Influence of Ethanol Blends on Low Speed Pre-Ignition in Turbocharged, Direct-Injection Gasoline Engines 2017-01-0687

Modern combustion engines must meet increasingly higher requirements concerning emission standards, fuel economy, performance characteristics and comfort. Especially fuel consumption and the related CO₂ emissions were moved into public focus within the last years. One possibility to meet those requirements is downsizing. Engine downsizing is intended to achieve a reduction of fuel consumption through measures that allow reducing displacement while simultaneously keeping or increasing power and torque output. However, to reach that goal, downsized engines need high brake mean effective pressure levels which are well in excess of 20bar. When targeting these high output levels at low engine speeds, undesired combustion events with high cylinder peak pressures can occur that can severely damage the engine. These phenomena, typically called low speed pre-ignition (LSPI), set currently an undesired limit to downsizing.

This study analyzes the influence of ethanol fuel content on low speed pre-ignition events in a direct-injection turbo charged gasoline engine with a homogeneous (λ = 1) common rail high pressure injection system, side mounted multi-hole injectors and dual variable valve timing. All experiments were conducted on a steady state engine test bench with intake air, coolant, oil and fuel conditioning to be able to separate fuel effects from boundary condition influences. In addition, the engine was equipped with a prototype engine controller that allows to negate the influence of control algorithms on combustion. Four ethanol fuels containing different levels of ethanol were blended using the same base fuel and denatured ethanol. The investigated blends included E10, E20, E30 and E50 fuels. Subsequently, test runs were performed to understand the impact of different ethanol blends on occurrence, number and pressure characteristics of LSPI.