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The effect of low level ethanol fuel on the power and emissions characteristics was studied in a small, mass produced, carbureted, spark-ignited, Briggs and Stratton Vanguard 19L2 engine. Ethanol has been shown to be an attractive renewable fuel by the automotive industry; having anti-knock properties, potential power benefits, and emissions reduction benefits. With increasing availability and the possible mandates of higher ethanol content in pump gasoline, there is interest in exploring the effect of using higher content ethanol fuels in the small utility engine market. The fuels in this study were prepared by gravimetrically mixing 98.7% ethanol with a balance of 87 octane no-ethanol gasoline in approximately 5% increments from pure gasoline to 25% ethanol. Alcor Petrolab performed fuel analysis on the blended fuels and determined the actual volumetric ethanol content was within 2%.

Due to concerns regarding pollutant and CO2 emissions, advanced combustion modes that can simultaneously reduce exhaust emissions and improve thermal efficiency have been widely investigated. The main characteristic of the new combustion strategies, such as HCCI and LTC, is that the formation of a homogenous mixture or a controllable stratified mixture is required prior to ignition. The major issue with these approaches is the lack of a direct method for the control of ignition timing and combustion rate, which can be only indirectly controlled using high EGR rates and/or lean mixtures. Homogeneous Charge Progressive Combustion (HCPC) is based on the split-cycle principle. Intake and compression phases are performed in a reciprocating external compressor, which drives the air into the combustor cylinder during the combustion process, through a transfer duct. A transfer valve is positioned between the compressor cylinder and the transfer duct.

A fundamentally based quasi-dimensional NOx emission model for spark ignition direct injection (SIDI) gasoline engines was developed. The NOx model consists of a chemical mechanism and three sub-models. The classical extended Zeldovich mechanism and N₂O pathway for NOx formation mechanism were employed as the chemical mechanism in the model. A characteristic time model for the radical species H, O and OH was incorporated to account for non-equilibrium of radical species during combustion. A model of homogeneity which correlates fundamental dimensionless numbers and mixing time was developed to model the air-fuel mixing and inhomogeneity of the charge. Since temperature has a dominant effect on NOx emission, a flame temperature correlation was developed to model the flame temperature during the combustion for NOx calculation. Measured NOx emission data from a single-cylinder SIDI research engine at different operating conditions was used to validate the NOx model.

Many recent studies have shown that the Reactivity Controlled Compression Ignition (RCCI) combustion strategy can achieve high efficiency with low emissions. However, it has also been revealed that RCCI combustion is difficult at high loads due to its premixed nature. To operate at moderate to high loads with gasoline/diesel dual fuel, high amounts of EGR or an ultra low compression ratio have shown to be required. Considering that both of these approaches inherently lower thermodynamic efficiency, in this study natural gas was utilized as a replacement for gasoline as the low-reactivity fuel. Due to the lower reactivity (i.e., higher octane number) of natural gas compared to gasoline, it was hypothesized to be a better fuel for RCCI combustion, in which a large reactivity gradient between the two fuels is beneficial in controlling the maximum pressure rise rate.

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.

The purpose of this research is to develop a prediction technique that can be used in the development of port fuel-injection (hereinafter called PFI) gasoline engines, especially for general purpose small utility engines. Utility engines have two contradictory desirable aspects: compactness and high-power at wide open throttle. Therefore, applying the port fuel injector to utility engines presents a unique intractableness that is different from application to automobiles or motorcycles. At the condition of wide open throttle, a large amount of fuel is required to output high power, and injected fuel is deposited as a wall film on the intake port wall. Despite the fuel rich condition, emissions are required to be kept under a certain level. Thus, it is significant to understand the wall film phenomenon and control film thickness in the intake ports.

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.

A direct injection-gasoline (DI-G) system was applied to a heavy-duty diesel-type engine to study the effects of charge stratification on the performance of premixed compression ignited combustion. The effects of the fuel injection parameters on combustion phasing were of primary interest. The simultaneous effects of the fuel stratification on Unburned Hydrocarbon (UHC), Oxides of Nitrogen (NOx), Carbon Monoxide (CO), and smoke emissions were also measured. Engine tests were conducted with altered injection parameters covering the entire load range of normally aspirated Homogeneous Charge Compression Ignited (HCCI) combustion. Combustion phasing tests were also conducted at several engine speeds to evaluate its effects on a fuel stratification strategy.

