strategy for the typical TC-GDI engine is TSII with SOIl at middle of intake stroke, EOI2 at end of intake stroke, and ROI2 of 0.3.

Ion Current Features of HCCI Combustion in a GDI Engine

Homogeneous charge compression ignition(HCCI)gasoline engines have the merit of good fuel economy and very low NOx emissions.The ion current signal in a gasoline direct injection-HCCI engine is the main focus of this paper.Experiments showed that the ion signal is significant correlated with the combustion status.Fuel spray and air-fuel mixture motions significant decrease the signal-to-noise ratio of the ion current signal.However,the current waveforms still vary regularly as the boundary conditions change,and their phases have significant linear relationships with the combustion phases.By combining the analysis with cylinder pressure data,the current can be used to effectively detect the combustion phase when the air fuel mixture is not lean.When the mixture gets leaner,the signal amplitude diminishes dramatically,and the linear correlation decreases substantially.The ratio of two-stage fuel injection has a strong effect on signal amplitude and combustion stability,and the linear relationship between the signal and combustion characteristics becomes insignificant as the pre-injection fuel amount decreases.A reaction kinetics analysis of the mechanism for the ion current signal in the HCCI engine explains the experimental observations.