Thomas W. Ryan

Cetane numbers of branched and straight-chain fatty esters determined in an ignition quality tester☆☆

The cetane number, a widely used diesel fuel quality parameter related to the ignition delay time (and combustion quality) of a fuel, has been applied to alternative diesel fuels such as biodiesel and its components. In this work, the cetane numbers of 29 samples of straight-chain and branched C1 –C 4 esters as well as 2-ethylhexyl esters of various common fatty acids were determined. The cetane numbers of these esters are not significantly affected by branching in the alcohol moiety. Therefore, branched esters, which improve the cold-flow properties of biodiesel, can be employed without greatly influencing ignition properties compared to the more common methyl esters. Unsaturation in the fatty acid chain was again the most significant factor causing lower cetane numbers. Cetane numbers were determined in an ignition quality tester (IQT) which is a newly developed, automated rapid method using only small amounts of material. The IQT is as applicable to biodiesel and its components as previous cetane-testing methods. Published by Elsevier Science Ltd.

The effects of vegetable oil properties on injection and combustion in two different diesel engines

Four different vegetable oils, each in at least 3 different stages of processing, have been characterized according to their physical and chemical properties, their injection and atomization characteristics, and their performance and combustion characteristics in both a direct-injection and an indirect-injection diesel engine. The injection and atomization characteristics of the vegetable oils are significantly different than those of petroleum-derived diesel fuels, mainly as the result of their high viscosities. Heating the oils, however, results in spray characteristics more like those observed with diesel fuel. The 2 engine types demonstrated different sensitivities to the composition of the various oils. The combustion characteristics and the durability of the direct-injection engine were affected by the oil composition. The indirect-injection engine, however, was not greatly affected by composition. Two different preliminary specifications have been proposed: a stringent specification including compositional requirements for direct-injection engines, and a less stringent specification for indirect-injection engines. The specifications are discussed in terms of the data and the rationale used in their development. Some precautions concerning the application of the specifications are also presented.

Fuel Requirements for HCCI Engine Operation

Researchers at Southwest Research Institute (SwRI) have been working for the past several years on the fundamental and practical aspects of homogeneous charge compression ignition (HCCI) operation of reciprocating engines. Much of the work has focused on the use of diesel fuel. The work at SwRI has, however, demonstrated that there are fundamental limitations on the use of current diesel fuels in HCCI engines. The results of engine and constant volume combustion bomb experiments are presented and discussed. The engine experiments were used to identify important fuel properties that must be included in a fuel specification for HCCI fuels. The primary properties relate -to the distillation characteristics and the ignition characteristics. The engine test provided preliminary guidance on the distillation requirements and an indication of the important ignition requirements. The constant volume combustion bomb experiments were performed in an effort to define a new fuel property that will serve to characterize the ignition property of a fuel in an HCCI engine.

The Heavy Duty Gasoline Engine - A Multi-Cylinder Study of a High Efficiency, Low Emission Technology

SwRI has developed a new technology concept involving the use of high EGR rates coupled with a high-energy ignition system in a gasoline engine to improve fuel economy and emissions. Based on a single-cylinder study [1], this study extends the concept of a high compression ratio gasoline engine with EGR rates > 30% and a high-energy ignition system to a multi-cylinder engine. A 2000 MY Isuzu Duramax 6.6 L 8-cylinder engine was converted to run on gasoline with a diesel pilot ignition system. The engine was run at two compression ratios, 17.5:1 and 12.5:1 and with two different EGR systems - a low-pressure loop and a high pressure loop. A high cetane number (CN) diesel fuel (CN=76) was used as the ignition source and two different octane number (ON) gasolines were investigated - a pump grade 91 ON ((R+M)/2) and a 103 ON ((R+M)/2) racing fuel. The results showed that the stock, 17.5:1 compression ratio (CR) was unsuitable for operation except at light (<50%) loads with the peak BMEPs of 700 kPa on 91 ON fuel and 1000 kPa on 103 ON fuel. The engine-out BSNOx ranged from 0.76 to 2.35 g/kW-hr with brake thermal efficiencies (BTE) between 26-38% over the load range. At 12.5:1 CR, the peak BMEPs were much higher, 1260 kPa on 91 ON and 1720 kPa on 103 ON. The engine-out BSNOx ranged from 0.03 to 2.10 g/kW-hr with BTEs between 23-37% over the load range. With the addition of a 3-way catalyst, made possible by stoichiometric operation, the possibility exists for extremely low emissions at diesel-like fuel economies. These results show that the technology has the potential to return the efficiency of a modern diesel engine (equipped with aftertreatment devices) with the low emissions of a light-duty gasoline engine.

