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Several mechanisms are discussed to understand the particulate matter (PM) characterization in a high speed, direct injection, single cylinder diesel engine using low sulfur diesel fuel. This includes their formation, size distribution and number density. Experiments were conducted over a wide range of injection pressures, EGR rates, injection timings and swirl ratios, therefore covering both conventional and low temperature combustion regimes. A micro dilution tunnel was used to immediately dilute a small part of the exhaust gases by hot air. A Scanning Mobility Particle Sizer (SMPS) was used to measure the particulate size distribution and number density. Particulate mass was measured with a Tapered Element Oscillating Microbalance (TEOM). Analysis was made of the root cause of PM characterization and their relationship with the combustion process under different operating conditions.

One of the most challenging problems in diesel engines is to reduce unburned HC emissions that appear as (white smoke) during cold starting. In this paper the research is carried out on a 4-cylinder diesel engine with a common rail fuel injection system, which is able to deliver multiple injections during cold start. The causes of combustion failure at lower temperature limits are investigated theoretically by considering the rate of heat release. The results of this clearly indicate that in addition to low cranking engine speed, heat transfer and blow-by losses at lower ambient temperatures, fuel injection events would contribute to the failure of combustion. Also, combustion failure takes place when the compression temperature is lower than some critical value. Based on these results, split-main injection strategy was applied during engine cold starting and validated by experiments in a cold room at lower ambient temperatures.

Several mechanisms are discussed to understand the formation of both regulated and unregulated emissions in a high speed, direct injection, single cylinder diesel engine using low sulphur diesel fuel. Experiments were conducted over a wide range of injection pressures, EGR rates, injection timings and swirl ratios. The regulated emissions were measured by the standard emission equipment. Unregulated emissions such as aldehydes and ketones were measured by high pressure liquid chromatography and hydrocarbon speciation by gas chromatography. Particulate mass was measured with a Tapered Element Oscillating Microbalance (TEOM). Analysis was made of the sources of different emission species and their relationship with the combustion process under the different operating conditions. Special attention is given to the low temperature combustion (LTC) regime which is known to reduce both NOx and soot. However the HC, CO and unregulated emissions increased at a higher rate.

Engine-out HC emissions were investigated during cold and hot starts. The tests were conducted at room temperature, on a new Chrysler 2.4-L, 4-cylinder, 16-valve, DOHC, multipoint-port-fuel-injection gasoline engine. Real time engine-out HC emissions were measured using Cambustion Fast Response Flame Ionization Detector (FRFID). Sources of unburned hydrocarbon emissions were discussed in details. Unburned hydrocarbons emitted during the cold-start were much higher than the hot-start. Cylinder-to-cylinder variation was investigated. A fuel inventory program was used to characterize total injected fuel, burned fuel, unburned HC, and fuel unaccounted for (mainly accumulated fuel in the engine system and CO). A fuel interrupt test was run to examine the possibility of burning the leftover fuel after the fuel shut-off. The contribution of the cold and hot start modes in engine-out HC emissions was determined.

The emissions trade-off and combustion characteristics of a high speed, small-bore, direct injection, single cylinder, diesel engine are investigated at three different load conditions. The experiments covered a wide range of parameters including the injection pressure, exhaust gas recirculation (EGR) rate and swirl ratio (Sw). The effects of each parameter on the ignition delay (ID), apparent rate of energy release (ARER), NOx, Bosch smoke unit (BSU), CO and hydrocarbons are investigated. The results show that the NOx emission dropped continuously with the increase in EGR (up to 55%), but with increasing smoke emission in a classical trade-off relationship. The increase in injection pressure generally reduced smoke with NOx penalty; however, the NOx penalty decreased at higher EGR. There also appears to be an increase in the cool flame intensity at the high EGR rates. Applying swirl at high EGR rate and high injection pressure conditions further reduced smoke emissions.

The nozzle configuration for an injector is known to have an important effect on the fuel atomization. A comprehensive experimental and numerical investigation has been performed to determine the influence of various internal geometries on the primary spray breakup and development using the electronically controlled high-pressure diesel injection systems. Different types of multi-hole minisac and VCO nozzles with cylindrical and tapered geometries, and different types of single-hole nozzles with defined grades of Hydro Grinding (HG) were investigated. The global characteristics of the spray, including spray angle, spray tip penetration and spray pattern were measured from the spray images with a high-speed drum camera. A long-distance microscope with a pulsed-laser as the optical shutter was used to magnify the diesel spray at the nozzle hole vicinity. A CFD analysis of the internal flow through various nozzle geometries has been carried out with a commercial code.

