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The objective of this work is to develop a strategy to reduce the penalties in the diesel engine performance, fuel economy and HC and CO emissions, associated with the operation in the low temperature combustion regime. Experiments were conducted on a research high speed, single cylinder, 4-valve, small-bore direct injection diesel engine equipped with a common rail injection system under simulated turbocharged conditions, at IMEP = 3 bar and engine speed = 1500 rpm. EGR rates were varied over a wide range to cover engine operation from the conventional to the LTC regime, up to the misfiring point. The injection pressure was varied from 600 bar to 1200 bar. Injection timing was adjusted to cover three different LPPCs (Location of the Peak rate of heat release due to the Premixed Combustion fraction) at 10.5° aTDC, 5 aTDC and 2 aTDC. The swirl ratio was varied from 1.44 to 7.12. Four steps are taken to move from LTC to ALTC.

The fuel injection pressure and the swirl motion have a great impact on combustion in small bore HSDI diesel engines running on the conventional or advanced combustion concepts. This paper examines the effects of injection pressure and the swirl motion on engine-out emissions over a wide range of EGR rates. Experiments were conducted on a single cylinder, 4-valve, direct injection diesel engine equipped with a common rail injection system. The pressures and temperatures in the inlet and exhaust surge tanks were adjusted to simulate turbocharged engine conditions. The load and speed of the engine were typical to highway cruising operation of a light duty vehicle. The experiments covered a wide range of injection pressures, swirl ratios and injection timings. Engine-out emission measurements included hydrocarbons, carbon monoxide, smoke (in Bosch Smoke Units, BSU) and NOx.

An experimental investigation was conducted on a small-bore, high-speed diesel engine to study the effect of different operating parameters on combustion and engine-out emissions in the conventional and low temperature regimes. For the conventional diesel combustion, the spray behavior is analyzed and a differentiation is made between the conditions in the small-bore and the larger bore quiescent chamber engines. The effects of the injection pressure, exhaust gas recirculation (EGR), injection timing and swirl ratio (SR) on combustion and engine-out emission are investigated. The trade-off between NOx and smoke, measured in Bosch smoke unit, (BSU), is investigated with a special attention to the low temperature combustion regime, (LTC). The results showed that the LTC regime could be reached at fairly high EGR rates under all the injection pressures investigated in this work. The margin for the variation in EGR was limited just before the misfiring EGR.

The performance of the Common Rail diesel injection system (CRS) is investigated experimentally in a single cylinder engine and a test rig to determine the cycle-to-cycle variation in the injection pressure and its effects on the needle opening and rate of fuel delivery. The engine used is a single cylinder, simulated-turbocharged diesel engine. Data for the different injection and performance parameters are collected under steady state conditions for 35 consecutive cycles. Furthermore, a mathematical model has been developed to calculate the instantaneous fuel delivery rate at various injection pressures. The experimental results supported with the model computations indicated the presence of cycle-to-cycle variations in the fuel injection pressure and needle lift. The variations in the peak-cylinder gas pressure, rate of heat release, cylinder gas temperature and IMEP are correlated with the variation in the injection rate.

Integrated control strategies for the O.P.E.R.A.S. (Optimization of injection Pressure, EGR ratio, injection Retard or Advance and Swirl ratio) are demonstrated. The strategies are based on an investigation of combustion and emissions in a small bore, high speed, direct injection diesel engine. The engine is equipped with a common rail injection system and is tested under simulated turbocharged engine conditions at two loads and speeds that represent two key operating points in a medium size HEV vehicle. A new phenomenological model is developed for the fuel distribution in the combustion chamber and the fractions that are injected prior to the development of the flame, injected in the flame or deposited on the walls. The investigation covered the effect of the different operating parameters on the fuel distribution, combustion and engine-out emissions.

Experiments were conducted to investigate the characteristics of a common rail fuel injection system using a flow rate test rig and a single cylinder research diesel engine. Experiments covered speeds and loads typical to engine conditions under Hybrid Electric Vehicle operation. Different injection modes were investigated including main injection, main-post injection and pilot-main injection. The analysis indicated that the common rail fuel pressure affects all the injection parameters including the start of fuel delivery, its duration and amount under all modes of injection. Also, the pressure waves produced in the system have an impact on the operation of the nozzle-needle and fuel delivery particularly in the main-post injection mode.

