Athanasios M. Dimaratos

Experimental Assessment of Turbocharged Diesel Engine Transient Emissions during Acceleration, Load Change and Starting

The control of transient emissions from turbocharged diesel engines remains an important objective to manufacturers, since newly produced engines must meet the stringent criteria concerning exhaust emissions levels as dictated by the legislated Transient Cycles. In the present work, experimental tests are conducted on a medium-duty, turbocharged and after-cooled diesel engine in order to investigate the behavior and formation mechanism of nitric oxide (NO), smoke and combustion noise emissions under various transient operating schedules including acceleration, load change and starting. To this aim, a fully instrumented test bed was set up in order to record and research key engine and turbocharger variables during the transient events. The main parameters measured are nitric oxide concentration and smoke opacity (both using ultra-fast response analyzers) as well as combustion noise. Various other variables were monitored, such as in-cylinder pressure, engine speed, fuel pump rack position, boost pressure and turbocharger speed. The main focus of the experimental investigation was devoted to engine acceleration tests representative of automotive and truck applications, commencing from various engine speeds and loads. The experimental test pattern also included load increases and (cold and hot) startings. Analytical diagrams are provided to explain the behavior of exhaust emissions development in conjunction with turbocharger and governor/fuel pump response. Turbocharger lag was found to be the main cause for the emissions peak values observed during all transient events. During starting, the lack of air and its mismatch with fueling caused excessive black smoke, identified by the extremely high values of exhaust gas opacity.

Combustion noise radiation during the acceleration of a turbocharged diesel engine operating with biodiesel or n-butanol diesel fuel blends

In the current study, experimental tests were conducted on a turbocharged truck diesel engine in order to investigate the mechanism of combustion noise radiation during various accelerations and for various fuel blends. With this aim, a fully instrumented test bed was set up in order to capture the development of key engine and turbocharger parameters. Apart from the baseline diesel fuel, the engine was operated with a blend of diesel with either 30 vol % biodiesel or 25 vol % n-butanol. Analytical diagrams are provided to explain the behaviour of combustion noise radiation in conjunction with the cylinder pressure, the pressure rise rates, the frequency spectrum and the turbocharger and governor–fuel pump responses. The blend of diesel fuel with n-butanol exhibited the highest noise emissions throughout each of the transient tests examined, with differences up to 4 dBA from those with neat diesel operation. On the other hand, the biodiesel blend was found to behave marginally noisier than neat diesel oil but without a clear trend established throughout the transient events.

Evaluation of Various Dynamic Issues During Transient Operation of Turbocharged Diesel Engine with Special Reference to Friction Development

The modeling of transient turbocharged diesel engine operation appeared in the early seventies and continues to be in the focal point of research, due to the importance of transient response in the everyday operating conditions of engines. The majority of research has focused so far on issues concerning thermodynamic modeling, as these directly affect heat release predictions and consequently performance and pollutants emissions. On the other hand, issues concerning the dynamics of transient operation are often disregarded or over-simplified, possibly for the sake of speeding up program execution time. In the present work, an experimentally validated transient diesel engine simulation code is used to study and evaluate the importance of such dynamic issues. First of all, the development of various forces (piston, connecting rod, crank and main crankshaft bearings) is computed and illustrated in order to evaluate the importance of abrupt load increases on the bearings durability. The usual approximation of the connecting rod being considered as equivalent to two masses (one reciprocating with the piston and the other rotating with the crank) is put into test. The same holds true for another usual assumption, i.e. the crankshaft being considered as sufficiently rigid. In this work, the engine crankshaft is analyzed in detail with the instantaneous torsional angle between engine and load taken into account. Thus, details are provided concerning the development of crankshaft torsional deformation during transients. The main part of the paper focuses on the development and contribution of various friction components during turbocharged diesel engine transients. This is accomplished via the use of a recently proposed detailed friction model. Mean fmep (friction mean effective pressure) modeling is found to considerably underestimate actual friction around firing TDC, leading to lower speed droops for abrupt load increases. The piston rings assembly contribution is dominant for the particular engine, due to its high number of piston rings and its relatively low crankshaft speed. The model can be used to investigate such interesting cases as the effect of engine oil temperature

Experimental Study of Transient Nitric Oxide, Smoke, and Combustion Noise Emissions during Acceleration of an Automotive Turbocharged Diesel Engine

