# A Review of Early Injection Strategy in Premixed Combustion Engines
## 5 Blending Ratio
The lower cylinder temperature and more homogeneous charge resulted in decreased soot emissions. Higher HC and CO emissions observed with the increased gasoline ratio could be a combined result of increased crevice flow mass and less effective oxidization under the lower temperature. [PERSON] et al. [55] investigated the effects of fuel properties on soot reduction under early injection conditions in a diesel engine. Results showed that as the gasoline ratio was increased from 0% to 70%, soot emissions were reduced dramatically. On the one hand, with an increased gasoline ratio, ignition delay was prolonged and fuel-air had better mixing. On the other hand, the increased gasoline proportion caused higher fuel vaporization, which shortened the spray penetration and reduced the fuel wall-wetting. In addition, the effect of n-butanol was also studied. With increasing n-butanol ratio, ignition delay increased and soot emissions decreased obviously. This was because the oxygen atoms in n-butanol could enter over-rich regions and consume soot precursors, resulting in reduced soot emissions. [PERSON] et al. [82] also experimentally investigated the influence of the diesel fuel n-butanol blending ratio on the performance and emissions of a two-stage injection HD diesel engine fueled by n-butanol/diesel. Diesel fuels with different amounts of n-butanol (0%, 5%, 10%, and 15%) were used. Results showed that oxygenated fuel could get much lower soot and CO emissions compared to the base diesel. A higher n-butanol fraction in the blend could get lower soot and CO emissions, since the oxygenated addition was effective in fuel-rich regions. The density and cetane number of n-butanol are lower than those of diesel, therefore further increasing n-butanol in a blend will prolong injection duration and ignition delay. More fuel will burn during the expand stroke with relatively lower combustion efficiency, which will cause increased BSFC. [PERSON] et al. [101] reported the effects of 10%, 20%, and 50% Karanja biodiesel blends on injection rate, atomization, engine performance, emissions, and combustion characteristics of a common rail direct-injection (CRDI)-type fuel injection system evaluated in a single cylinder. The results showed that as the blend ratio increased, BSFC increased obviously. As for emissions, NOx decreased, but HC and CO increased because the higher blend ratio caused inferior mixing of fuel with air. [PERSON] et al. [87] compared the effects on performance and emissions of an HCCI engine with four blend ratios of fuel (E10, E20, M10, and M20). The results showed that with increased ethanol content, Pmax decreased; meanwhile, higher methanol content meant lower maximum pressure (Pmax). In addition, the oxygen in the blended fuel and in-cylinder temperature affected by the physical properties of the additive had a direct influence on NOx and CO emissions. [PERSON] et al. [102] studied the performance and combustion characteristics of a compression ignition engine running on (diesel biodiesel ethanol) DBEblends. The engine was fueled with B15E5, B15E10, and B15E15 (B, biodiesel; E, ethanol). At the same speed of torque and injection timing, results showed that BSFC increased with increased ethanol content due to the lower heating value. Table 8 shows a summary of the variation of performance and emissions of HCCI and PCCI engines after increasing the blending ratio of alternative fuels. In general, for oxygenated fuel, the high heat of evaporation and lower heating value lead to reduced combustion temperature, which is beneficial for reducing NOx emissions, but is not good for the oxidation of HC, CO, and soot emissions. However, the high oxygen content of oxygenated fuel helps to consume soot precursors and HC and CO emissions in the over-rich region. Besides, the liquid penetration of the spray becomes longer with increased oxygenated because of the change of the physical properties of injected fuel, resulting in a more serious wall-wetting phenomenon.