Experimental data is used in conjunction with multi-dimensional modeling in a modified version of the KIVA-3V code to characterize the emissions behavior of a high-speed, direct-injection diesel engine. Injection pressure and EGR are varied across a range of typical small-bore diesel operating conditions and the resulting soot-NOx tradeoff is analyzed. Good agreement is obtained between experimental and modeling trends; the HSDI engine shows increasing soot and decreasing NOx with higher EGR and lower injection pressure. The model also indicates that most of the NOx is formed in the region where the bulk of the initial heat release first takes place, both for zero and high EGR cases. The mechanism of NOx reduction with high EGR is shown to be primarily through a decrease in thermal NOx formation rate.

More stringent regulations have been enforced over the past few years on diesel exhaust emissions. White smoke emission, a characteristic of diesel engines during cold starting, needs to be controlled in order to meet these regulations. This study investigates the sources and constituents of white smoke. The effects of fuel properties, design and operating parameters on the formation and emissions of white smoke are discussed. A new technique is developed to measure the real time gaseous hydrocarbons (HC) as well as the solid and liquid particulates. Experiments were conducted on a single cylinder direct injection diesel engine in a cold room. The gaseous HC emissions are measured using a high frequency response flame ionization detector. The liquid and solid particulates are collected on a paper filter placed upstream of the sampling line of the FID and their masses are determined.

The instantaneous frictional torque (IFT) of many components of a single cylinder diesel engine was determined by considering the forces acting on each component and the resulting change in the angular velocity. The IFT for the basic system, consisting of the crankshaft with the flywheel and oil pump, was first determined. The effect of adding each of the following to the basic system was determined: balancer shaft, cam shaft, piston with different ring combinations, inlet valve, exhaust valve and fuel injection pump. All the tests were conducted without gas pressure in the cylinder in a coast down mode. The results indicated the contribution of each component in the total frictional torque and its mode of lubrication. The energy absorbed by the valve springs and released back to the system was clearly Identified. The effect of speed on IFT and energy lost in friction was determined.

Diesel engines have to face the prospect of running on heavy and/or low cetane fuels in the future because of the expected changes in base stock and demand. The effect of physical properties and composition of fuels on the ignition delay and cetane rating is examined. The experiments were conducted on fuels having a very wide range of physical properties and C.N., in a CFR engine. The ignition delay is measured under the standard ASTM D-613 procedure and under varying needle opening pressures, and coolant temperatures. The ignition delay of some fuels is found to be dependent on the physical properties and composition of the fuels in addition to the cetane number. The cetane rating according to ASTM-D613 procedure is found to take place under hot engine conditions with a single stage ignition process. At lower compression ratios, a two stage ignition was observed.

The autoignition and combustion of four fuels having different distillation ranges and cetane numbers have been investigated in a single cylinder, direct injection diesel engine, at ambient temperatures between 30°C and −30°C. The effects of ambient air temperature on the compression pressure, compression temperature, blow-by mass fraction, ignition delay and cycle-to-cycle variation have been determined. The results indicate that the chemical preignition processes rather than the physical processes are the controlling processes in the ignition delay in diesel engines, even at very low ambient temperatures. Low ignition quality fuels produce cycle-to-cycle variations in their autoignition at low ambient temperatures.

A study of the burning velocity and performance in a CFR S.I. engine when run on methanol-indolene blends has been completed. The parameters investigated are the burning velocity, brake mean effective pressure, brake specific fuel consumption, thermal efficiency, volumetric efficiency and MBT spark advance over a wide range of compression ratios (5.0 to Knock Limited Compression Ratio) and methanol concentrations (0 to 100%). The charge is heated in the inlet manifold to a uniform temperature of 120 F for all the blends. The results indicated that by adding methanol to indolene, the turbulent and laminar burning velocities increases, MBT spark timing need to be retarded, brake mean effective pressure and volumetric efficiency decrease. Adding methanol to indolene results in an increase in thermal efficiency, Knock Limited Compression Ratio and specific fuel consumption.

A study of the burning velocities in Methanol-Indolene-Air Mixtures has been completed in a CFR engine. The investigation included measurements of ignition delay, combustion interval, and flame speed over a wide range of compression ratios (5.0 to Knock Limited Compression Ratio) and methanol concentration (0 to 100%). The results indicated that by adding methanol to indolene, ignition delay, combustion interval and MBT (Minimum Advanced for Best Torque) spark advance decreased. Adding methanol to indolene results in an increase in flame speed, burning velocity and the Knock Limited Compression Ratio.

