Ducted fuel injection (DFI) has been shown to attenuate engine-out soot emissions from diesel engines. The concept is to inject fuel through a small tube within the combustion chamber to enable lower equivalence ratios at the autoignition zone, relative to conventional diesel combustion. Previous experiments have demonstrated that DFI enables significant soot attenuation relative to conventional diesel combustion for a small set of operating conditions at relatively low engine loads. This is the first study to compare DFI to conventional diesel combustion over a wide range of operating conditions and at higher loads (up to 8.5 bar gross indicated mean effective pressure) with a four-orifice fuel injector. This study compares DFI to conventional diesel combustion through sweeps of intake-oxygen mole fraction (XO2), injection duration, intake pressure, start of combustion (SOC) timing, fuel-injection pressure, and intake temperature. DFI is shown to curtail engine-out soot emissions at all tested conditions. Under certain conditions, DFI can attenuate engine-out soot by over a factor of 100. In addition to producing significantly lower engine-out soot emissions, DFI enables the engine to be operated at low-NOx conditions that are not feasible with conventional diesel combustion due to high soot emissions.
This project is focused on developing advanced combustion strategies for mixing-controlled compressionignition (i.e., diesel-cycle) engines that are synergistic with renewable and/or unconventional fuels in a manner that enhances domestic energy security, economic competitiveness, and environmental quality. During this reporting period, the focus was on ducted fuel injection (DFI), a technology that differs from conventional diesel combustion (CDC) in that it involves injecting fuel along the axis of one or more small cylindrical ducts within the combustion chamber. Each duct performs a function similar to the tube on a Bunsen burner, helping to premix the fuel with the charge-gas before ignition, creating a stable flame that forms little to no soot. The purpose of the work conducted during Fiscal Year (FY) 2019 was to begin determining the extent to which the use of oxygenated fuels, when combined with DFI and charge-gas dilution, can simultaneously lower the soot and nitrogen-oxides (N0x) emissions from mixing-controlled compression-ignition engines, and what the corresponding impacts on other regulated emissions and efficiency are likely to be.
Ducted fuel injection (DFI) is a technique to attenuate soot formation in compression ignition engines relative to conventional diesel combustion (CDC). The concept is to inject fuel through a small tube inside the combustion chamber to reduce equivalence ratios in the autoignition zone relative to CDC. DFI has been studied at loads as high as 8.5 bar gross indicated mean effective pressure (IMEPg) and as low as 2.5 bar IMEPg using a four-orifice fuel injector. Across previous studies, DFI has been shown to attenuate soot emissions, increase NOx emissions (at constant charge dilution), and slightly decrease fuel conversion efficiencies for most tested points. This study expands on the previous work by testing 1.1 bar IMEPg (low-load/idle) conditions and 10 bar IMEPg (higher-load) conditions with the same four-orifice fuel injector, as well as examining potential causes of the degradations in NOx emissions and fuel conversion efficiencies. DFI and CDC are directly compared at each operating point in the study. At the low-load condition, the intake charge dilution was swept to elucidate the soot and NOx performance of DFI. The low-load range is important because it is the target of impending, more-stringent emissions regulations, and DFI is shown to be a potentially effective approach for helping to meet these regulations. The results also indicate that DFI likely has slightly decreased fuel conversion efficiencies relative to CDC. The increase in NOx emissions with DFI is likely due to longer charge gas residence times at higher temperatures, which arise from shorter combustion durations and advanced combustion phasing relative to CDC.
Ducted fuel injection (DFI) has been proposed as a strategy to enhance the fuel/charge gas mixing within the combustion chamber of a direct-injection mixing-controlled compression ignition engine. The concept involves injecting each fuel spray through a small tube within the combustion chamber to facilitate the creation of a leaner mixture in the autoignition zone, relative to a conventional free-spray configuration (i.e., a fuel spray that is not surrounded by a duct). While previous experiments demonstrated that DFI lowers both soot incandescence and soot mass in a constant-volume combustion vessel with a single-component normal-alkane fuel (n-dodecane), this study provides the first evidence that the technology provides similar benefits in an engine application using a commercial diesel fuel containing ~30 wt% aromatics. The present study investigates the effects on engine-out emissions and efficiency with a two-orifice injector tip for charge gas mixtures containing 16 and 21 mol% oxygen. The result is that DFI is confirmed to be effective at curtailing engine-out soot emissions. It also breaks the tradeoff between emissions of soot and nitrogen oxides (NOx) by simultaneously attenuating soot and NOx with increasing dilution.
Ducted fuel injection is a strategy that can be used to enhance the fuel/charge-gas mixing within the combustion chamber of a direct-injection compression-ignition engine. The concept involves injecting the fuel through a small tube within the combustion chamber to make the most fuel-rich regions of the micture in the autoignition zone leaner relative to a conventional free-spray configuration (i.e., a fuel spray that is not surrounded by a duct). This study is a follow-on to initial proof-of-concept experiments that also were conducted in a constant-volume combustion vessel. While the initial natural luminosity imaging experiments demonstrated that ducted fuel injection lowers soot incandescence dramatically, this study adds a more quantitative diffuse back-illumination diagnostic to measure soot mass, as well as investigates the effects on performance of varying duct geometry (axial gap, length, diameter, and inlet and outlet shapes), ambient density, and charge-gas dilution level. The result is that ducted fuel injection is further proven to be effective at lowering soot by 35–100% across a wide range of operating conditions and geometries, and guidance is offered on geometric parameters that are most important for improving performance and facilitating packaging for engine applications.
The goal of this project is to create a modular optical section that can be inserted into an exhaust runner to measure soot mass being produced by combustion.
My oral presentation will focus on the progress made by me on mechanical design for the Exhaust Runner Soot Diagnostic (ERSD) for use on optical research diesel engines.
The Exhaust Runner Soot Diagnostic (ERSD) system is an in-line, time-resolved soot mass measurement system designed to allow rapid measurement of soot mass flux to detect and measure cyclic variability. The ERSD system design was generally split into two sections: conceptual mechanical design and measurement design—meaning the relevant calculations to demonstrate the feasibility of our planned measurement approach. For measurement design, the Beer-Lambert Law was the central focus for design justification. With measured values for the Filter Smoke Number (FSN) and a conversion to soot mass concentration, the required effective optical path length can be calculated for a desired light attenuation percentage. For mechanical design, the key constraints were space and modularity. The design must be placed into an existing mechanical setup with relative ease, as well as being modular enough to be implemented on other engines. The crux of the mechanical design was proper sealing and optical access, as both are crucial to the system's effectiveness. For proper sealing, extensive thermal expansion calculations were performed alongside O-ring design guides to produce the desired sealing and custom gland dimensions. For maximizing optical access, many iterations were modeled to provide full optical access while maintaining effective gas sealing.