Combustion instability is investigated during the cold starting of a single cylinder, direct injection, 4-stroke-cycle, air-cooled diesel engine. The experiments covered fuels of different properties at different ambient air temperatures and injection timings. The analysis showed that the pattern of misfiring (skipping) is not random but repeatable. The engine may skip once (8-stroke-cycle operation) or twice (12-stroke-cycle operation) or more times. The engine may shift from one mode of operation to another and finally run steadily on the 4-stroke cycle. All the fuels tested produced this type of operation at different degrees. The reasons for the combustion instability were analyzed and found to be related to speed, residual gas temperature and composition, accumulated fuel and ambient air temperature.

The instantaneous frictional torque (IFT) of the engine and the piston-ring assembly frictional force (PRAFF) were determined during cranking and starting of a direct injection single cylinder diesel engine. The measurements included the cylinder gas pressure, the instantaneous torque of the electric starter, the angular velocity of the crankshaft and the axial force on the connecting rod. The engine and piston friction were determined every crank angle degree for all the cycles from the time the starter was engaged to the time the engine reached the idling speed. The data was analyzed and a comparison was made between the friction in successive cycles.

The UBHC emissions during cold starting need to be controlled in order to meet the future stringent standards. This requires a better understanding of the characteristics of the time resolved UBHC signal measured by a high frequency FID and its phasing with respect to the valve events. The computer program supplied with the instrument and currently used to compute the phase shift has many uncertainties due to the unsteady nature of engine operation during starting. A new technique is developed to measure the in-situ phase shift of the UBHC signal under the transient thermodynamic and dynamic conditions of the engine. The UBHC concentration is measured at two locations in the exhaust manifold of one cylinder in a multicylinder port injected gasoline engine. The two locations are 77 mm apart. The downstream probe is positioned opposite to a solenoid-operated injector which delivers a gaseous jet of hydrocarbon-free nitrogen upon command.

An experimental and numerical study was carried out to simulate the diesel spray behavior during cold starting conditions inside two single-cylinder optically accessible engines. One is an AVL single-cylinder research diesel engine converted for optical access; the other is a TACOM/LABECO engine retrofitted with mirror-coupled endoscope access. The first engine is suitable for sophisticated optical diagnostics but is constrained to limited consecutive fuel injections or firings. The second one is located inside a micro-processor controlled cold room; therefore it can be operated under a wide range of practical engine conditions and is ideal for cycle-to-cycle variation study. The intake and blow-by flow rates are carefully measured in order to clearly define the operation condition. In addition to cylinder pressure measurement, the experiment used 16-mm high-speed movie photography to directly visualize the global structures of the sprays and ignition process.

An experimental method for determining the Instantaneous Frictional Torque (IFT) using pressure transducers on every cylinder and speed measurements at both ends of the crankshaft is presented. The speed variation measured at one end of the crankshaft is distorted by torsional vibrations making it difficult to establish a simple and direct correlation between the acting torque and measured speed. Using a lumped mass model of the crankshaft and modal analysis techniques, the contributions of the different natural modes to the motion along the crankshaft axis are determined. Based on this model a method was devised to combine speed measurements made at both ends of the crankshaft in such a way as to eliminate the influence of torsional vibrations and obtain the equivalent rigid body motion of the crankshaft. This motion, the loading torque and the gas pressure torque are utilized to determine the IFT.

A detailed analysis has been made on the Cetane Scale presently used to rate the autoignition quality of fuels. The effect of the increase in temperature and pressure, as a result of increasing the compression ratio, on the ignition delay has been theoretically and experimentally analyzed. It has been found that the ignition delay is more sensitive to air temperature than air pressure. The sensitivity increases with the drop in the cetane number of the fuel. Many techniques have been examined to modify the present cetane scale. A modified scale has been developed by raising the inlet temperature from 150°F to 350°F without changing the rest of the rating technique. The modified scale is very effective in extending the scale to zero cetane number and is able to rate the low ignition quality fuels.

Many diagnostic parameters have been studied for the detection of malfunctions in two types of diesel injection systems: the unit injector and the distributor pump system. It has been found that the peak fuel pressure in the unit injector pressure chamber (measured by a strain gage mounted on the injector rocker arm), and the peak fuel pressure in the line near the injector on the distributor injection system are very useful parameters for fault diagnosis. Figures and charts relating the fuel peak pressure and engine speed have been developed to identify a healthy as well as a faulty injection system.