The characteristics of the diesel engine unit injector were studied both theoretically and experimentally. The transient fuel pressure in the unit injector was indirectly measured by using strain gauges placed in different locations on the drive train, between the cam and plunger. The events which take place during the injection process were analyzed and the effects of several design and operating variables on the different injection parameters were determined. Computer simulation showed a fairly good agreement between computed and experimental results.

The effects of several faults on different parameters in a distributor injection system are studied both theoretically and experimentally. The faults imposed on a healthy system are: fuel leaks between the pump and injector, improper adjustment of the injector opening pressure, a broken or missing injector spring, plugged nozzle holes, and a stuck-closed needle. The injector parameters examined include maximum fuel pressures reached at different locations in the system, needle lift, injection lag, and injection rate.

The vapor diffusion and the combustible mixture formation around evaporating fuel droplets are studied. The formulas derived for the droplet temperature and vapor concentration profiles take into consideration the unsteady period before the droplet reaches its equilibrium temperature. In this model the droplet is assumed to be suddenly brought into contact with a high temperature oxidizing atmosphere. The ignition delay is considered equal to the period of time from the start of heating up to the time of formation of a stoichiometric mixture at the ignition location around the droplet. Computations are made for the temperature history, concentration history, and the ignition delay for iso-octane droplets evaporating in air. The droplet sizes considered are between 1120 and 1520 μ. The air pressure is 14.7 psia, and the air temperatures are 1095-1390 F. The comparison between the results of the present model and previous experimental results showed favorable agreement.

The purpose of this paper is to develop some concepts for the mechanisms of emission formation during the combustion of liquid fuel sprays injected in swirling air. An emphasis is made on finely dispersed sprays used in open chamber diesel engines. The emissions studied are the unburned hydrocarbons, carbon monoxide, aldehydes, smoke particulates, and oxides of nitrogen. The spray is considered to be composed of a group of droplets of different sizes. The behavior of these droplets is determined by studying a mathematical model for droplet evaporation and ignition. The spray is then divided into regions, depending on the mechanism of combustion in each region. The emissions formed in each region are examined. The concepts developed for the formation of the different emissions in the spray are used for a qualitative analysis of some engine experimental data.

A correlation between the ignition delay, based on the start of pressure rise due to combustion, and the mean air charge temperature has been obtained for diesel, “CITE,” and gasoline fuels. The experimental work was done on a single cylinder open combustion chamber research engine. The intake air temperature was varied over a wide range from atmospheric to about 750 F. The experimental data indicated that the best correlation of the ignition delay and the reciprocal of the absolute temperature is of an exponential form. The apparent activation energy for the three fuels was found to have a straight line relationship with the cetane number of the fuel.

Possible mechanisms for smoke formation in the diesel engine are discussed. Emphasis is placed on the effects of some engine and fuel factors on carbon formation during the course of combustion, including cetane number, fuel volatility, air charge temperature, and after-injection. The tests were made with a single-cylinder, open chamber research engine, with three fuels, covering a wide range of inlet air temperatures and pressures. There is evidence that smoke intensity increased with increase in the cetaine number of the fuels with inlet air temperatures near atmospheric. Increase in the air charge temperature caused an increase in smoke intensity for volatile fuels and had an opposite effect on less volatile fuels for the open chamber engine used. The smoke intensity was found to increase dramatically with after-injection, with all other parameters kept constant. The concept that flame cooling is the main cause for smoke formation is examined.

The ignition delay in diesel combustion has been studied in a turbulent chamber engine. The criteria used to define the end of this period are the pressure rise and illumination due to combustion. The pressure rise delay is generally shorter and more reproducible than the illumination delay. The effect of the following factors on the ignition delay were studied: cylinder pressure, fuel/air ratio, fuel injection pressure, cooling water temperature, and engine speed. Data concerning the effect of cylinder pressure on the pressure rise delay period, at constant air temperature, were correlated and compared with previous experimental results. The analysis indicated that the pressure rise delay is affected by physical and chemical factors as well as thermodynamic parameters that control the several forms of energy during the delay period.