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Abstract : The gasoline compression ignition (GCI) works on the principle of harnessing the benefits of light distillates in a compression ignition (CI) engine. Recent research has shown that along with air management and after-treatment systems; fuel systems also play a vital role in enabling GCI technology. The injector in the fuel injection system (FIS) is a key component driving the efficiency of the combustion phenomena. Subsequently, injection strategies, characteristics, and overall injection quality influence the combustion process and controls certain metrics like fuel consumption, pollutant emissions, and combustion noise. In this work, a one-dimensional (1-D) model of a heavy-duty diesel injector employed in Cummins ISX15 Engine, built in a commercially available computer software called Gamma Technologies (GT)-SUITE, was studied, and analyzed. This work focuses on developing a generalized methodology from previous work to adapt this injector with gasoline-like fuels by recalibrating the discharge coefficients using in-built GT-SUITE optimization techniques. Post recalibration, the 1-D model closely reproduces experimentally measured injection performance characteristics like rate of injection (ROI) profiles, injected quantities, hydraulic delays, and needle lift profiles for the heavy-duty, high-pressure diesel injector using gasoline-like fuels across engine operating points of interest, thereby enabling GCI. As the previous study has demonstrated the potential of injection rate shaping in the mitigation of oxides of nitrogen (NOx) emissions, this validated 1-D model was further used to investigate various injector geometries to produce custom injection rate shapes. Finally, an optimization methodology was developed to generate rate shape of interest to obtain a single set of the selected dimensional parameters across high-efficiency engine operating points using the in-built GT-SUITE optimization techniques. Furthermore, a full factorial design of experiments (DoE) using the candidate injector geometries, hydraulic components were simulated and post-processed to obtain an optimal rate shape, thereby acting as a validation tool for the optimal rate shape obtained using GT-Suite's optimization methods.
The combination of superior fuel economy and durability has made compression ignition direct injection diesel engines popular worldwide. However, these engines can emit large amounts of ozone-forming pollutants and particulates and so are being subjected to increasingly stringent regulations that require continual improvements in the combustion process. Further, improved engine power density is necessary at high load conditions, before the CIDI engine can be considered a contender in the next generation automotive engine technology. Understanding the physics and chemistry involved in diesel combustion, with its transient effects and the inhomogeneity of spray combustion is quite challenging. Great insight into the physics of the problem can be obtained when an in-cylinder computational analysis is used in conjunction with either an experimental program or through published experimental data. The main area to be investigated to obtain good combustion begins by defining the fuel injection process and the mean diameter of the fuel particle, injection pressure, drag coefficient, rate shaping, etc., correctly. This work presents a methodology to perform the task set out in the previous paragraph and uses experimental data obtained from available literature to construct a numerical model. A modified version of a multidimensional computer code called KIVA3V was used for the computations, with improved sub-models for mean droplet diameter, injection pressure and drop distortion and drag. The results achieved show good agreement with the published experimental data. It has been of special importance to model the spray distribution accurately, as the combustion process and the resulting pollutant emission formation is intimately tied to the in-cylinder fuel distribution. The present scheme has achieved excellent results in these aspects and will make an important contribution to the numerical simulation of the combustion process and pollutant emission formation in compression ignition direct injection engines.
Abstract : Recent developments in internal combustion engine technology have shown that gasoline compression ignition (GCI) combustion modes provide a viable pathway to meet future emission regulations. Lower octane middle distillate gasoline like fuels have also been formulated for GCI combustion applications and have shown similar benefits of improved fuel conversion efficiency and a reduction in particulate matter and nitrogen oxide emissions. As these gasoline like GCI fuels have not been well studied, characterization of their rate of injection (ROI) will be beneficial to supplement injector spray characterization measurements and the development of computational fluid dynamic simulations. A fuel collection method and data processing technique were defined to develop a measurement procedure for making rate of injection measurements with a Bosch type rate of injection (ROI) rig. The measurement procedure was developed to quantify the ROI for both heavy duty (HD) and light duty (LD) injector applications. The HD studies included ROI measurements using an Ultra-Low Sulfur Diesel (ULSD) and a research octane number (RON) 60 gasoline compression ignition (GCI) fuel. Rate of injection measurements for the HD fuels were obtained with an eight-hole high pressure common rail diesel Cummins XPI injector and electronic injection durations were successfully calibrated to provide a desired fuel quantity per injection. Single-hole ROI measurements were also made with a Cummins XPI injector designed to provide one-eighth of the flow of the multi-hole injector. These single-hole ROI measurements were used to supplement injector spray characterization data in an optically accessible combustion vessel. The LD studies characterized ROI measurements of a custom ten-hole Bosch HDEV5 gasoline direct injection (GDI) injector. The LD fuels studied were a premium octane CARB LEV III 10% ethanol (E10) certification gasoline and a RON 70 GCI fuel. These LD studies were conducted to compare the RON 70 GCI fuel's ROI characteristics to those of the premium octane CARB LEV III E10 certification gasoline. Average trends showed higher rates of injection and total mass per injection for the premium octane E10 cert gasoline and was attributed to the higher density of the fuel. Conclusions were also made that the higher viscosity of the E10 cert gasoline provided longer injector opening delays when compared to the RON 70 GCI fuel.
Downsizing of modern gasoline engines with direct injection is a key concept for achieving future CO22 emission targets. However, high power densities and optimum efficiency are limited by an uncontrolled autoignition of the unburned air-fuel mixture, the so-called spark knock phenomena. By a combination of three-dimensional Computational Fluid Dynamics (3D-CFD) and experiments incorporating optical diagnostics, this work presents an integral approach for predicting combustion and autoignition in Spark Ignition (SI) engines. The turbulent premixed combustion and flame front propagation in 3D-CFD is modeled with the G-equation combustion model, i.e. a laminar flamelet approach, in combination with the level set method. Autoignition in the unburned gas zone is modeled with the Shell model based on reduced chemical reactions using optimized reaction rate coefficients for different octane numbers (ON) as well as engine relevant pressures, temperatures and EGR rates. The basic functionality and sensitivities of improved sub-models, e.g. laminar flame speed, are proven in simplified test cases followed by adequate engine test cases. It is shown that the G-equation combustion model performs well even on unstructured grids with polyhedral cells and coarse grid resolution. The validation of the knock model with respect to temporal and spatial knock onset is done with fiber optical spark plug measurements and statistical evaluation of individual knocking cycles with a frequency based pressure analysis. The results show a good correlation with the Shell autoignition relevant species in the simulation. The combined model approach with G-equation and Shell autoignition in an active formulation enables a realistic representation of thin flame fronts and hence the thermodynamic conditions prior to knocking by taking into account the ignition chemistry in unburned gas, temperature fluctuations and self-acceleration effects due to pre-reactions. By the modeling approach and simulation methodology presented in this work the overall predictive capability for the virtual development of future knockproof SI engines is improved.
Direct Injection Systems: The Next Decade in Engine Technology explores potentials that have been recognized and successfully applied, including fuel direct injection, fully variable valve control, downsizing, operation within hybrid scenarios, and use of alternative fuels.