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Ion current sensors have been considered for the feedback electronic control of gasoline and diesel engines and for onboard vehicles powered by both engines, while operating on their conventional cycles or on the HCCI mode. The characteristics of the ion current signal depend on the progression of the combustion process and the properties of the combustion products in each engine. There are large differences in the properties of the combustible mixture, ignition process and combustion in both engines, when they operate on their conventional cycles. In SI engines, the charge is homogeneous with an equivalence ratio close to unity, ignition is initiated by an electric spark and combustion is through a flame propagating from the spark plug into the rest of the charge.

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.

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.

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.

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 variation of the crankshaft's speed is influenced by the action of the cylinders and shall reflect the contribution of each cylinder to the total engine output. At the same time, the speed variation is influenced by the torsional stiffness of the cranks, the mass moments of inertia of the reciprocating mechanisms and the average speed and load of the engine. As the result, the variation of angular motion of the crankshaft is complex, each particular influence changing its importance as speed and load are modified. The diagnostic method presented in the paper is based on the analysis of the amplitudes and phases of the lowest harmonic orders of the measured speed and is capable to determine the average Indicated Mean Effective Pressure (IMEP), to detect nonuniformities in cylinder operation and to identify the faulty cylinder(s).

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.

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.

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.

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.

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.

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 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.

Cycle-to-cycle cylinder pressure variation has been observed in a CFR prechamber diesel engine when low ignition quality (low cetane number) fuels are burned. A statistical analysis of this phenomenon for various fuels and blends with cetane numbers as low as zero has been made. Operating conditions used were those specified by the ASTM Cetane Method for rating diesel fuels, in which the inlet air temperature is 150°F. Additional analysis was made at increased inlet air temperatures of 250°F and 350°F. The cycle-to-cycle variation has been characterized by the variation in the ignition (or pressure rise) delay time. It has been found to increase sharply as fuel cetane number is decreased below 20. The variation in dynamic injection timing was also measured and correlated with that for ignition delay.

A new approach referred to as (P-ω) method, has been developed at Wayne State University to determine the instantaneous friction and its components in internal combustion engines. The method is based on the fact that the instantaneous cylinder gas forces and the instantaneous frictional, inertia and load forces cause the instantaneous variation in the flywheel angular velocity. The instantaneous total friction forces have been computed for a single diesel engine, under idling conditions. A breakdown of the friction into its components and a formulation for each component has been made. By applying linear regression, correlations between the individual components of the friction losses and the different parameters have been developed. The components are classified into two categories: piston assembly losses and crankcase assembly losses.

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.

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.

The correlations between the physical properties and autoignition parameters of several alternate fuels have been examined. The fuels are DF-2 and its blends with petroleum derived fuels, coal derived fuels, shale derived fuels, high aromatic naphtha sun-flower oils, methanol and ethanol. A total of eighteen existing correlations are discussed. An emphasis is made on the suitability of each of the correlations for the development of electronic controls for diesel engines when run on alternate fuels. A new correlation has been developed between the cetane number of the fuels and its kinematic viscosity and specific gravity.

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.