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To ignite very lean natural gas mixture it is necessary to use prechambers. The extension of lean limit of a combustion system is given by citing an example. The orifice diameter from the prechamber to the main chamber has a strong effect. The magnitude of the effect for one particular example is shown. The prechamber has another very beneficial effect, that is it increases the turbulence, which has the effect of producing more power at the same fuel to air ratio mixture. A generalized curve is given where BSNOx (grams of NOx per brake HP-HR) vs. λ (A/F/(A/F)S) is given for natural gas. A section is given to illustrate the importance of having a uniform mixture (homogeneous) to keep NOx values to a minimum. Two plots are given, one based on NOx formed in the prechamber is frozen when it emerges from the prechamber, and the other the NOx emerging is equilibrated during burning. These plots can be used to compare engine data.

To ignite very lean natural gas mixture it is necessary to use prechambers. The extension of lean limit of a combustion system is given by citing an example. The orifice diameter from the prechamber to the main chamber has a strong effect. The magnitude of the effect for one particular example is shown. The prechamber has another very beneficial effect, that is it increases the turbulence, which has the effect of producing more power at the same fuel to air ratio mixture. A generalized curve is given where BSNOx (grams of NOx per brake HP-HR) VS. λ(A/F/(A/F)S) is given for natural gas. A section is given to illustrate, the importance of having a uniform mixture (homogeneous) to keep NOx values to a minimum. Two plots are given, one based on NOx formed in the prechamber is frozen when it emerges from the prechamber, and the other the NOx emerging is equilibrated during burning. These plots can be used to compare engine data.

A tutorial write up is first presented to give the behavior of droplet burning (diesel engines) and natural gas burning for dual fuel and natural gas burning engines. By citing literature, it is shown that for each droplet there is a certain amount of generated. The combination of droplet burning (in the prechamber) and with natural gas in the main chamber with a good turbocharger system Danyluk, Ref. 1, has shown that NOx can be controlled to 1.0 gram per brake-horsepower hour while maintaining high brake thermal efficiency. This author has generalized the information in die design of PCCI (Prechamber Compression Ignition) engine systems. A design chart is given to size the prechamber.

Additional data has been analyzed on the effect of engine size on thermal efficiency. The comparison has been expanded to show the trends separately for engines developed by several different manufacturers. The data confirm the conclusion that engines below 2.0 liters per cylinder seem to deteriorate in fuel economy faster than would have been predicted from the behavior of larger engines. It is postulated that such deterioration results from a combination of less than optimum fuel spray, wall wetting, and perhaps a greater heat transfer loss than was anticipated. The paper focuses on engines in the size range under two liters per cylinder and addresses some of the problems to be resolved. Means for generating and controlling fuel spray and injection rate shape are presented along with experimental data on fuel sprays and engine combustion.

Review of the theories, observations, and trends presented in Part I of this set of papers leads to the projection of certain aspects of injection sprays, mixture preparation, and combustion which may be designed to enhance diesel engine efficiency and reduce unwanted emissions. The basic concept is that control of the size, distribution and time of introduction of fuel droplets will result in a predictable optimized combustion event. Burning rate is controlled by droplet size and not by injection rate. The results of the ideal combustion and mixture preparation models are compared with experimental data and show good correlation. The preference for high-pressure, short-duration, non-wall-wetting and uniformly distributed fuel sprays coupled with controlled fast diffusion burning is clearly evident. With high injection rates, it may be desirable to trade swirl rate for additional combustion air.

The per cylinder displacement in cubic centimeters (PCDICC) vs. brake specific fuel consumption (BSFC) have been plotted for both DI and IDI diesel engines. The smallest and largest PCDICC are 25.7 to 2,000,000. It was found for the DI engines that the lowest to the highest (BSFC) ranged from approximately 155 to 450. In terms of ratios these turn out to be about 2.9. Reasons for the increase in BSFC with decrease in PCDICC are presented. Background material are presented to help in explaining the trends experienced. Boundary conditions of the injected fuel as to duration, drop size, and their effect on BSFC, emissions are postulated.