The control of transient emissions from turbocharged diesel engines is an important objective for automotive manufacturers, since newly produced engines must meet the stringent criteria concerning exhaust emissions levels as dictated by the legislated Transient Cycles Certification. In the current study, experimental tests are conducted on an automotive, turbocharged diesel engine in order to investigate the formation mechanism of nitric oxide, smoke, and combustion noise emissions under various acceleration schedules experienced during daily driving conditions. To this aim, a fully instrumented test bed was set up in order to capture the development of key engine and turbocharger variables during the transient events. Analytical diagrams are provided to explain the behaviour of emissions development in conjunction with turbocharger and governor/fuel pump response. Turbocharger lag was found to be the main cause for the emission spikes during all test cases examined, with the engine calibration playing a vital role. The analysis was extended with a quasi-steady approximation of transient emissions using steady-state maps, in order to highlight the effect of dynamic engine operation on pollutants and combustion noise emissions.

Study of crankshaft torsional deformation under steady-state and transient operation of turbocharged diesel engines

The modelling of transient operation of turbocharged diesel engines appeared in the early 1970s, and continues to be in the focal point of research due to the importance of transient response in the everyday operating conditions of engines. The majority of studies have focused so far on thermodynamics, as this directly affects heat release predictions and consequently performance and pollutants emissions. On the other hand, issues concerning the dynamics of engine operation are often disregarded or over-simplified. In the present work, an experimentally validated diesel engine simulation code is used to study and evaluate the importance of a notable engine dynamic issue, i.e. the crankshaft torsional (angular) deformations during turbocharged diesel engine operation owing to the difference between instantaneous engine and load (resistance) torques. The analysis aims ultimately in studying the phenomena under the very demanding, and often critical, transient operating conditions. Detailed crankshaft angular momentum equilibrium is formulated that takes into account instantaneous gas, inertia, friction, load as well as stiffness, and damping torque contributions. Details are provided concerning the underlying mechanism of the crankshaft torsional deformations during steady-state and transient operation. This deformation can assume significant values depending on the engine-load configuration (load change, crankshaft stiffness, kind of aspiration of the engine), and as such it is of great importance for safe engine operation.

Exhaust emissions estimation during transient turbocharged diesel engine operation using a two-zone combustion model

A comprehensive, two-zone, transient, diesel combustion model is used to study the performance and exhaust emissions of a turbocharged diesel engine during load transients. Analytical modelling of fuel spray and in-cylinder processes is included, while detailed equations concerning all engine sub-systems describe the phenomena, which diversify transient operation from the steady-state. Demonstrative diagrams are provided for the time histories of nitric oxide (NO) and soot emissions during transient operation, and the main factors affecting their formation are highlighted. Moreover, in-cylinder development of NO concentration and soot density during individual transient cycles is provided and compared with their respective steady-state counterparts. This comparison points out the differences between steady-state and transient operation, as regards exhaust emissions development. The study is expanded with the investigation of load change magnitude and cylinder wall insulation effects on transient emissions.

Investigation of turbocharged diesel engine operation, exhaust emissions, and combustion noise radiation during starting under cold, warm, and hot conditions

Control of performance and transient emissions from turbocharged diesel engines is an important objective for automotive manufacturers, since stringent criteria for exhaust emissions must be met. In particular, (cold) starting is of exceptional importance owing to its significant contribution to the overall emissions during a transient test cycle. In the present work, experimental tests were conducted on a turbocharged and after-cooled bus–truck diesel engine in order to investigate the engine operating behaviour and the formation mechanisms of nitric oxide, smoke, and combustion noise during cold, warm, and hot starting. With this as a target, a fully instrumented test bed was set up, using ultra-fast response analysers capable of capturing the instantaneous development of emissions and various key engine and turbocharger parameters. The experimental test pattern included a variety of starting conditions, defined by the thermal status of the engine (i.e. the coolant temperature) and its idling speed. As expected, turbocharger lag was found to be the major contributor for the pollutant emissions spikes in all cases, with the thermal status of the engine and its idling speed playing important roles in the combustion (in)stability, turbocharger response, and noise radiation.

Development of combustion instability and noise during starting of a truck turbocharged diesel engine

In the current study, experimental tests were conducted on a truck turbocharged diesel engine to investigate the mechanisms of combustion noise radiation and combustion instability during various starting schedules experienced in daily driving conditions, namely under cold and hot operations. To this aim, a fully instrumented test bed was set up to capture the development of key engine and turbocharger properties. Analytical diagrams are provided to explain the behaviour of combustion instability and noise radiation in conjunction with all relevant parameters, such as cylinder pressure and pressure spectrum, turbocharger and governor/fuel pump response.