A study was conducted on a direct-injection, single-cylinder, research-type diesel engine to determine the effect of adding ethanol to diesel fuel on the ignition delay period. The tests covered the whole range of ethanol-DF2 blends: from 100% ethanol to 100% DF2. The test parameters were: the ethanol content, the intake-air properties, and the equivalence ratio. The ignition delay was measured by detecting the beginning of injection and the occurrence of a detectable pressure rise. The present results show that, for ethanol-DF2 blends, the pressure-rise delay decreases by increasing both the intake-air pressure and the intake-air temperature, and increases by increasing the ethanol content in the blend. Ignition delay correlations were developed in terms of air temperature, air pressure, and ethanol volumetric fraction. The global activation energy was determined and correlated with the cetane number for each blend.

This paper describes the development and results of a mathematical model for a single cylinder, naturally-aspirated, direct-injection diesel engine, used to study the effect of compression ratio on the different performance parameters. The parameters investigated include; thermal and mechanical efficiency, ignition delay, mean effective pressure, maximum cylinder pressure, mechanical friction, and blowby. The model simulates a full thermodynamic cycle and considers the intake and exhaust processes, instantaneous heat transfer, instantaneous friction, and instantaneous blowby. Based on the model results, a prediction of an optimum CR for the engine is made.

A mathematical model Is developed to study the transient behavior of a four-stroke, single cylinder naturally-aspirated, DI diesel engine during cranking and starting. The model simulates the full thermodynamic cycle of the engine and includes detailed sub-models for the intake and exhaust gas flow processes, autoignition combustion, heat transfer, mechanical friction, blowby, and engine dynamics. The model considers the period of time from starter on until the engine reaches the idle speed. Experimental data and results obtained from the engine are used to calibrate and validate the model. A comparison of results from the model and the experiments generally show good agreement for the starting conditions investigated.

Many problems can develop from the uncontrolled fuel injection during cranking and starting of diesel engines. Some of the problems are related to excessive wear as a result of the high peak pressures reached upon combustion after misfiring, the relatively low rotating speeds and the lack of formation of a lubricating oil film between the interacting surfaces. Another problem is the emission of high amounts of unburned hydrocarbons and white smoke. Experimental results are given for a single cylinder and a multicylinder diesel engine, for the instantaneous angular velocity and cylinder pressures from the starter-on point until the engine fires. The causes of misfiring during cranking are investigated. The role of the increased blow-by gases on the autoignition process at the low cranking speeds is analyzed both analytically and experimentally. The contribution of the instantaneous angular velocity at the time of injection, on the autoignition process is investigated.

This paper introduces a diagnostic technique for the detection of misfiring cylinders in internal combustion engines. The technique requires the analysis of the instantaneous angular velocity of an engine flywheel. The results show that the mean cyclic acceleration, maximum variation in angular velocity, and the cyclic period of acceleration can be used as a measure for the mean net torque and the mean net expansion pressure torque produced by each cylinder. The proposed technique has proven to be effective in identifying a faulty cylinder using efficient and simple computations.

A new formulation is developed for the ignition delay (ID) in diesel engines to account for the effect of piston motion on the global autoignition reaction rates. A differentiation is made between the IDe measured in engines and IDv, measured in constant volume vessels. In addition, a method is presented to determine the coefficients of the IDe correlation from actual engine experimental data. The new formulation for IDe is applied to predict the misfiring cycles during the cold starting of diesel engines at different low ambient temperatures. The predictions are compared with experimental results obtained on a multi-cylinder heavy-duty diesel engine.

An experimental study was carried out to visualize the spray and combustion inside an AVL single-cylinder research diesel engine converted for optical access. The injection system was a hydraulically-amplified electronically-controlled unit injector capable of high injection pressure up to 180 MPa and injection rate shaping. The injection characteristics were carefully characterized with injection rate meter and with spray visualization in high-pressure chamber. The intake air was supplied by a compressor and heated with a 40kW electrical heater to simulate turbocharged intake condition. In addition to injection and cylinder pressure measurements, the experiment used 16-mm high-speed movie photography to directly visualize the global structures of the sprays and ignition process. The results showed that optically accessible engines provide very useful information for studying the diesel combustion conditions, which also provided a very critical test for diesel combustion models.