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In the present paper a new method is proposed for the analysis of the two main phases of the engine exhaust stroke blowdown and displacement. The method is based on the processing of fast-response experimental temperatures obtained from the exhaust manifold wall during the engine cycle. A novel experimental installation has been developed, which separates the engine transient temperature signals into two groups, namely the long- and the short- term response ones. This has been achieved by processing the respective signals acquired from two independent data acquisition systems. Furthermore, a new pre-amplification unit for fast response thermocouples, appropriate heat flux sensors and an innovative, object-oriented, control code for fast data acquisition have been designed and applied. For the experimental procedure a direct injection (DI), air-cooled diesel engine is used.

Simulation tools are currently extensively used to assist diesel engine development because they contribute to significant reduction of development cost and time. Given that currently the majority of DI diesel engines are turbocharged it is of vital importance the knowledge of Turbine and Compressor maps for successful prediction of engine performance. This data is often not available from T/C manufacturers, especially for the turbine. However, even if turbine maps are available, efficiency and mass flow characteristics span over a limited range of pressure ratio, due to limitations of conventional T/C test benches. Use of sophisticated T/C test bench equipment that allows measurements at a wider range of T/C pressure ratios results in increased hardware and labour cost. An alternative solution is the development of physically based models for the turbine and the compressor.

A theoretical study is conducted to examine the effects of oxygen enrichment of intake air and exhaust gas recirculation (EGR) on heavy-duty (HD) diesel engine performance characteristics and pollutant emissions. A phenomenological multi-zone model was properly modified and used to assess the impact of intake air oxygen-enhancement and EGR on the operating and environmental behavior of a HD diesel engine under various operating conditions. Initially, an experimental validation was performed to assess the predictive ability of the multi-zone model using existing data from a HD turbocharged common-rail diesel engine at the 12 operating points of the European Stationary Cycle (ESC) considering certain high-pressure cooled EGR rate at each operating point.

Cylinder pressure measurements are common practice for internal combustion reciprocating engines during field or lab applications for the purpose of combustion analysis, condition monitoring etc. The most accurate method is to measure cylinder pressure using a crank angle encoder as a trigger source to guarantee cylinder pressure measurement at predefined crank angle events. This solution, even though favorable, presents a number of practical difficulties for field applications and increased cost, for this reason its use is practically restricted to lab applications. Therefore a commonly used approach for ad hoc measurements is to digitize samples at fixed time intervals and then convert time into crank angle assuming a constant rotational speed. But if engine rotational speed is not constant within the engine cycle this may result to incorrect cylinder pressure CA referencing.

The present paper deals with the development and evaluation of a new semi-empirical, pseudo-multi-zone model capable of estimating NOx emissions for various types of diesel engines and also different engine configurations. The specific model is physically based due to the use of the first thermodynamic law and the consideration of combustion chemistry and dissociation of the combustion products during the closed part of the engine cycle. The model estimates the fuel burning rate through Heat Release Rate Analysis of the measured cylinder pressure which is then coupled to a simplified multi-zone approach, assuming that each element of fuel burns individually at controlled conditions having from this point on its own history inside the combustion chamber. From this procedure, a simplified multi-zone semi-empirical model is developed, that accounts for the temperature distribution inside the combustion chamber and its evolution during an engine operating cycle.

High efficiency, power concentration and reliability are the main requirements from Diesel Engines that are used in most technical applications. This becomes more important with the increase of engine size. For this reason the aforementioned characteristics are of significant priority for both marine and power generation applications. To guarantee efficient engine operation and maximum power output, both research and commercial communities are increasingly interested in methods used for supervision, fault-detection and fault diagnosis of large scale Diesel Engines. Most of these methods make use of the measured cylinder pressure to estimate various critical operating parameters such as, brake power, fuel consumption, compression status, etc. The results obtained from the application of any diagnostic technique, used to assess the current engine operating condition and identify the real cause of the malfunction or fault, depend strongly on the quality of these data.

Further reduction of brake specific fuel consumption (bsfc) in heavy-duty diesel engines, which are used for vehicle applications, is of utmost importance due to high fuel prices, global warming issue (CO₂ emissions) and continuously stringent environmental regulations. Specifically, the necessity for further reduction of specific diesel oil consumption and increase of vehicle mileage, respectively, is more pronounced in large haul diesel trucks due to technical, environmental and economical reasons. Heavy-duty (HD) direction injection (DI) diesel engines are used in these vehicles, which indicate a rather high power output in the range of 200-400 kW. During recent years, various measures have been proposed from engine manufacturers and researchers for improving combustion process and through that, increasing the fuel economy of diesel engines.

