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The application of sophisticated analytical techniques for the design of spark-ignition engines has brought about the need for detailed information on the heat transfer processes in these engines. This study utilized time-resolved heat-flux measurements, heat-release analysis and high-speed flame photography to investigate experimentally the combustion and heat-transfer characteristics of an optically accessible single-cylinder engine. The engine has a pent-roof shaped combustion chamber with two intake and two exhaust valves. The primary engine variable examined was the intake-flow configuration which was varied by means of shrouded valves. The measured local heat-flux histories on the combustion side of the head were found to have significant cycle-to-cycle and spatial variations, which are believed to be caused primarily by corresponding variations in combustion.

This paper is a continuation of an earlier paper, which examined the steady-state internal heat transfer in the exhaust system of a diesel powered, light-duty vehicle. The present paper deals with the heat transfer of the exhaust system during two types of transient testing, as well as, the estimation of the exhaust systems external heat transfer. Transient heat transfer was evaluated using: a simple fuel-step transient under constant speed and the New European Driving Cycle (NEDC). The thermal response of the external walls varied considerably for the various components of the exhaust system. The largest percent difference between the measured temperatures and the corresponding quasi-steady estimates were about 10%, which is attributed to thermal storage. Allowing for thermal storage resulted in an excellent agreement between measurements and analysis.

This study is an experimental and computational investigation of the influence of injection timing, fuel spray orientation, and in-cylinder air motion on the combustion, fuel economy, and engine-out emissions of a single-cylinder, 2-valve, spark-ignition direct-injection (SIDI) engine, operating under stratified-charged conditions. For the best compromise between fuel consumption, combustion stability, engine-out hydrocarbon emissions and smoke, the engine required relatively retarded injection timings (in comparison to other charge- or wall-controlled DI engines), high swirl levels, and a spray orientation that is directed towards the intake-valve side and targets the ridge wall of the piston.

Local transient heat-flux measurements and heat-release analyses were employed to investigate the effects of introducing swirl or tumble fluid motion during the intake stroke on the combustion and heat-transfer characteristics of a single-cylinder spark-ignition engine. In general, swirl or tumble motion decreased the period of flame development and increased the peak rate of heat release, but, surprisingly, it increased the period of combustion. The latter increase was the result of comparatively low rates of fuel burning during the last stages of combustion. Swirl or tumble motion also significantly increased the local heat flux on the cylinder head. The highest peak heat flux was obtained for tumble motion. The observed increase in heat flux is attributed to the resultant increase in the mean velocity and in the turbulent intensity of the gases in the combustion chamber, which, in turn, augment the rate of heat release and the effective convective heat-transfer coefficient.

This paper presents an experimental study of the cycle-averaged, local surface heat transfer, from the exhaust gases to a straight pipe extension of the exhaust port of a four-cylinder spark-ignition (SI) engine, over a wide range of engine operating conditions, from 1000 rpm, light load, through 4000 rpm, full load. The local steady-state heat flux was well correlated by a Nusselt-Reynolds number relationship that included entrance effects. These effects were found to be the major contributor to the local heat transfer augmentation. The Convective Augmentation Factor (CAF), which is defined as the ratio of the measured heat flux to the corresponding heat flux for fully-developed turbulent pipe flow, was found to decrease with increasing Reynolds number and increasing axial distance from the entrance of the test section.

This study investigated the effects of three fuel delivery systems (port fuel injection with production injectors, port fuel injection with air-assisted injectors and a premixed, prevaporized fuel system) on engine-out hydrocarbon (HC) emissions from a four-cylinder spark ignition engine. Comparative tests were run at three part-load conditions and a wide range of EGR. Other engine parameters examined were intake-air and coolant temperatures, and injection timing. The observed effects of injection timing on HC emissions were related to the intake-flow events, which, in turn, affect in-cylinder fuel evaporation and combustion.

