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A study of partially premixed combustion (PPC) with non-oxygenated 91 pump octane number1 (PON) commercially available gasoline was performed using a heavy-duty (HD) compression-ignition (CI) 2.44 l Caterpillar 3401E single-cylinder oil test engine (SCOTE). The experimental conditions selected were a net indicated mean effective pressure (IMEP) of 11.5 bar, an engine speed of 1300 rev/min, an intake temperature of 40°C with intake and exhaust pressures of 200 and 207 kPa, respectively. The baseline case for all studies presented had 0% exhaust gas recirculation (EGR), used a dual injection strategy a -137 deg ATDC pilot SOI and a -6 deg ATDC main start-of-injection (SOI) timing with a 30/70% pilot/main fuel split for a total of 5.3 kg/h fueling (equating to approximately 50% load). Combustion and emissions characteristics were explored relative to the baseline case by sweeping main and pilot SOI timings, injection split fuel percentage, intake pressure, load and EGR levels.

Neural networks are useful tools for optimization studies since they are very fast, so that while capturing the accuracy of multi-dimensional CFD calculations or experimental data, they can be run numerous times as required by many optimization techniques. This paper describes how a set of neural networks trained on a multi-dimensional CFD code to predict pressure, temperature, heat flux, torque and emissions, have been used by a genetic algorithm in combination with a hill-climbing type algorithm to optimize operating parameters of a diesel engine over the entire speed-torque map of the engine. The optimized parameters are mass of fuel injected per cycle, shape of the injection profile for dual split injection, start of injection, EGR level and boost pressure. These have been optimized for minimum emissions. Another set of neural networks have been trained to predict the optimized parameters, based on the speed-torque point of the engine.

This research explored methods to reduce regulated emissions in a small-bore, direct-injection diesel engine. Swirl was used to influence mixing of the spray plumes, and alternative fuels were used to study the effects of oxygenated and water microemulsion diesel fuels on emissions. Air/fuel mixing enhancement was achieved in the running engine by blocking off a percentage of one of the two intake ports. The swirl was characterized at steady-state conditions with a flowbench and swirl meter. Swirl ratios of 1.85, 2.70, and 3.29 were studied in the engine tests at full load with engine speeds of 1303, 1757, and 1906 rev/min. Increased swirl was shown to have negative effects on emissions due to plume-to-plume interactions. Blends of No. 2 diesel and biodiesel were used to investigate the presence of oxygen in the fuel and its effects on regulated emissions. Pure No. 2 diesel fuel, a 15% and a 30% biodiesel blend (by weight) were used.

Micro-machined planar orifice nozzles have been developed and used with commercially produced diesel injection systems. Such a system may have the capability to improve the spray characteristics in DI diesel engines. The availability of a MEMS (Micro-Electro-Mechanical-Systems) processing sequence supported the construction of micro-planar orifice nozzles, and micro-systems technology was also employed in our macro-instrumentation. To demonstrate this process, fourteen MEMS nozzles were fabricated with deep X-ray lithography and electroplating technology. The circular orifice diameters were varied from 40 to 260 microns and the number of orifices varied from one to 169. Three plates with non-circular orifices were also fabricated to examine the effect of orifice shape on spray characteristics. These nozzles were then attached to commercial injectors and the associated injection systems were used for the spray experiments.

A study of the combined use of split injections, EGR, and flexible boosting was conducted. Statistical optimization of the engine operating parameters was accomplished using a new response surface method. The objective of the study was to demonstrate the emissions and fuel consumption capabilities of a state-of-the-art heavy -duty diesel engine when using split injections, EGR, and flexible boosting over a wide range of engine operating conditions. Previous studies have indicated that multiple injections with EGR can provide substantial simultaneous reductions in emissions of particulate and NOx from heavy-duty diesel engines, but careful optimization of the operating parameters is necessary in order to receive the full benefit of these combustion control techniques. Similarly, boost has been shown to be an important parameter to optimize. During the experiments, an instrumented single-cylinder heavy -duty diesel engine was used.

The present study investigated HCCI combustion in a heavy-duty diesel engine both experimentally and numerically. The engine was equipped with a hollow-cone pressure-swirl injector using gasoline direct injection. Characteristics of HCCI combustion were obtained by very early injection with a heated intake charge. Experimental results showed an increase in NOx emission and a decrease in UHC as the injection timing was retarded. It was also found that optimization can be achieved by controlling the intake temperature together with the start-of-injection timing. The experiments were modeled by using an engine CFD code with detailed chemistry. The CHEMKIN code was implemented into KIVA-3V such that the chemistry and flow solutions were coupled. The model predicted ignition timing, cylinder pressure, and heat release rates reasonably well. The NOx emissions were found to increase as the injection timing was retarded, in agreement with experimental results.

