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Experimental measurements of the instantaneous exhaust gas temperature, mass flowrate, and hydrocarbon concentration have been made in the exhaust of a single cylinder research engine. The temperature measurements were accomplished using an infrared optical technique and observing the radiation of the exhaust gas at the 4.4 μm band of CO2. Instantaneous exhaust gas mass flowrates were monitored by placing a restriction in the exhaust manifold and measuring the instantaneous pressures across the restriction. Time-resolved hydrocarbon concentrations were measured using a fast-acting sampling valve with an open time of 2 ms. From these measurements, the hydrocarbon mass flowrate is calculated as a function of crank angle.

In the jet-ignition prechamber stratified-charge spark-ignition engine, the fuel-air mixture at the time of combustion is non-uniform. Instantaneous exhaust mass flow rates and emission concentrations from this engine were measured and used to determine the degree to which this charge stratification persists in the products of combustion immediately downstream of the exhaust valve throughout the exhaust process. In all the cases studied no appreciable variations, during the exhaust process, were detected either in the air-fuel ratio of the exhaust gases as a function of time or in the instantaneous concentrations of CO2, O2 and NOx. The experimentally obtained instantaneous HC and CO concentrations in the exhaust, however, displayed large fluctuations and were used to study the sources of these two pollutants in this engine.

Measurements were made of exhaust histories of the following species: unburned hydrocarbons (HC), carbon monoxide, carbon dioxide, oxygen, and nitric oxide (NO). The measurements show that the exhaust flow can be divided into two distinct phases: a leading gas low in HC and high in NO followed by a trailing gas high in HC and low in NO. Calculations of time resolved equivalence ratio throughout the exhaust process show no evidence of a stratified combustion. The exhaust mass flow rate is time resolved by forcing the flow to be locally quasi-steady at an orifice placed in the exhaust pipe. The results with the quasi-steady assumption are shown to be consistent with the measurements. Predictions are made of time resolved mass flow rate which compare favorably to the experimental data base. The composition and flow histories provide sufficient information to calculate the time resolved flow rates of the individual species measured.

The Octane Index (OI) relates a fuel's knocking characteristics to a Primary Reference Fuel (PRF) that exhibits similar knocking characteristics at the same engine conditions. However, since the OI varies substantially with the engine operating conditions, it is typically measured at two standard conditions: the Research and Motor Octane Number (RON and MON) tests. These tests are intended to bracket the knock-limited operating range, and the OI is taken to be a weighted average of RON and MON: OI = K MON + (1-K) RON where K is the weighing factor. When the tests were established, K was approximately 0.5. However, recent tests with modern engines have found that K is now negative, indicating that the RON and MON tests no longer bracket the knock-limited operating conditions. Experiments were performed to measure the OI of different fuels in a modern engine to better understand the role of fuel sensitivity (RON-MON) on knock limits.

This paper describes the results of experimental and computer simulation studies of the combustion process in the prechamber three-valve stratified-charge engine. Prechamber and main-chamber pressure data and matched computer simulation calculations are used to determine the effects of variations in overall air/fuel ratio, engine speed and load, and prechamber volume and orifice diameter on the parameters which define the combustion process (spark advance for optimum torque, ignition delay, combustion duration), on cylinder pressure diagrams (mean main-chamber pressure, mean pressure difference across the orifice, and cycle-by-cycle pressure fluctuations) and on exhaust emissions. General correlations are derived from the data for the shape of the combustion rate profile and the extent of the combustion duration.

To understand the effects of crevices on the engine-out hydrocarbon emissions, a series of engine experiments was carried out with different piston crevice volumes and with simulated head gasket crevices. The engine-out HC level was found to be modestly sensitive to the piston crevice size in both the warmed-up and the cold engines, but more sensitive to the crevice volume in the head gasket region. A substantial decrease in HC in the cold-to-warm-up engine transition was observed and is attributed mostly to the change in port oxidation.

Two aspects of the dispersion of pollutants from aircraft are reviewed. The first is the dispersal of aircraft exhaust emissions in the vicinity of airports; the second is the dispersal of exhaust trails in the upper atmosphere. Techniques available for modeling this dispersal and how they might be applied to the airport problem are discussed. Field studies of airport pollution are then reviewed to assess current pollutant levels around airports and the aircraft's contribution to those levels. The possibility of contrail formation from jet emissions at high altitude is then considered and the effect of uncertainties in the trail mixing processes evaluated.

