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Advanced diesel engines developed for the commercial market need to be adapted to the military requirements by OPERAS (Optimizing the injection pressure P, the Exhaust gas recirculation E, injection events Retard and/or Advance and the swirl ratio S). The different after treatment devices, already used or expected to be applied to diesel engines, require feed gases of appropriate properties for their efficient operation. To produce these gases some OPERAS are needed to control the diesel combustion process. Since military vehicles do not need the after treatment devices, the OPERAS of the commercial engines should be modified to meet the military requirements for high power density, better fuel economy, reduction of parasitic losses caused by the cooled EGR system, and reduction of invisible black and white smoke in the field.

EGR is a proven technology used to reduce NOx formation in both compression and spark ignition engines by reducing the combustion temperature. In order to further increase its efficiency the recirculated gases are subjected to cooling. However, this leads to a higher load on the cooling system of the engine, thus requiring a larger radiator. In the case of turbocharged engines the large variations of the pressures, especially in the exhaust manifold, produce a highly pulsating EGR flow leading to non-steady-state heat transfer in the cooler. The current research presents a method of determining the pulsating flow field and the instantaneous heat transfer in the EGR heat exchanger. The processes are simulated using the CFD code FIRE (AVL) and the results are subjected to validation by comparison with the experimental data obtained on a 2.5 liter, four cylinder, common rail and turbocharged diesel engine.

An evaluation has been made of the use of the diesel as an alternative engine in passenger cars. This includes the technological feasibility for meeting the different emission standards and the techniques for emission control. The emissions studied include both the presently regulated species--hydrocarbons, carbon monoxide, and nitrogen oxides--and the following nonregulated emissions: aldehydes, ammonia, smoke and particulates, polynuclear aromatics, and sulfur compounds. A comparison has been made between the emissions, performance and economy of currently produced diesel powered cars and gasoline powered cars. Other cars which are being developed and powered by the stratified charge, Wankel, and the gas turbine engines are also included in the comparison. Intrinsic problem areas in the diesel engine that need further research are also identified and discussed.

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.

A new tool has been used to arrive at appropriate split injection strategy for reducing the cranking period during the cold start of a multi-cylinder engine at decreasing ambient temperatures. The concept behind this tool is that the combination of different injection parameters that produce the highest IMEP should be able to improve the cold startability of the diesel engine. In this work the following injection parameters were considered: 1) injection timing, 2) split injection fraction, 3) dwell time and 4) total fuel mass injected per cycle. A commercial engine cyclic simulation code has been modified for diesel engine cycle simulation at lower ambient temperatures. The code was used to develop IMEP control maps. The maps were used to identify the parameters that would give the best IMEP. The strategies that have been identified have been validated experimentally in a multi-cylinder diesel engine equipped with a common rail fuel injection system.

All previous correlations of the ignition delay (ID) period in diesel combustion show a positive activation energy, which means that shorter ID periods are achieved at higher charge temperatures. This is not the case in the autoignition of most homogeneous hydrocarbons-air mixtures where they experience the NTC (Negative Temperature Coefficient ) regime in the intermediate temperature range, from about 800 K to 1000 K). Here, the autoignition reactions slow down and longer ID periods are experienced at higher temperatures. Accordingly the global activation energy for the autoignition reactions of homogeneous mixtures should vary from positive to negative values.

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.

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.

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.

The effects of the start/stop (S/S) transients on the Hybrid Electric Vehicle (HEV) operation and emissions are explored in this study. The frequency with which the engine starts and stops during an urban driving cycle is estimated by using the NREL's Advanced Vehicle Simulator software (ADVISOR). Furthermore, several tests were conducted on single-cylinder and multi-cylinder direct injection diesel engines in order to measure the cycle-resolved mole fractions of the hydrocarbons and nitric oxide exhaust emissions under frequent start/stop mode of operation. The frictional losses in engine in its entirety as well as in its components are also determined. In addition, the dynamic behavior of different high pressure fuel injection systems are investigated under the start and stop mode of operation.