Vapor concentration measurements were performed for two unit injectors typically found in small- and medium-bore applications under evaporating conditions similar to those experienced in Diesel engines. Ambient gas temperatures of 800 and 1000 K and an ambient density of 15 kg/m3 were investigated using a constant volume combustion-type spray chamber. The exciplex laserinduced fluorescence technique with TMPD/naphthalene doped into the fuel was used to quantitatively determine the vapor-phase concentration and liquid-phase extent. The vapor-phase concentration was quantified using a previously developed method that includes corrections for the temperature dependence of the TMPD fluorescence, laser sheet absorption, and the laser sheet intensity profile. The effect of increasing ambient temperature (1000 vs. 800 K) was significant on intact liquid length, and on the spray-spreading angle in the early portion of the injection period.

The Diesel engine is a commercially attractive powerplant, however it is noted to have significant specific output of harmful emissions under some operating conditions. One possible solution for reduction of the harmful emissions from the Diesel engine is greater control over the fuel injection event. To gain further understanding of liquid phase Diesel fuel injection spray characteristics, a 2.44 liter displacement, 4 stroke engine was modified for optical access and fitted with a Caterpillar Hydraulic Electronic Unit Injection (HEUI) system. The data collection system consisted of a high repetition rate diode pumped Nd:YAG laser frequency doubled to 532 nm for visible illumination and a Kodak High Speed Motion Analyzer for recording fuel spray images. The engine was motored under various inlet conditions to create an engine combustion chamber environment typical of those found in commercial engines of similar per cylinder displacement class.

An experimental study was performed to investigate the effect of fuel composition on combustion, gaseous emissions, and detailed chemical composition and size distributions of diesel particulate matter (PM) in a modern heavy-duty diesel engine with the use of the enhanced full-dilution tunnel system of the Engine Research Center (ERC) of the UW-Madison. Detailed description of this system can be found in our previous reports [1,2]. The experiments were carried out on a single-cylinder 2.3-liter D.I. diesel engine equipped with an electronically controlled unit injection system. The operating conditions of the engine followed the California Air Resources Board (CARB) 8-mode test cycle. The fuels used in the current study include baseline No. 2 diesel (Fuel A: sulfur content = 352 ppm), ultra low sulfur diesel (Fuel B: sulfur content = 14 ppm), and Fisher-Tropsch (F-T) diesel (sulfur content = 0 ppm).

An experimental study was carried out to investigate the effects of fuel injection timing on detailed chemical composition and size distributions of diesel particulate matter (PM) and regulated gaseous emissions in a modern heavy-duty D.I. diesel engine. These measurements were made for two different diesel fuels: No. 2 diesel (Fuel A) and ultra low sulfur diesel (Fuel B). A single-cylinder 2.3-liter D.I. diesel engine equipped with an electronically controlled unit injection system was used in the experiments. PM measurements were made with an enhanced full-dilution tunnel system at the Engine Research Center (ERC) of the University of Wisconsin-Madison (UW-Madison) [1, 2]. The engine was run under 2 selected modes (25% and 75% loads at 1200 rpm) of the California Air Resources Board (CARB) 8-mode test cycle.

Diesel engine in-cylinder combustion processes have been studied using computational models with particular attention to spray development, vaporization, fuel/air mixture formation and combustion. A thermodynamic zero-dimensional cycle analysis program was used to determine initial conditions for the multidimensional calculations. A modified version of the time-dependent, three-dimensional computational fluid dynamics code KIVA-II was used for the computations, with a detailed treatment for the spray calculations and a simplified model for combustion. The calculations were used to obtain an understanding of the potential predictive capabilities of the models. It was found that there is a strong sensitivity of the results to numerical grid resolution. With proper grid resolution, the calculations were found to reproduce experimental data for non- vaporizing and vaporizing sprays. However, for vaporizing sprays with combustion, extremely fine grids are needed.

A single cylinder, Cummins NH, direct-injection, diesel engine has been operated in order to evaluate the effects of aromatic content and aromatic structure on diesel engine particulates. Results from three fuels are shown. The first fuel, a low sulfur Chevron diesel fuel was used as a base fuel for comparison. The other fuels consisted of the base fuel and 10% by volume of 1-2-3-4 tetrahydronaphthalene (tetralin) a single-ring aromatic and naphthalene, a double-ring aromatic. The fuels were chosen to vary aromatic content and structure while minimizing differences in boiling points and cetane number. Measurements included exhaust particulates using a mini-dilution tunnel, exhaust emissions including THC, CO2, NO/NOx, O2, injection timing, two-color radiation, soluble organic fraction, and cylinder pressure. Particulate measurements were found to be sensitive to temperature and flow conditions in the mini-dilution tunnel and exhaust system.

In this work, linear, non-linear and a generalized renormalization group (RNG) two-equation RANS turbulence models of the k-epsilon form were compared for the prediction of turbulent compressible flows in diesel engines. The object-oriented, multidimensional parallel code FRESCO, developed at the University of Wisconsin, was used to test the alternative models versus the standard k-epsilon model. Test cases featured the academic backward facing step and the impinging gas jet in a quiescent chamber. Diesel engine flows featured high-pressure spray injection in a constant volume vessel from the Engine Combustion Network (ECN), as well as intake flows in a high-swirl diesel engine. For the engine intake flows, a model of the Sandia National Laboratories 1.9L light-duty single cylinder optical engine was used.