An investigation of several diesel injector nozzles that produced different engine emissions performance was performed. The nozzle styles used were two VCO type nozzles that were manufactured using two different techniques, and two mini-sac nozzles that provided comparison. Fired experiments were conducted on a Detroit Diesel Series 50 engine. Optical access was obtained by substituting a sapphire window for one exhaust valve. Under high speed, high load, retarded injection timing conditions, it was discovered that each nozzle produced different specific soot and NOx emissions. High-speed film images were obtained. It was discovered that the temperature and KL factor results from the 2-color optical pyrometry showed significant differences between the nozzles. The authors propose the possibility that differences in air entrainment, caused by potential differences in CD due to surface finish, may contribute to the variance in emissions performance.

Oxygen enhancement in a direct injection (DI) diesel engine was studied to investigate the potential for particulate matter and NOx emissions control. The local oxygen concentration within the fuel plume was modified by oxygen enrichment of the intake air and by oxygenating the base fuel with 20% methyl t-butyl ether (MTBE). The study collected overall engine performance and engine-out emissions data as well as in-cylinder two-color measurements at 25% and 75% loads over a range of injection timings. The study found oxygen enhancement, whether it be from intake air enrichment or via oxygenated fuels, reduces particulate matter, the effectiveness depending on the local concentration of oxygen in the fuel plume. Since NOx emissions depend strongly on the temperature and oxygen concentration throughout the bulk cylinder gas, the global thermal and dilution effects from oxygen enrichment were greater than that from operation on oxygenated fuel.

Gas-phase in-cylinder mixing was examined by two different methods. The first method for observing mixing involved planar Mie scattering measurements of the instantaneous number density of silicon oil droplets which were introduced to the in-cylinder flow. The local value of the number density was assumed to be representative of the local gas concentration. Because the objective was to observe the rate in which gas concentration gradients change, to provide gradients in number density, droplets were admitted into the engine through only one of the two intake ports. Air only flowed through the other port. Three different techniques were used in analyzing the droplet images to determine the spatially dependent particle number density. Direct counting, a filtering technique, and autocorrelation were used and compared. Further, numerical experiments were performed with the autocorrelation method to check its effectiveness for determination of particle number density.

Two-Color imaging optics were developed and used to observe soot emission processes in a modern heavy-duty diesel engine. The engine was equipped with a common rail, electronically-controlled, high-pressure fuel injection system that is capable of up to four injection pulses per engine cycle. The engine was instrumented with an endoscope system for optical access for the combustion visualization. Multidimensional combustion and soot modeling results were used for comparisons to enhance the understanding and interpretation of the experimental data. Good agreement between computed and measured cylinder pressures, heat release and soot and NOx emissions was achieved. In addition, good qualitative agreement was found between in-cylinder soot concentration (KL) and temperature fields obtained from the endoscope images and those obtained from the multidimensional modeling.

A direct calibration has been performed on laser-induced fluorescence measurements of the oil film in a single cylinder air-cooled research engine by simultaneously measuring the minimum oil film thickness by the capacitance technique. At the minimum oil film thickness the capacitance technique provides an accurate measure of the ring-wall distance, and this value is used as a reference for the photomultiplier voltage, giving a calibration coefficient. This calibration coefficient directly accounts for the effect of temperature on the fluorescent properties of the constituents of the oil which are photoactive. The inability to accurately know the temperature of the oil has limited the utility of off-engine calibration techniques. Data are presented for the engine under motoring conditions at speeds from 800 - 2400 rpm and under varying throttle positions.

An engine emissions and performance study was conducted in conjunction with a series of experiments using a constant volume cold spray chamber. The purpose of the study was to explore the effects of number of holes and hole size on the emissions and performance of a direct injection heavy duty diesel engine. The spray experiments provide insight into the spray parameters and their role in the engine's combustion processes. The fuel system used for both the engine and spray chamber experiments was an electronically controlled, common rail injector. The injector nozzle hole size and number combinations used in the experiments included 225X8 (225 gm diameter holes with 8 holes in the nozzle), 260X6, 260X8, and 30OX6. The engine tests were conducted on an instrumented single cylinder version of the Caterpillar 3400 series heavy duty diesel engine. Data were taken with the engine running at 1600 RPM, 75% load.

