Diagnostics and characterization of direct injection of liquified petroleum gas for development of spray models at engine-like conditions
Date
2023
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Abstract
Research within the realm of internal combustion (IC) engines is concentrated on enhancing fuel efficiency and curbing tailpipe emissions, particularly CO2 and regulated pollutants. Promising solutions encompass the utilization of direct injection (DI) and alternative fuels, with liquefied petroleum gas (LPG) standing out as a notable candidate. LPG presents a pragmatic and economical option for fueling the heavy-duty transportation sector in the United States. However, widespread adoption hinges on achieving energy conversion efficiencies in LPG engines comparable to those in diesel engine platforms. The overarching goal of this research is to address fundamental limitations to achieving or surpassing near-diesel efficiencies in heavy-duty on-road liquefied petroleum gas engines. Owing to substantial differences in physical properties compared to traditional fuels, an enhanced understanding and modeling of LPG sprays become imperative. This work conducts an experimental and numerical analysis of direct-injected propane and iso-octane, serving as surrogates for LPG and gasoline, respectively, under diverse engine-like conditions. The overall objective is to establish a baseline for the fuel delivery system required in future high-efficiency DI-LPG heavy-duty engines. Propane, emulating LPG, undergoes injection across various engine-like conditions, encompassing early and late injections, as well as boosted engines, using a range of direct injectors available in both research and commercial domains. Optical diagnostics, including high-speed schlieren and planar Mie scattering imaging, were performed to study the spray penetration, liquid and vapor phase regions, and mixing of propane and to characterize bulk and the plume-specific spray behavior of propane. The study also investigates the influence of injector geometry on spray performance. Iso-octane was used as a surrogate for gasoline, and propane was used to compare LPG's behavior with more conventional DI fuel. The experimental results and high-fidelity internal nozzle-flow simulations were then used to define best practices in computational fluid dynamics (CFD) Lagrangian spray models. Optical imaging revealed that, unlike iso-octane, propane's spray propagation was fed by its flash boiling, spray collapse, and a high degree of vaporization, resulting in a direct proportionality of propane's penetration length to temperature. These unique attributes categorize propane as an unconventional spray, necessitating corrections to injection and breakup models to replicate under-expanded jet dynamics and emulate flash boiling-driven spray development across various research and commercial injectors.
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Rights Access
Subject
direct injection
liquified petroleum gas
spray model
engine-relevant conditions
diesel-like efficiency
spray diagnostics