Diesel Fuel Ignition Quality as Determined in a Constant Volume Combustion Bomb

The ignition delay times of forty-two different fuels were measured in a constant volume combustion bomb. The measurements were performed at three different initial air temperatures using fuels ranging from the primary reference fuels for cetane rating to complex mixtures of coal-derived liquids. The ignition delay times were examined in terms of the classical definitions of the physical and chemical delay times. The previously used definitions were found to be inadequate, and new definitions have been proposed. The total ignition delay times were studied in the context of providing a means for rating the ignition quality of the fuels. Fuel ignition quality rating schemes are discussed, including one based on the current cetane number scale as well as one based on a new scale which includes a measure of the sensitivity of the various fuels to the air temperature.

Engine and Constant Volume Bomb Studies of Diesel ignition and Combustion

The importance of the ignition process is reflected in the fact that the only combustion property that is specified for diesel fuel is the ignition delay time as indicated by the cetane number. The objective of the work described in this paper was to determine the relationship between the ignition process as it occurs in an actual engine, to ignition in a constant volume combustion bomb. The ultimate goal is to develop a new procedure for rating the ignition and combustion quality of fuels for diesel engines. The short-term goal, and an interim step in the development effort, is to establish the bomb approach for determining cetane number.

The Effects of Fuel Properties and Composition on Diesel Engine Exhaust Emissions - A Review

Due to the cost and mobility advantages of diesel-powered mine vehicles over electric vehicles, it is anticipated that the diesel engine will become more widely used in underground mines in this country. Concern has arisen, however, over the impact of diesel exhaust emissions on the air quality in the underground mine environment. A literature search has been conducted, however, the data base is relatively small and the results highly dependent on engine type and operating conditions. Engine studies on a typical mine diesel are necessary to draw quantitative conclusions regarding the reduction of emissions, especially particulates and NO/sub 2/ which have not been generally addressed in previous studies. 52 refs.

Engine knock rating of natural gases: methane number

A procedure has been developed and documented for determining the methane number of gaseous fuels. The methane number provides an indication of the knock tendency of the fuel. An experimental test matrix was designed for quantifying the effects of ethane, propane, butane, and CO[sub 2]. A unique gas mixing and control system was developed to supply test gases to the engine and to control the equivalence ratio and engine operation. The results of the experiments agreed well with the limited data published in the literature. Predictive equations were developed for the methane number (MN) of gaseous fuels using the gas composition. The forms of these equations are suitable for incorporation in a computer program or a spread-sheet.

Heavy-Duty Diesel Engine Emissions Tests Using Special Biodiesel Fuels

A 2003 heavy-duty diesel engine (2002 emissions level) was used to test a representative biodiesel fuel as well as the methyl esters of several different fatty acids. The fuel variables included degree of saturation, the oxygen content, and carbon chain length. In addition, two pure normal paraffins with the corresponding chain lengths of two of the methyl esters were also tested to determine the impact of chain length. The dependent variables were the NO x and the particulate emissions (PM). The results indicated that the primary fuel variable affecting the emissions is the oxygen content. The emissions results showed that the highest oxygen content test fuel had the lowest emissions of both NO x and PM. As compared to the baseline diesel fuel the NO x emissions were reduced by 5 percent and the PM emissions were reduced by 83 percent.

The Heavy-Duty Gasoline Engine - An Alternative to Meet Emissions Standards of Tomorrow

A technology path has been identified for development of a high efficiency, durable, gasoline engine, targeted at achieving performance and emissions levels necessary to meet heavy-duty, on-road standards of the foreseeable, future. Initial experimental and numerical results for the proposed technology concept are presented. This work summarizes internal research efforts conducted at Southwest Research Institute. An alternative combustion system has been numerically and experimentally examined. The engine utilizes gasoline as the fuel, with a combination of enabling technologies to provide high efficiency operation at ultra-low emissions levels. The concept is based upon very highly-dilute combustion of gasoline at high compression ratio and boost levels. Results from the experimental program have demonstrated engine-out NO x emissions of 0.06 g/hp/hr, at single-cylinder brake thermal efficiencies (BTE) above thirty-four percent. Multi-cylinder, 3-way catalyst equipped versions of this engine are estimated to provide NO x emissions of approximately 0.003 g/hp/hr at efficiencies approaching thirty-nine percent.