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Technical Paper

Modeling the Effects of EGR and Injection Pressure on Emissions in a High-Speed Direct-Injection Diesel Engine

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.
Technical Paper

Effect of Imposed Faults on a Distributor Injection System

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.
Technical Paper

Correlation of Air Charge Temperature and Ignition Delay for Several Fuels in a Diesel Engine

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.
Technical Paper

Ignition Delay in Diesel Engines

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.
Technical Paper

A Mathematical Model for the Mass Transfer and Combustible Mixture Formation Around Fuel Droplets

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.
Technical Paper

Characterization and Simulation of a Unit Injector

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.
Technical Paper

Advanced Low Temperature Combustion (ALTC): Diesel Engine Performance, Fuel Economy and Emissions

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.
Technical Paper

Effect of Injection Pressure and Swirl Motion on Diesel Engine-out Emissions in Conventional and Advanced Combustion Regimes

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.