In a recent study, quantitative measurements were presented of in-cylinder spatial distributions of mixture equivalence ratio in a single-cylinder light-duty optical diesel engine, operated with a non-reactive mixture at conditions similar to an early injection low-temperature combustion mode. In the experiments a planar laser-induced fluorescence (PLIF) methodology was used to obtain local mixture equivalence ratio values based on a diesel fuel surrogate (75% n-heptane, 25% iso-octane), with a small fraction of toluene as fluorescing tracer (0.5% by mass). Significant changes in the mixture's structure and composition at the walls were observed due to increased charge motion at high swirl and injection pressure levels. This suggested a non-negligible impact on wall heat transfer and, ultimately, on efficiency and engine-out emissions.

Using modified versions of the KIVA-II and KIVA-3 CFD codes, intake, compression, and combustion of a Caterpillar diesel engine was modeled. Seven variations on intake and two injection schemes were explored so that a detailed understanding of the effects of intake on various flow properties and their subsequent influence on combustion and emissions could be obtained. The results revealed that, in many cases, one of three factors: swirl ratio, temperature, and turbulence, was dominant in describing a combustion or emission behavior. In addition, stratification of fuel and oxygen was found to be a result of high swirl ratios. This had a profound impact on combustion and emissions, especially for split injection cases.

Intake port and cylinder flow have been modeled for a dual intake valve diesel engine. A block structured grid was used to represent the complex geometry of the intake port, valves, and cylinder. The calculations were made using a pre-release version of the KIVA-3 code developed at Los Alamos National Laboratories. Both steady flow-bench and unsteady intake calculations were made. In the flow bench configuration, the valves were stationary in a fully open position and pressure boundary conditions were implemented at the domain inlet and outlet. Detailed structure of the in-cylinder flow field set up by the intake flow was studied. Three dimensional particle trace streamlines reveal a complex flow structure that is not readily described by global parameters such as swirl or tumble. Streamlines constrained to lie in planes normal to the cylinder axis show dual vortical structures, which originated at the valves, merging into a single structure downstream.

The three-dimensional computer code, KIVA, is being modified to include state-of-the-art submodels for diesel engine flow and combustion. Improved and/or new submodels which have already been implemented are: wall heat transfer with unsteadiness and compressibility, laminar-turbulent characteristic time combustion with unburned HC and Zeldo'vich NOx, and spray/wall impingement with rebounding and sliding drops. Progress on the implementation of improved spray drop drag and drop breakup models, the formulation and testing of a multistep kinetics ignition model and preliminary soot modeling results are described. In addition, the use of a block structured version of KIVA to model the intake flow process is described. A grid generation scheme has been developed for modeling realistic (complex) engine geometries, and initial computations have been made of intake flow in the manifold and combustion chamber of a two-intake-valve engine.

This paper investigates the dynamic errors between the commonly used two-lump mass connecting rod model and the actual connecting rod model for the internal combustion engine. Because of the errors between the actual rod inertia and this simplified two-lump mass model, incorrect engine dynamics and internal forces are often predicted. In this paper, the magnitudes of force differences related to errors of connecting rod inertia are presented for various engines at different engine operating speeds. A method to predict the maximum side force and its maximum deviation is presented. And the technique to minimize variability in connecting rod mass and moment of inertia, as well as minimizing errors in the lumped mass model commonly used in industry are also introduced to avoid incorrect engine dynamics and internal forces.

Intake valve flow patterns have been measured quantitatively using particle image velocimetry (PIV) for a commercial 4-valve diesel cylinder head and valve system. The measurements have been made for low (600 engine RPM) and higher (1000 engine RPM) speeds, and at several planes in the valve curtain area. The measurements involve double exposure photography of laser light scattered by seed particles (≅1 μm) from a laser light sheet (≅ 0.5 mm by 50 mm) through an imaging system onto silver halide film. Subsequent processing produces the local particle displacement between the two exposures. Combined with the known time interval between exposures, the displacement information can produce velocity vectors at many locations in the field of view. The results of the experiments are shown as vector plots for each operating condition. In the plane of the illuminating laser sheet, velocity vectors representing local gas velocity are produced.

A new technique which is based on optoacoustic phenomena has been developed for measuring in-cylinder gas temperature and turbulent diffusivity. In the experiments, a high energy Nd:YAG pulsed laser beam was focused to cause local ionization of air at a point in the combustion chamber. This initiates a shock wave and creates a hot spot. The local temperature and turbulent diffusivity are determined by monitoring the shock propagation and the hot spot growth, respectively, with a schlieren photography system. In order to assess the validity and accuracy of the measurements, the technique was also applied to a turbulent jet. The temperature measurements were found to be accurate to within 3%. Results from the turbulent jet measurements also showed that the growth rate of the hot spot diameter can be used to estimate the turbulent diffusivity. In-cylinder gas temperature measurements were made in a motored single cylinder Caterpillar diesel engine, modified for optical access.