Investigations on the Spray-Atomization of various Fuels for an outwardly opening Piezo Injector for the Application to a Pilot Injection Passenger Car Gas Engine
Pilot injection gas engines are commonly used as large stationary engines. Often, the combustion is implemented as a dual-fuel strategy, which allows both mixed and diesel-only operation, based on a diesel engine architecture. The current research project focuses on the application of pilot injection in an engine based on gasoline components of the passenger car segment, which are more cost-effective than diesel components. The investigated strategy does not aim for a diesel-only combustion, hence only small liquid quantities are used for the main purpose of providing a strong, reliable ignition source for the natural gas charge. This approach is mainly driven to provide a reliable alternative to the high spark ignition energies required for high cylinder charge densities.
When using such small liquid quantities, a standard common-rail diesel nozzle will apparently not be ideal regarding some general specifications. Due to this fact, an outwardly opening piezo injector is intended to be used due to its high performance in several aspects. An issue, which is almost unknown in literature, is the atomization behavior for fuel types differing significantly from the viscosity properties of regular gasoline fuel.
The aim of this publication is to clarify, whether the outwardly opening piezo injector can produce an atomization quality, which is sufficient to be used as a pilot injection ignition source for natural gas engines. The experimental results were obtained by means of a combined methodology using both Mie-scattering and PDA (Phase Doppler Anemometry) in a constant volume chamber. The injected masses showed a difference of up to 30% for the examined fuels, whereas liquid penetrations displayed a smaller difference. The Sauter Mean Diameters (SMD) for diesel-like fuels were 5?10μm larger compared to operation on gasoline-like fuels. Additionally, the needle motion for given actuation parameters was studied using a laser vibrometer. Influences of rail pressure, injector temperature, actuation time and reproducibility were investigated, showing that the injector has great reproducibility, but on the other hand requires a complex understanding of the actuation strategy in engine operation.