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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.

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.

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.

An integrated vehicle system simulation has been developed to take advantage of advances in physical process and component models, flexibility of graphical programming environments (such as MATLAB-SIMULINK), and ever increasing capabilities of engineering workstations. A comprehensive, transient model of the multi-cylinder engine is linked with models of the torque converter, transmission, transfer case and differentials. The engine model is based on linking the appropriate number of single-cylinder modules, with the latter being thermodynamic models of the in-cylinder processes with built-in physical sub-models and transient capabilities to ensure high fidelity predictions. Either point mass or multi-body vehicle dynamics models can be coupled with the powertrain module to produce the ground vehicle simulation.

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.

A two phase, global combustion model has been developed for quiescent chamber, direct injection diesel engines. The first stage of the model is essentially a spark ignition engine flame spread model which has been adapted to account for fuel injection effects. During this stage of the combustion process, ignition and subsequent flame spread/heat release are confined to a mixing layer which has formed on the injected jet periphery during the ignition delay period. Fuel consumption rate is dictated by mixing layer dynamics, laminar flame speed, large scale turbulence intensity, and local jet penetration rate. The second stage of the model is also a time scale approach which is explicitly controlled by the global mixing rate. Fuel-air preparation occurs on a large-scale level throughout this phase of the combustion process with each mixed fuel parcel eventually burning at a characteristic time scale as dictated by the global mixing rate.

A long-distance microscope with pulse-laser as optical shutter up to 25kHz was used to magnify the diesel spray at the nozzle hole vicinity onto 35-mm photographic film through a still or a high-speed drum camera. The injectors examined are high-pressure valve-covered-orifice (VCO) nozzles, from unit injector and common rail injection systems. For comparison, a mini-sac injector from a hydraulic unit injector is also investigated. A phase-Doppler particle analyzer (PDPA) system with an external digital clock was also used to measure the droplet size, velocity and time of arrival relative to the start of the injection event. The visualization results provide very interesting and dynamic information on spray structure, showing spray angle variations, primary breakup processes, and spray asymmetry not observed using conventional macroscopic visualization techniques.

High unburned hydrocarbon emissions and poor fuel consumption arise in a carburetted two-stroke engine because of its scavenging process. Time resolved hydrocarbon concentration at the exhaust port has shown a definite trend in concentration of unburned hydrocarbon with respect to crank angle. This paper discusses an exhaust gas recirculation system designed to trap fraction of the exhaust gas that is rich in short circuited fresh charge. In this design, the differential pressure between the crankcase and the exit at the exhaust port is communicated with each other at the appropriate time through passages in the piston and the cylinder block. The design is thus capable of selectively trapping and recirculating fraction of the exhaust gas rich in short circuited fresh charge back into the cylinder for combustion.