The past decade significant research effort has concentrated on the DI diesel engine due to stringent future emission legislation which requires drastic reduction of engine tail pipe pollutant emissions, mainly PM and NOx, without significant deterioration of specific fuel consumption. Towards this effort, the important role of modeling to investigate and understand the impact of various internal measures on combustion and emissions has been widely recognized. Phenomenological models can significantly contribute towards this direction because they have acceptable prediction capability and the advantage of low computational time. This enables the production of results, on a cycle basis, that indicate the effect of various parameters on both engine performance and emissions. Therefore their use can significantly reduce engine development time (i.e. reduction of experimental effort) and cost.

In the present work is presented a detailed evaluation of an advanced diagnostic technique, developed by the authors, for the determination of diesel engine condition and tuning. For this purpose, an extended experimental investigation has been conducted on a prototype test engine installed in the author's laboratory. During the measurements various operating parameters (i.e. torque, fuel consumption, injection pressure, cylinder pressure, peripheral temperatures etc.) have been recorded at various operating conditions (i.e. engine speed and loads). Initially the engine operated at its normal conditions (i.e. reference state). Then, two “virtual” faults (i.e. reduction of injector opening pressure and increase of cylinder mass leakage) were introduced, that affected engine operation.

A difficulty which exists when applying diagnostic techniques on large-scale diesel engines operating on the field, is that usually it is not possible to obtain measurement data at a wide engine operating range due to a number of constraints. In the present work is investigated the possibility to overcome this practical difficulty originating from the test procedure for engines operating on the field (i.e. marine or stationary applications). The main objective is to examine if a diagnosis procedure provides similar results when applied at various engine operating conditions. For this purpose an existing diagnostic technique, developed by the authors, is applied at different operating conditions on a large-scale two-stroke diesel engine used for power generation in a Greek island.

In this paper, the results are presented from the analysis of the second stage of an experimental investigation with the aim to provide insight to the cyclic, instantaneous heat transfer phenomena occurring in both the cylinder head and exhaust manifold wall surfaces of a direct injection (DI), air-cooled diesel engine. Results from the first stage of the investigation concerning steady-state engine operation have already been presented by the authors in this series. In this second stage, the mechanism of cyclic heat transfer was investigated during engine transient events, viz. after a sudden change in engine speed and/or load, both for the combustion chamber and exhaust manifold surfaces. The modified experimental installation allowed both long- and short-term signal types to be recorded on a common time reference base during the transient event.

During recent years, the deterioration of greenhouse phenomenon, in conjunction with the continuous increase of worldwide fleet of vehicles and crude oil prices, raised heightened concerns over both the improvement of vehicle mileage and the reduction of pollutant emissions. Diesel engines have the highest fuel economy and thus, highest CO2 reduction potential among all other thermal propulsion engines due to their superior thermal efficiency. However, particulate matter (PM) and nitrogen oxides (NOx) emissions from diesel engines are comparatively higher than those emitted from modern gasoline engines. Therefore, reduction of diesel emitted pollutants and especially, PM and NOx without increase of specific fuel consumption or let alone improvement of diesel fuel economy is a difficult problem, which requires immediate and drastic actions to be taken.

An experimental analysis is carried out to investigate several heat transfer characteristics during the engine cycle, in the combustion chamber and exhaust manifold walls of a direct injection (DI), air-cooled, diesel engine. For this purpose, a novel experimental installation has been developed, which separates the engine transient temperature signals into two groups, namely the long-and the short- term response ones, processing the respective signals in two independent data acquisition systems. Furthermore, a new pre-amplification unit for fast response thermocouples, appropriate heat flux sensors and an innovative, object-oriented, control code for fast data acquisition have been designed and applied. Experimentally obtained cylinder pressure diagrams together with semi-empirical equations for instantaneous heat transfer were used as basis for the calculation of overall heat transfer coefficient.

A major challenge for researchers and engineers in the field of diesel engine development is the simultaneous reduction of both NOx and soot emissions from diesel engines to comply with strict future emission legislation. One of the promising internal measures that focus on the reduction of soot emissions is post fuel injection which does not have a serious effect on NOx emissions. The main parameters involved when using this technique are post fuel quantity and dwell angle between the main and the post fuel injection events. In the present work a detailed computational investigation has been conducted to determine the effect of post fuel injection on engine performance and pollutant emissions (NOx and soot). To this scope, a phenomenological multi-zone combustion model has been used, properly modified to take into account the interaction of post and main injected fuel amounts.

