MAP | CALMAIL |
Combustion Modeling Lab at UC Berkeley

Current Research

Partial Fuel Stratification for HCCI Engines


Ben Wolk

In conjuction with the Combustion Research Facility


Introduction

In order to limit carbon dioxide and pollutant emissions from internal combustion (IC) engines, next-generation low-temperature compression ignition (CI) combustion modes that reduce exhaust emissions and improve thermal efficiency are currently being explored. For HCCI at high loads, extremely rapid combustion can occur leading to knock (pressure oscillations) and, ultimately, engine damage. HCCI must use lean fuel-air mixtures or high levels of exhaust gas recirculation (EGR) to lower the heat release rate such that the maximum pressure rise rate is acceptable. Although homogeneous fuel mixtures are targeted in HCCI combustion, thermal stratification has been shown to play an important role in dictating the heat release and maximum pressure rise rates. Fuel stratification has also been shown to influence the heat release and maximum pressure rise rates.

Stratified HCCI, or SCCI, aims to reduce the maximum pressure rise rate by using partial fuel stratification to prolong combustion and enable engine operation at high load conditions. Partial fuel stratification is accomplished by mixing the majority of the fuel with intake air and direct-injecting (DI) the rest during the compression stroke. The goal of preparing a stratified mixture is to promote sequential auto-ignition that reduces the maximum pressure rise rate. The fuel auto-ignition chemistry is critical in SCCI and the behavior of partial fuel stratification depends on how the auto-ignition characteristics of the fuel (or fuel-blend) change with equivalence ratio and if the fuel exhibits single- or multi-stage ignition.

Related papers

Computational study of partial fuel stratification using gasoline surrogate reduced mechanism

Computational study of the pressure dependence of sequential auto-ignition for partial fuel stratification with gasoline