From Idle to 7.5 Bar IMEPg – Using Fuel Stratification to Control LTGC with Next-Cycle Capability

Abstract

<div class="section abstract"><div class="htmlview paragraph">Low-temperature gasoline combustion (LTGC) engines can provide high efficiencies with very low NOx and soot emissions, but rapid control of the combustion timing remains a challenge. Partial Fuel Stratification (PFS) was demonstrated to be an effective approach to control combustion in LTGC engines. PFS is produced by a double-direct injection (DI) strategy with most of the fuel injected early in the cycle and the remainder of the fuel supplied by a second injection at a variable time during the compression stroke to vary the amount of stratification. Adjusting the stratification changes the combustion phasing, and this can be done on cycle-to-cycle basis by adjusting the injection timing.</div><div class="htmlview paragraph">In this paper, the ability of PFS to control the combustion during wide engine load sweeps is assessed for regular gasoline and gasoline doped with 2-ethylhexyl nitrate (EHN). For PFS, the load control range is limited by combustion instability and poor combustion efficiency at low loads. However, late single-DI stratification was demonstrated to allow robust control at low loads with good combustion efficiency by concentrating the fuel in the middle of the chamber, avoiding overly lean regions. Stratification is more effective with EHN-doped gasoline than with straight gasoline because EHN enhances the reactivity and φ–sensitivity of the fuel. Thus, lower intake temperatures and less stratification are required when working with EHN-doped gasoline. The combination of PFS at higher loads and late single-DI at lower loads allows load control ranges from 1.0 to 4.8 bar IMEPg using regular gasoline and from idle to 5.6 bar IMEPg using EHN-doped gasoline at naturally aspirated conditions. Combustion control using only stratification is also demonstrated at boosted conditions, allowing the IMEPg to be varied from idle to 7.5 bar by combining two boost levels (1.3 and 1.0 bar intake) and two EHN flow levels.</div></div>