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Experiments have been conducted in a laminar flow system and in a research engine to investigate the effect of additives on the combustion of gasoline-like fuels. The purpose of the laminar system is to enable rapid screening of additives to determine which, if any, have an enhancing effect on the early stages of combustion, especially under conditions of poor fuel vaporization which exist during cold-start in a spark ignited engine and which make flame propagation difficult to start and sustain. The base fuel used in the laminar and engine systems was a 9 component mixture formulated to simulate those components of gasoline expected to be present in the vapor phase in the intake system of an engine under cold-start conditions. In the laminar system, the pre-mixed, pre-vaporized fuel-air mixture is ignited and a time history of the combustion generated, hydroxyl radical chemiluminescence is recorded.

An experimental study was conducted to determine if an organic fuel additive could reduce engine out hydrocarbon and NOx emissions. A production four cylinder spark ignited engine with throttle body fuel injection was used for the study. A full boiling range base fuel, an additized base fuel, a base fuel with methyl tertiary butyl ether (MTBE) and a base fuel with MTBE and additive were used in the engine tests. Additive concentration was 1/2% by mass. Hydrocarbon and NOx measurements were recorded for 11 load/speed conditions. Hydrocarbon speciation data was taken at two of these conditions. The data from the experiments was analyzed in a pair-wise fashion for the fuels with and without the additive to determine whether statistically significant changes occurred.

A nondimensional representation for a four stroke spark ignition engine was obtained that included the transient charging and exhaust effects. Two basic advantages accrued from this approach; the design and operating parameters that evolved from the nondimensional approach are truly basic in nature, which makes the computer solution more universally applicable to all engines. The inclusion of the transient effects made the representation more realistic and of particular value in the study of engine breathing problems. The effect of valve timing, cam design, valve dimensions, and inlet temperature on engine performance were studied with the computer model.

The cycle-by-cycle variations of the combustion process of a spark ignition engine result in cycle-by-cycle (CBC) variations of the cylinder pressure development histories. Many investigators have postulated that these pressure variations are due to CBC variations of the gas motion near the spark plug at the time of ignition. This investigation was undertaken to determine if such a correlation does in fact exist. The CBC combustion variations of a CFR-RDH engine were examined in terms of the CBC pressure development histories. A constant-temperature hot-film probe was used to determine the velocity variations from cycle to cycle of the motored engine in the vicinity of the spark plug at the crank angles at which ignition would take place under firing conditions. The standard deviations of the gas velocity near the spark plug were correlated to the standard deviations of the crank angle at which maximum pressure occurred for different operating variables.

Engine and vehicle tailpipe emissions can be measured in laboratories equipped with engine dynamometers and chassis dynamometers, respectively. In addition to laboratory testing, there is an increase in interest to measure on-road vehicle emissions using portable emissions measurement systems in order to determine real-driving emissions. Current methods to quantify engine, vehicle tailpipe, and real-driving emissions include the raw continuous, dilute continuous, and dilute bag measurement methods. Although the dilute bag measurement method is robust, recent improvements to the raw and dilute continuous measurement methods can account for the time delay between the probe tip and analyzer in addition to gas transport dynamics in order to reliably recover the tailpipe concentration signals. These improvements significantly increase the reliability of results using the raw and dilute continuous measurement methods, making them possible alternatives to the bag method.

Dimethyl Ether (DME) is a potential ultra-clean diesel fuel. Its unique characteristics require special handling and accommodation of its low viscosity and low lubricity. In this project, DME was blended with diesel fuel to provide sufficient viscosity and lubricity to permit operation of a 7.3 liter turbodiesel engine in a campus shuttle bus with minimal modification of the fuel injection system. A pressurized fuel delivery system was added to the existing common rail injection system on the engine, allowing the DME-diesel fuel blend to be circulated through the rail at pressures above 200 psig keeping the DME in the liquid state. Fuel exiting the rail is cooled by finned tubed heat exchangers and recirculated to the rail using a gear pump. A modified LPG tank (for use on recreational vehicles) stores the DME- diesel fuel blend onboard the shuttle bus.

The gas-phase exhaust emissions which resulted when a variably timed, variable mass of water was injected directly into the cylinder of a spark-ignition engine are reported. The experimental setup and the procedure used in the investigation are also described. Conclusions are drawn with regard to the optimum injection timing and amount of water introduced. Generally, direct-cylinder injection of water reduces NO, increases unburned HC, and does not effect CO and CO2. For a fixed-ignition timing, power also deteriorates. Another finding of this investigation is that direct-cylinder injection does result in NO reductions of better than 85% while using about one-third the mass of water required by manifold injection to effect a similar reduction.

Cycle-to-cycle variations of the combustion process of spark ignition engines, usually observed as peak pressure variations, are a phenomenon whose causes have not yet been identified with certainty. For investigating whether or not there is a relationship between physical cycle characteristics, such as peak pressure, and exhaust gas composition, a sampling system was developed which collects bag samples from specified cycles only. It consists of an analog portion for obtaining pressure and rate-of-pressure change signals, a digital logic portion for discriminating between signals according to selected criteria, and an electrically actuated sampling valve in the engine exhaust system. Since signal analysis and discrimination are instantaneous, gas sampling is done during the exhaust stroke of the same cycle for which the logic generated the command to sample. The system is described in detail and its use is illustrated with an example.

The lean misfire limit air-fuel ratio of a spark ignition engine was extended by various modifications of the intake and ignition systems. The effects of long duration spark, extended spark plug gap projections and gap widths, and a vaned collar intake valve are reported. These modifications allowed for reliable operation up to air-fuel ratios of 24:1. The experimental apparatus and procedure used in this study are described. Conclusions are drawn concerning the optimization of the various modifications to extend the lean misfire limit and reduce the exhaust emissions. In general, all modifications extended the lean misfire limit, but increased gap width had the most profound effect. In all cases, the exhaust emissions were reduced by extension of the lean misfire limit.

In this study, the performance and emissions of a 4 cylinder 2.5L light-duty diesel engine with methane fumigation in the intake air manifold is studied to simulate a dual fuel conversion kit. Because the engine control unit is optimized to work with only the diesel injection into the cylinder, the addition of methane to the intake disrupts this optimization. The energy from the diesel fuel is replaced with that from the methane by holding the engine load and speed constant as methane is added to the intake air. The pilot injection is fixed and the main injection is varied in increments over 12 crank angle degrees at these conditions to determine the timing that reduces each of the emissions while maintaining combustion performance as measured by the brake thermal efficiency. It is shown that with higher substitution the unburned hydrocarbon (UHC) emissions can increase by up to twenty times. The NOx emissions decrease for all engine conditions, up to 53%.

In this study, performance and emissions characteristics of an LPG direct injection (DI) engine with a rotary distributor pump were examined by using cetane enhanced LPG fuel developed for diesel engines. Results showed that stable engine operation was possible for a wide range of engine loads. Also, engine output power with cetane enhanced LPG was comparable to diesel fuel operation. Exhaust emissions measurements showed NOx and smoke could be reduced with the cetane enhanced LPG fuel. Experimental model vehicle with an in-line plunger pump has received its license plate in June 2000 and started high-speed tests on a test course. It has already been operated more than 15,000 km without any major failure. Another, experimental model vehicle with a rotary distributor pump was developed and received its license plate to operate on public roads.