High-speed schlieren photography was employed to study air-fuel mixing and combustion in several two-dimensional prechambers that represented a 1980 GM-oldsmobile diesel prechamber and modifications thereof. The experiments were performed in a Rapid Compression Machine. A computational study was also undertaken to model these experiments using a two-dimensional computer code. The computational study also considered a Ricardo Comet V swirl chamber, in addition to the above chambers. The computations gave predictions of the full two-dimensional transient flow field during the compression stroke in the absence of injection or combustion. This study showed that the prechamber flow is dominated by the incoming jet. As a result the vortex, which is formed due to the nearly tangential jet entry, initially is confined to part of the chamber and not centered in the chamber.

The potential sources of hydrocarbon (HC) emissions from a single-cylinder, divided-chamber diesel engine were investigated in this study. To evaluate the relative importance of these sources, the variations of HC emissions with engine speed, air-fuel ratio, combustion timing, intake-air temperature, coolant temperature and oil temperature were examined. Included in the diagnostics of this investigation were: ignition-delay measurements, combustion-chamber surface temperature measurements and heat-release modeling. Lubricating oil was found to contribute significantly to HC emissions. In addition, the results suggested that bulk quenching of flame and non-flame reactions is a primary source of HC emissions. On the other hand, lean mixing during the ignition delay period and wall interactions appear to be secondary sources.

An air-gap-insulated piston designed for reduced heat loss was evaluated by examining its influence on the coolant heat rejection, engine performance and exhaust emissions of a single-cylinder divided-chamber diesel engine. At 1000 and 1500 r/min engine speed, use of the low-heat-rejection (LHR) piston resulted in a reduction in total coolant heat rejection ranging from 3% at light load to 5-7% at full load, in a general reduction in hydrocarbons, carbon monoxide and smoke emissions, in an increase in oxides of nitrogen, and in a significant improvement in brake specific fuel consumption only at light loads. It was estimated that the LHR piston design reduced the piston-crown surface heat transfer by an amount equivalent to from 3.5% (full load) to 5.5% (light load) of the input fuel energy at 1000 r/min.

In this study, the performance and emissions characteristics of an uncooled, thermally insulated diesel that utilized an optimized injector-tip configuration are examined. When the uncooled engine was compared to a conventional water-cooled engine at the same brake power and airflow, the uncooled engine had equal or superior fuel consumption, significantly higher nitric oxide emissions, and significantly lower smoke and particulate emissions. The dramatic reduction in smoke emitted by the uncooled engine was not observed in studies reported earlier. This smoke reduction is attributed to the high gas temperatures and increased rates of air-fuel mixing that augmented the rate of oxidation of the soot particles when the injector tip was optimized for the uncooled engine and airflow was adjusted to match that of the cooled engine. Heat-release analyses showed that the uncooled engine had less premixed combustion and significantly shorter combustion duration than the water-cooled engine.

Suppression of the heat rejection to the coolant was achieved by the use of an air-gap-insulated piston, an antechamber that was partially insulated by an air-gap, and high-temperature coolant (ethylene glycol at 120°C). In comparison to the standard configuration (STD) of the engine, the low-heat-rejection configuration (LHR) resulted in a small increase in brake thermal efficiency for light-load conditions, in a reduction in volumetric efficiency, in an increase in the exhaust energy, and in an increase in the heat rejection to the lubricating oil. Heat-release analysis performed on the two engines showed higher overall fuel burning rates, and consequently shorter combustion durations, in the LHR engine than in the STD engine. This is believed to cause the observed higher nitric oxide emissions. Also, the LHR engine was found to have higher hydrocarbon emissions but slightly lower particulate emissions.

The influence of the number and the size of the fuel-injector orifices and their opening pressure on the performance and emissions of an uncooled, thermally insulated diesel engine was experimentally investigated. Increasing the number of orifices was generally found to decrease the Brake Specific Fuel Consumption (BSFC) and smoke emissions but to increase the nitric-oxide (NO) emissions. Increasing the number of orifices resulted in a slight increase in premixed burning and in a substantial decrease in the duration of combustion. Increasing the orifice size increased the BSFC and smoke emissions but decreased the NO emissions. The heat-release characteristics were not significantly altered, however. Finally, increasing the opening pressure of the injector increased the BSFC and smoke emissions and decreased the NO emissions of the uncooled engine.