4.2.2. Use of E85-diesel in a light-duty multi-cylinder engine
The effect of alternative fuels, i.e., E85 on load expansion and Federal Test Procedure (FTP) modal point emissions indices under RCCI operation has been investigated by Curran et al. [93]. The GM 1.9L four-cylinder engine shown in Fig. 2 was modified to allow port fuel injection and operated with E85. The effect of E85 on the Ad-hoc FTP modal points was explored, along with the effect of load expansion throughout the LD diesel engine's speed range. Previous results [90] with gasoline-diesel dual-fuel operation showed that with the stock hardware, the 2600 rev/min, 8.8 bar BMEP modal point was not obtainable due to an excessive cylinder pressure rise rate and unstable combustion both with and without
EGR. In this experiment the performance and emissions of RCCI operation with E85 and diesel was explored and compared against CDC and RCCI operation with gasoline and diesel. The use of renewable fuels such as E85 not only has the potential for expanding the operating load of RCCI, but also is effective for decreasing petroleum energy use through a combination of direct petroleum displacement and increased efficiency, as well as a reduction in life-cycle emissions.
Formaldehyde emissions were not examined by Curran et al. [93], but a previous study [94] revealed increased HCHO production compared to CDC and PCCI with RCCI operation. It was concluded that a diesel oxidation catalyst could be effective in controlling the tailpipe emissions. RCCI operation with E85 was achieved through early DI (single or double pulse) of diesel fuel (between 30 and 70o bTDC) and port fueling of E85 onto a closed intake valve. The fuel
rail pressure was decreased to 500 bar as the diesel fuel start of injection was advanced to avoid spray impingement on the cylinder walls. For RCCI operation with the stock piston geometry and stock DI diesel injectors, it was found that increased swirl intensity is needed to create a well-mixed cylinder charge [93] for the highest BTE and lowest possible emissions, and the mass ratio of premixed fuel to direct injected fuel varied depending on engine speed and load. As the load increased, the premixed fuel ratio was required to
increase and SOI was advanced toward 60o bTDC for both gasoline
and E85, as shown in Fig. 69.