A performance model of a Wankel engine is developed which performs a leakage mass balance, accounts for heat transfer and flame quenching, and predicts the mass fraction burned as a function of chamber pressure. Experiments were performed on a production Wankel engine to obtain chamber pressure-time diagrams, and engine performance and emissions data. Model predictions of mass burned, global heat transfer, and hydrocarbon emission gave good agreement with measurements. Predictions of oxides of nitrogen are higher than measurements, especially at low loads. This is thought to be due to the adiabatic core gas assumption in the model. The need for a Wankel boundary layer study is identified.

An improved theoretical model that predicts the nitric oxide concentration in the exhaust of a spark-ignition engine has been evaluated over a wide range of fuel-air ratios, percentage of exhaust gas recycled, and engine speed. Experiments were carried out in a standard CFR single-cylinder engine. Comparison of the measured and calculated exhaust nitric oxide concentrations shows good agreement over all operating conditions. It is shown that in lean mixtures, nitric oxide concentrations freeze early in the expansion stroke. For rich mixtures, freezing occurs later after all the charge has been burned and substantial nitric oxide decomposition takes place. In addition, effects of exhaust gas recirculation on flame speed, ignition delay, and cycle-to-cycle pressure variations were evaluated. A simple model relating cycle-to-cycle variations with changes in ignition delay is presented.

This study examines the scaling between engine performance, engine configuration, and engine size and geometry, for modern spark-ignition engines. It focuses especially on design features that impact engine breathing. We also analyze historical trends to illustrate how changes in technology have improved engine performance. Different geometric parameters such as cylinder displacement, piston area, number of cylinders, number of valves per cylinder, bore to stroke ratio, and compression ratio, in appropriate combinations, are correlated to engine performance parameters, namely maximum torque, power and brake mean effective pressure, to determine the relationships or scaling laws that best fit the data. Engine specifications from 1999 model year vehicles sold in the United States were compiled into a database and separated into two-, three-, and four-valves-per-cylinder engine categories.

1 Downsizing and turbocharging a spark-ignited engine is becoming an important strategy in the engine industry for improving the efficiency of gasoline engines. Through boosting the air flow, the torque is increased, the engine can thus be downsized, engine friction is reduced in both absolute and relative terms, and engine efficiency is increased. However knock onset with a given octane rating fuel limits both compression ratio and boost levels. This paper explores the operating limits of a turbocharged engine, with various gasoline-ethanol blends, and the interaction between compression ratio, boost levels, and spark retard, to achieve significant increases in maximum engine mean effective pressure and efficiency.

The fate of hydrocarbon species in the exhaust systems of spark-ignition engines is an important part of the overall hydrocarbon emissions problem. In this investigation models were developed for the instantaneous heat transfer, fluid mixing, and hydrocarbon oxidation in an engine exhaust port. Experimental measurements were obtained for the instantaneous cylinder pressure and instantaneous gas temperature at the exhaust port exit for a range of engine operating conditions. These measurements were used to validate the heat transfer model and to provide data on the instantaneous cylinder gas state for a series of illustrative exhaust port hydrocarbon oxidation computations as a function of engine operating and design variables. During much of the exhaust process, the exhaust port heat transfer was dominated by large-scale fluid motion generated by the jet-like flow at the exhaust valve.

In order to understand better the operation of spark-ignition engines during the warm-up period, a computer model had been developed which simulates the thermal processes of the engine. This model is based on lumped thermal capacitance methods for the major engine components, as well as the exhaust system. Coolant and oil flows, and their respective heat transfer rates are modeled, as well as friction heat generation relations. Piston-liner heat transfer is calculated based on a thermal resistance method, which includes the effects of piston and ring material and design, oil film thickness, and piston-liner crevice. Piston/liner crevice changes are calculated based on thermal expansion rates and are used in conjunction with a crevice-region unburned hydrocarbon model to predict the contribution to emissions from this source.

The oil control ring is the most critical component for oil consumption and friction from the piston system in internal combustion engines. Three-piece oil control rings are widely used in Spark Ignition (SI) engines. However, the dynamics and lubrication of three piece oil control rings have not been thoroughly studied from the theoretical point of view. In this work, a model was developed to predict side sealing, bore sealing, friction, and asperity contact between rails and groove as well as between rails and the liner in a Three Piece Oil Control Ring (TPOCR). The model couples the axial and twist dynamics of the two rails of TPOCR and the lubrication between two rails and the cylinder bore. Detailed rail/groove and rail/liner interactions were considered. The pressure distribution from oil squeezing and asperity contact between the flanks of the rails and the groove were both considered for rail/groove interaction.

