Добірка наукової літератури з теми "621.43.06:621.436"

Turbocharging systems are of high importance in the enhancement of engine power and efficiency. Faults in such systems may cause increased emissions levels beyond those set by legislation, and may also compromise fuel efficiency. This thesis investigates the application of system identification and vibration signal analysis techniques for the performance monitoring of turbocharged diesel engines by exploring turbocharger behaviour. The first technique is based on the use of system identification to build models representing the input and output relationship of an engine process. In this case, torque demand is the input, and the turbocharger speed is the output in a medium duty, turbocharged diesel engine. The proposition set here is that the model that can be derived does not have to reflect the complexity of the physical system. Hence, if simple models can be derived, any deviation from the model of normal operation, if adhering to some principles, could indicate the existence of a fault in a system. Dynamic linear auto-regressive moving averages with exogenous input (ARMAX) models were estimated to represent the relationship between input and output. The models have been used to demonstrate the capability of the proposed technique to diagnose faults.

This thesis describes the development of high efficiency turbochargers and turbogenerators to significantly increase the power to weight ratio and reduce both the fuel consumption and emissions from heavy duty diesel engines. A literature overview is provided for turbomachinery based exhaust energy recovery projects in the public domain. The technologies are discussed in detail and compared using real test data. The thesis describes some design issues that were experienced during engine testing one with a heat shield and one with a volute - and how finite element analysis was used to generate solutions and long term evolutions in the designs. A variable nozzle guide vane ring was designed but seizing of the mechanism occurred during testing. A low friction coating was shown to be the solution.

The main focus of this thesis is the investigation of nonlinear control designs on the airpath of a diesel engine equipped with exhaust gas recirculation (EGR) and variable geometry turbocharger (VGT). This problem presents strong couplings between controlled variables and actuators, since both EGR and VGT flows are driven by gases in the exhaust manifold. An additional coupling arises from the common shaft of the compressor and the turbine. The multivariable, highly nonlinear dynamics of the system gives motivation for model-based nonlinear control. Firstly, an eighth order mean-value model of the diesel engine is derived. This is consequently used to perform closed-loop simulations and to tune the controller gains offline. To reduce the complexity of the controllers, a third-order mean-value is used to design the nonlinear controllers.

The work contained in this thesis presents a computational study on the effects of fuel stream perturbations in non-premixed flames in terms of pollutant formation (soot and NOx), including the application to a practical case scenario, such as direct injection diesel engine. The initial part of the work concentrates on the implementation in FLUENT of a soot model that is based on the Eddy Dissipation concept of Magnussen, which accounts for the effects of small scale turbulence in the formation and depletion of soot particles.

The term 'dual fuel' refers to a compression ignition engine where a small quantity of diesel fuel called the pilot is used to ignite a second gaseous fuel which is the primary energy source. The motivation to use dual fuel has traditionally been economic, as the primary fuel is often less expensive than the distillate fuel it replaces. However, some benefits in terms of the reduced emissions of smoke and oxides of nitrogen (NOx) can also be achieved. In this research, a small, direct injection diesel engine was converted to dual fuel operation. This engine is typical of those used in stationary power generation applications. A review of literature revealed that whilst performance and emissions trends were well established for indirect injection engines, little research had been conducted on a direct injection engine. In particular, this class of small, high speed industrial engine had been somewhat neglected, partly because they have been subject to less stringent emissions legislation than their automotive counterparts. By performing a detailed investigation ' into the errors and assumptions that have a bearing on the three zone technique, it was possible to challenge some previous assumptions regarding the dual fuel combustion process. Namely, the theory that the pilot bums in two separate initial stages was found to be a deficiency of previous analysis techniques and therefore incorrect. It was found that as the proportion of the gaseous fuel was increased, the combustion process retained similar characteristics and magnitudes of mass burned to diesel until all but the highest equivalence ratios. At this point, the premixed and diffusion burning periods merged, but continued to show a fundamental dependence on the pilot ignition and the combustion processes were never independent of the pilot. The range of equivalence ratios over which the transition between the two patterns occurs is firstly a function of the primary fuel, and secondly a function of the operating conditions (such as in cylinder temperature). It is proposed that the dual fuel combustion process is better described as a diesel combustion process with a modified diffusion burning period that results from the gaseous fuel concentration and type. By using this explanation, it was identified that the emissions characteristics of the engine could be modified through the use of a second fuel. The primary fuel can reduce the initial mass burning rates (to reduce NOx) and simultaneously elevated the diffusion burning rates (to reduce smoke emissions). This provides an alternative, beneficial means by which the classic diesel NOx-Particulate trade-off can be manipulated. Butane was found to be unsuitable for this type of engine, and propane consistently yielded the best performance and emissions trends. Additionally, it was found that the addition of small quantities of methane or propane can result in disproportionately large reductions in smoke and NOx without the penalty of increased carbon monoxide and unburned hydrocarbons.