The degree of “imperfect mixing” induced by the macro mixing in the turbulent eddy scale is estimated by evaluating the probability density function versus the equivalence ratio. The procedure was proposed to evaluate the simplified discrete probability density function based on the measured average gas concentrations. The patterns of probability density function for three typical turbulent diffusion flames, with and without swirl, are presented to characterize the degree of imperfect mixing depending on the flame configurations and positions in the flame.

An experimental apparatus, based on laser light diffraction, was developed and used to study changes in drop size distribution during a single injection, as well as from injection-to-injection, in a diesel fuel spray in room air. A model-independent numerical procedure was developed to infer drop size distribution from measured diffracted light energy. It is believed that spray deflectors, used to reduce optical density in the core of the spray, considerably influenced drop sizes. Data collected from undisturbed outer edges of the spray indicated that large numbers of sequential sprays must be sampled to accurately determine true distribution mean and dispersion parameters. Drop size distributions at all sampled locations were bi-modal, with spray axis locations exhibiting the greatest fractions of small drops. During a single spray, at a fixed location in space, the Sauter Mean Diameter varied approximately inversely as the fuel line pressure.

Products from reacting propane and air have been constructed for reactions under many different conditions. It is proposed in this paper to use C2H2 as a temperature indicator for diffusion flame. Published experimental data containing species is analyzed using the various plots to estimate the degree of mixing and sooting.

Apparatus was developed to obtain time and spatially resolved gas samples from the displacement volume of a reciprocating engine. This equipment was used to study the distribution of fuel and combustion products, with emphasis on the origins and formation mechanisms of hydrocarbons, in a single-cylinder Texaco L-141 TCP engine run on heptane. Two of three potential hydrocarbon sources were identified. Frozen hydrocarbon compositions found near the head surface after 15°CA were attributed to wall quenching. Heptane found at all sampling locations prior to the start of fuel injection was associated with a source of fuel on the bowl surface.

From recently published papers, mostly from Japanese authors, which deals with soot containing flames, the author chose certain experimental results contained in these papers to support the idea that 2000 to 2400°K is the temperature range in diffusion flames where the flame contains soot. The maximum soot concentration in diffusion flames occurs at a temperature of about 2150°K. From this peak, soot concentration containing flame at 2150, the soot concentration drops off on both sides until at about 1950 and at 2400 the flame contains negligible soot. Supportive arguments are presented and backed by published experimental data.

In engine combustion chambers, where the overall fuel-air mixture is stoichiometric or leaner, the effect of localized pockets or zones of stoichiometric or richer mixture are presented. Possible explanations for the existence of CO, with soot in exhaust are offered. Also the effect of localized zones of richer than stoichiometric have on the thermal efficiency are also presented. Experimental data from literature are used to support the ideas.

This investigation dealt with the experimental determination of a select chemical specie - the hydroxyl radical - present in the non-flamed end gases ahead of the flame front in a spark-ignited engine operating under conditions of both normal and knocking combustion. Concentration measurements of the hydroxyl radical present in the end gases were obtained with the technique of resonance absorption spectroscopy utilizing a broadband-output, frequency-tunable, flashlamp-pumped, organic-dye laser. The dye laser and a photographic spectrometer were placed on opposite sides of a single cylinder research engine and the combustion chamber of the engine was fitted with quartz windows that allowed the dye-laser light pulse to pass through the end gas region and into the spectrometer. The dye laser was pulsed once at a present crankangle during the combustion cycle recording the 2∑+-2∏ electronic transition absorption spectrum on film.

Monochromatic ultraviolet (UV) absorbance, temperature, and pressure histories of unburned gas in a single cylinder CFR engine under motored, fired, and autoignition conditions were recorded on a multichannel magnetic tape recorder. Isooctane, cyclohexane, ethane, n-hexane, n-heptane, 75 octane number (ON), 50 ON, and 25 ON blends of primary reference fuels (PRF) were studied. Under knocking or autoignition conditions a critical absorbance at 2600 A was found, whose magnitude was independent of engine operating variables and dependent only on the knock resistance of the fuel. This absorbance increased rapidly when a certain temperature level was exceeded during the exothermic preflame reactions.