The simulation of I.C. Engines operation, especially during transients, requires a fairly accurate estimation of the internal mechanical losses of the engine. The paper presents generic friction models for the main friction components of the engine (piston-ring-liner assembly, bearings and valve train), considering geometry of the engine parts and peculiarities of the corresponding lubrication processes. Separate models for the mechanical losses introduced by the injection system, oil and water pumps are also developed. All models are implemented as SIMULINK modules in a complex engine simulation code developed in SIMULINK and capable to simulate both steady state and transient operating conditions. Validation is achieved by comparison with measurements made on a four cylinder, common rail diesel engine, on a test bench capable to run controlled transients.

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 combustion and emission characteristics of a high speed, small-bore, direct injection, single cylinder, diesel engine are investigated using two different nozzles, a 430-VCO (0.171mm) and a 320 Mini sac (0.131mm). The experiments were conducted at conditions that represent a key point in the operation of a diesel engine in an electric hybrid vehicle (1500 rpm and light load condition). The experiments covered fuel injection pressures ranging from 400 to 1000 bar and EGR ratios ranging from 0 to 50%. The effects of nozzle hole geometry on the ignition delay (ID), apparent rate of energy release (ARER, ARHR), NOx, Bosch smoke unit (BSU), CO and hydrocarbons are investigated.

In view of the new regulations for diesel engine emissions, EGR is used to reduce the NOx emissions. Diluting the charge with EGR affects the autoignition, combustion as well as the regulated and unregulated emissions of diesel engines, under different operating conditions. This paper presents the results of an investigation on the effect of EGR on the global activation energy and order of the autoignition reactions, premixed and mixing-controlled combustion fractions, the regulated (unburned hydrocarbons, NOx, CO and particulates), aldehydes, CO2 and HC speciation. The experiments were conducted on two different direct injection, four-stroke-cycle, single-cylinder diesel engines over a wide range of operating conditions and EGR ratios.

I The effect of Cetane Number (CN) of the fuel and the addition of cetane improvers on the cold starting and white smoke emissions of a diesel engine was investigated. Tests were conducted on a single-cylinder, four-stroke-cycle, air-cooled, direct-injection, stand-alone diesel engine in a cold room at ambient temperatures ranging from 25 °C to - 5 °C. Five fuels were used. The base fuel has a CN of 49.2. The CN of the base fuel was lowered to 38.7 and 30.8 by adding different amounts of aromatic hydrocarbons. Iso-octyl nitrate is added to the high aromatic fuels in order to increase their CN to 48.6 and 38.9 respectively. Comparisons are made between the five fuels to determine the effect of CN and the additive on cylinder peak pressure, heat release rate, cold start-ability, combustion instability, hydrocarbon emissions and solid and liquid particulates.

An experimental study was conducted to characterize the dynamics and spray behavior of a wide range of minisac and Valve-Covered-Orifice (VCO) nozzles using a high-pressure diesel common-rail system. The measurements show that the resultant injection-rate is strongly dependent on common-rail pressure, nozzle hole diameter, and nozzle type. For split injection the dwell between injections strongly affects the second injection in regards to the needle lift profile and the injected fuel amount. The minisac nozzle can be used to achieve shorter pilot injections at lower common-rail pressures than the VCO nozzle. Penetration photographs of spray development in a high pressure, optical spray chamber were obtained and analyzed for each test condition. Spray symmetry and spray structure were found to depend significantly on the nozzle type.

Several dynamic parameters for the diagnosis of reciprocating combustion engines are investigated. Emphasis is made on the effect of sampling. The dynamic parameters include the frequency analysis, autocorrelation function, the frequency analysis of the autocorrelation function, variation of the angular velocity peaks, variation of the angular velocity depressions, variation of the angular velocity from before to after top dead center, velocity index and acceleration index. Two sampling techniques are used to measure the instantaneous angular velocity of a six cylinder, four-stroke-cycle diesel engine, under healthy and faulty conditions. The most effective dynamic parameters for engine diagnostics are determined.

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.

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.