The compression ignition engine of the dual fuel type has been employed in a wide range of applications utilizing various gaseous fuel resources, while minimizing soot and nitric oxide emissions without excessive increase in cost against that of the conventional direct injection diesel engine. Fumigated dual fuel compression ignition engines are divided into two main groups: the conventional dual fuel engines where part of the liquid fuel is replaced by gaseous one and the pilot ignited ones where a pilot amount of the liquid fuel is used as an ignition source. Due to the high auto-ignition temperature of the natural gas, it can be used as a supplement for the liquid diesel fuel in conventional diesel engines operating under dual fuel mode. Moreover, the use of natural gas as a supplement for the liquid diesel fuel could be a solution towards the efforts of an economical and clean burning operation.

Despite the improvement in HD Diesel engine out emissions future emission legislation requires significant reduction of both NOx and particulate matter. To accomplish this task various solutions exist involving both internal and external measures. As widely recognized, it will be possibly required to employ both types of measures to meet future emission limits. Towards this direction, it is necessary to reduce NOx further using internal measures. Several solutions exist in that area, but the most feasible ones according to the present status of technical knowledge are EGR, water injection or fuel/water emulsions. These technologies aim to the reduction of both the gas temperature and oxygen concentration inside the combustion chamber that strongly affect NOx formation. However, there remain open points mainly concerning the effectiveness of water addition techniques and penalties related to bsfc and soot emissions.

Considering future emission legislation for HD diesel engines it is apparent that it will be probably necessary to employ A/T devices to achieve them. The main problem concerns the simultaneous control of both NOx and particulate emissions at an acceptable fuel penalty. Concerning particulate matter the use of particulate traps is considered to be a proven technology while for NOx emission control; various solutions exist mainly being the use of SCR catalysts or LNT devices. But LNT traps require periodical regeneration, which is accomplished by generating reducing agents i.e. CO and H2. The present investigation focuses on the regeneration of LNT devices through the engine operating cycle. This can be achieved using two techniques, additional injection of fuel at the exhaust manifold (external measures) or operation at low lambda values in the range of 1.0 or lower (internal measures).

Considering future emission legislation and the global thermal problem, two are the main issues that are of specific concern for the future of the diesel engine, specific gaseous pollutants and CO2 emissions. Both parameters are related to engine bsfc consumption directly or indirectly. The last is becoming even more important considering current fuel prices and the projection for the future indicating a trend for increasing fuel prices. The last decade significant improvement have been accomplished in the field of diesel engine efficiency that has resulted to considerable reduction of engine bsfc. It is obvious that despite improvements in diesel engine efficiency still a considerable amount of energy is rejected to the environment through the exhaust gas. Approximately 30-40% of the energy supplied by the fuel is rejected to the ambience.

In the present work a sensitivity analysis is conducted using a multi-zone phenomenological model developed in the past by the author's, to estimate the effect of model's constants on engine performance and emissions. The constants used for this analysis are those embedded in the semi-empirical relations of the model, regarding air entrainment rate, combustion rate, ignition delay and evaporation rate. The model is applied on a heavy duty supercharged DI diesel engine and the effect of each of these constants on measurable engine parameters is defined. From the sensitivity analysis the relation between model constants and engine output data is derived. These results are used to define a constants determination procedure. The target is to define a limited number of adjustable constants so that the procedure can be of practical use. Following this, the calibration procedure is applied to determine the value of each constant, at various engine speeds and loads for the engine in question.

During the last years a great effort has been made by many NATO nations to move towards the use of one military fuel for all the land-based military aircraft, vehicles and equipment employed on the military arena. This idea is known to as the Single Fuel Concept (SFC). The fuel selected for the idea of SFC is the JP-8 (F-34) military aviation fuel which is based upon the civil jet fuel F-35 (Jet A-1) with the inclusion of military additives possessing anti-icing and lubricating properties. An extended experimental investigation has been conducted in the laboratory of Thermodynamic and Propulsion Systems at the Hellenic Air Force Academy. This investigation was conducted with the collaboration of the respective laboratories of National Technical University of Athens and Hellenic Naval Academy as well.