An experimental study was carried out that qualitatively examined the mixture preparation process in port fuel injected engines. The primary variables in this study were intake valve lift, intake valve timing, injector spray quality, and injection timing. A special visualization engine was used to obtain high-speed videos of the fuel-air mixture flowing through the intake valve, as well as the wetting of the intake valve and head in the combustion chamber. Additionally, videos were taken from within the intake port using a borescope to examine liquid fuel distribution in the port. Finally, a simulation study was carried out in order to understand how the various combinations of intake valve lifts and timings affect the flow velocity through the intake valve gap to aid in the interpretation of the videos.

The liquid fuel entry into the cylinder and its subsequent behavior through the combustion cycle were observed by a high speed CCD camera in a transparent engine. The videos were taken with the engine firing under cold conditions in a simulated start-up process, at 1,000 RPM and intake manifold pressure of 0.5 bar. The variables examined were the injector geometry, injector type (normal and air-assisted), injection timing (open- and closed-valve injection), and injected air-to-fuel ratios. The visualization results show several important and unexpected features of the in-cylinder fuel behavior: 1) strip-atomization of the fuel film by the intake flow; 2) squeezing of fuel film between the intake valve and valve seat at valve closing to form large droplets; 3)deposition of liquid fuel as films distributed on the intake valve and head region. Some of the liquid fuel survives combustion into the next cycle.

The occurrence of liquid fuel in the cylinder of automotive internal combustion engines is believed to be an important source of exhaust hydrocarbon (HC) emissions, especially during the warm-up process following an engine start up. In this study a Phase Doppler Particle Analyzer (PDPA) has been used in a transparent flow visualization combustion engine in order to investigate the phenomena which govern the transport of liquid fuel into the cylinder during a simulated engine start up process. Using indolene fuel, the engine was started up from room temperature and run for 90 sec on each start up simulation. The size and velocity of the liquid fuel droplets entering the cylinder were measured as a function of time and crank angle position during these start up processes. The square-piston transparent engine used gave full optical access to the cylinder head region, so that these droplet characteristics could be measured in the immediate vicinity of the intake valve.

Liquid fuel flow into the cylinder an important source of hydrocarbon (HC) emissions of an SI engine. This is an especially important HC source during engine warm up. This paper examines the phenomena that determine the inflow of liquid fuel through the intake valve during a simulated start-up procedure. A Phase Doppler Particle Analyzer (PDPA) was used to measure the size and velocity of liquid fuel droplets in the vicinity of the intake valve in a firing transparent flow-visualization engine. These characteristics were measured as a function of engine running time and crank angle position during four stroke cycle. Droplet characteristics were measured at 7 angular positions in 5 planes around the circumference of the intake valve for both open and closed-valve injection. Additionally the cone shaped geometry of the entering liquid fuel spray was visualized using a Planar Laser Induced Fluorescence (PLIF) setup on the same engine.

Experiments were performed to identify the knock trends of lean hydrocarbon-air mixtures, and such mixtures enhanced with hydrogen (H2) and carbon monoxide (CO). These enhanced mixtures simulated 15% and 30% of the engine's gasoline being reformed in a plasmatron fuel reformer [1]. Knock trends were determined by measuring the octane number (ON) of the primary reference fuel (mixture of isooctane and n-heptane) supplied to the engine that just produced audible knock. Experimental results show that leaner operation does not decrease the knock tendency of an engine under conditions where a fixed output torque is maintained; rather it slightly increases the octane requirement. The knock tendency does decrease with lean operation when the intake pressure is held constant, but engine torque is then reduced.

The influence of charge motion and fuel injection characteristics on diesel combustion was studied in a rapid compression machine (RCM), a research apparatus that simulates the direct-injection diesel in-cylinder environment. An experimental data base was generated in which inlet air flow conditions (temperature, velocity, swirl level) and fuel injection pressure were independently varied. High-speed movies using both direct and shadowgraph photography were taken at selected operating conditions. Cylinder pressure data were analyzed using a one-zone heat release model to calculate ignition delay times, premixed and diffusion burning rates, and cumulative heat release profiles. The photographic analysis provided data on the liquid and vapor penetration rates, fuel-air mixing, ignition characteristics, and flame spreading rates.