Previous studies have shown that air motion affects the combustion process and therefore also the emissions in a DI diesel engine. Experimental studies indicate that higher engine speeds enhance the turbulence and this improves air and fuel mixing. However, there are few studies that address fundamental combustion related factors and possible limitations associated with very high speed engine operation. In this study, operation over a large range of engine speeds was simulated by using a multi-dimensional computer code to study the effect of speed on emissions, engine power, engine and exhaust temperatures. The results indicate that at higher engine speeds fuel is consumed in a much shorter time period by the enhanced air and fuel mixing. The shorter combustion duration provides much less available time for soot and NOx formations. In addition, the enhanced air/fuel mixing decreases soot and NOx by reducing the extent of the fuel rich regions.

In previous work the KIVA-II code has been modified to model modem DI diesel engines and their emissions of particulate soot and oxides of nitrogen (NOx). This work presents results from a program to further validate the NOx emissions models against engine experiments with a well characterized modern engine. To facilitate a simplified comparison with experiments, a single cylinder research version of the Caterpillar 3406 heavy duty DI diesel engine was retrofitted to run as a naturally-aspirated, propane-fueled, spark-ignited engine. The retrofit includes installing a low compression ratio piston with bowl, adding a gas mixer, replacing the fuel injector assembly with a spark plug assembly and adding spark and fuel stoichiometry control hardware. Cylinder pressure and engine-out NOx emissions were measured for a range of speeds, exhaust gas residual (EGR) fractions, and spark timing settings.

A laboratory-based fuel mixture system capable of delivering a range of fuel/air mixtures has been used to observe the effects of differing mixture characteristics on engine combustion through measurement and analysis of incylinder pressure and exhaust emissions. Fuel air mixtures studied can be classified into four different types: 1) Completely homogeneous fuel/air mixtures, where the fuel has been vaporized and mixed with the air prior to entrance into the normal engine induction system, 2) liquid fuel that is atomized and introduced with the air to the normal engine induction system, 3) liquid fuel that is atomized, and partially prevaporized but the air/fuel charge remains stratified up to introduction to the induction system, and 4) the standard fuel metering system. All tests reported here were conducted under wide open throttle conditions. A four-stroke, spark-ignited, single-cylinder, overhead valve-type engine was used for all tests.

To help understand the fundamental processes involved in direct injection, a research project was conducted using a single-cylinder, two-stroke research engine at a mid-speed, boat load operating condition. A 24 statistical factorial experimental design was applied. Of the factors tested at this operating condition, spray type was the most important factor affecting hydrocarbon emissions, followed by in-cylinder flow-related factors. Injection spray was also most important for nitrogen oxide emissions, carbon monoxide emissions, and efficiency. The dominant mechanism influencing the results was misfire, with other mechanisms present for specific responses.

Engine experiments have shown that with high-pressure multiple injections (two or more injection pulses per power cycle), the soot-NOx trade-off curves of a diesel engine can be shifted closer to the origin than those with the conventional single-pulse injections, reducing both soot and NOx emissions significantly. In order to understand the mechanism of emissions reduction, multidimensional computations were carried out for a heavy-duty diesel engine with multiple injections. Different injection schemes were considered, and the predicted cylinder pressure, heat release rate and soot and NOx emissions were compared with measured data. Excellent agreements between predictions and measurements were achieved after improvements in the models were made. The improvements include using a RNG k-ε turbulence model, adopting a new wall heat transfer model and introducing the nozzle discharge coefficient to account for the contraction of fuel jet at the nozzle exit.

In previous work, high injection pressures and multiple injections per engine stroke were shown to be effective at reducing the NOx and particulate emissions of DI Diesel engine combustion [1, 2]. A series of experiments were performed to study the effects of injection pressure, back pressure, and injection strategy on the spray characteristics for multiple injections. An injection system which was capable of multiple injections was used to introduce diesel fuel into a constant volume cold spray chamber. Parallel engine experiments were conducted using the same injectors as in this work [1, 2, 3]. In these engine tests, emissions (NOx and particulate) were measured. The engine experiments were used to develop the injector and chamber operating conditions for this work. The injection pressure was varied up to 90 MPa.