Higher Mean Effective Pressure Research Articles

Influence of initial electric arc root position on electric arc behavior with spark plugs in large lean burn spark ignited gas engines

Increasing efficiency while reducing emissions leads to high mean effective pressures, high compression ratios and increasingly lean operation for spark ignited large gas engines. Despite these boundary conditions, gas engines must be operated between knocking and misfiring at low cycle-to-cycle fluctuations. The excess air ratio and the ignition process of the lean mixture greatly influence the stability of the combustion process. To enable sufficiently low cycle-to-cycle fluctuation of the combustion process despite the ever increasing excess air ratio levels, it is necessary to understand and investigate the sub-areas of the engine process, for example, ignition, flow condition and mixture formation. This paper focuses on one sub-area of conventional spark ignition, the influence of the electric arc root position on the origin and stretching of the electric arc, because electric arc behavior is considered important in the subsequent combustion process. The results show that electric arc roots on the downstream end of the electrodes tend to enable a longer electric arc length at the first electric arc short circuit (i.e. the first abrupt shortening of the electric arc during its spark duration) than electric arcs with electric arc roots on the upstream ends of the electrodes.

Valved Heat Engine Working on Modified Atkinson Cycle

There is immense scope for the development of heat engines that can directly convert solar and biochemical renewable sources of thermal energy to high-grade energy. Regenerative Stirling cycle heat engine with its performance criteria of highest thermal efficiency and high mean effective pressure is theoretically the best engine for small capacity reciprocating heat engine. However, the practical Stirling engine performance is far from the ideal. As an alternative, practical heat engines based on thermodynamic cycles (without regeneration) other than the Stirling cycle have been suggested. This paper deals with a new concept in the design of reciprocating heat engine working on modified Atkinson cycle. In the Atkinson cycle, expansion ratio being higher than compression ratio, the thermal efficiency is better than that of the standard Otto cycle. Heat engine design based on the suggested modified Atkinson cycle can be an alternative to the practical Stirling engine. In the conceptual mechanical design of the engine suggested here, apart from utilizing the principle of Atkinson cycle for achieving higher thermal efficiency, the mechanical configuration of the reciprocating engine ensures a high degree of inertial force balancing. This can result in reduced vibrations in the mountings of the power units.

Assessment of a rotary compressor performance operating at transcritical carbon dioxide cycles

The unique features of the CO 2 transcritical cycle of high mean effective pressure, high pressure differential and low pressure ratio have significant impact on the design of the compressor. This paper assesses the performance of a rolling piston compressor when operating at a transcritical CO 2 cycle. The compressor performance in terms of refrigerant flow rate, leakage mass flow, friction loss, compressor torque and valve performance are discussed and shown. Among others, the results suggested that for a given compressor capacity, it is better to have a compressor with a shorter cylinder operating at a higher compressor speed than vice versa.

A study of the improvement effect of Miller-cycle on mean effective pressure limit for high-pressure supercharged gasoline engines

A theoretical adiabatic combustion cycle model of the Miller-cycle was made in order to study its effect on increasing mean effective pressure. The model can evaluate the maximum cylinder pressure, exhaust gas temperature and knocking tendency, which cause reliability problems in high-pressure supercharged gasoline engines. The theoretical calculations with this model and experiments with an actual engine show good coincidence and indicate the advantage of the Miller-cycle, such as higher mean effective pressure, than the Otto-cycle with lower nominal compression ratio while maintaining the same reliability conditions.

Some Aspects of Constant Pressure Turbocharged Marine Diesel Engines of Medium and Low Speed

The constant pressure turbocharge system is widely used in marine diesel engines because of its high thermal efficiency. This study has been made to establish a simulation system for exhaust gas pulsation of the constant pressure turbocharge system and to clarify its characteristics. The previous paper reported that the pressure fluctuations measured on test units and some engines agreed very well with those simulated by the scheme developed in this study. The study used the characteristic method for solving the differential equations of unsteady flow. This report will first discuss the high thermal efficiency of this turbocharge system in the range of high mean effective pressure, then it will show the advantages of the two-step Lax-Wendroff’s method in solving the unsteady flow equations in comparison with the characteristic method. Furthermore, it will present some characteristics of the pulsation and the unique pulsation resonance in this turbocharge system.

Characteristics of Exhaust Gas Pulsation of Constant Pressure Turbo-Charged Diesel Engines

The constant pressure turbo-charge system has now been increasingly adopted for marine diesel engines because of its higher thermal efficiency in the range of higher mean effective pressure. However, it seems that there has been no paper published on the exhaust gas pulsation of this sytem. In this study, a gas flow model of the constant pressure turbo-charged diesel engines was assumed as a basic and fundamental one, and an investigation was made of it. As a result, some characteristics of the exhaust gas pulsation of this system have been clarified and a mathematical simulation system has been established. It must be emphasized that the filling and emptying method which neglects wave propagation cannot simulate the pulsation, although it can simulate the average exhaust gas pressure and temperature of this system.

Investigation of Diesel Engine and Turbocharger Interaction

The authors are concerned with the proper provisioning of turbochargers and fuel-injection equipment for diesel engines, particularly in the automotive class. Medium-speed engines are run at high mean effective pressures and there is a tendency towards similar outputs in automotive engines. Because of transmission demands these outputs will be required over a wide speed range and the relation of engine air and fuel requirements is examined. The simple turbocharger is not ideally suited to wide range matching and the extent of the compromise inherent in fixed geometry compressors and turbines is discussed. In order to survey engine, turbocharger, and fuel-system interactions tests are reported where turbocharger limitations are avoided by the use of two units in series. Engine operating limits were selected on the basis of safe engine factors and the output assessed with respect to the principal variables of turbocharger pressure ratio and engine compression ratio. The resulting compromise between high cylinder pressures and smoke control tended towards a traction-type torque curve with a higher-than-conventional fall-off in torque with speed. A suggestion was verified that smoke occurred at higher air/fuel ratios as the charge density increased. Nevertheless accepted methods of heat-release prediction from rate of injection characteristics were not affected by variation in charge density.

Diesel Engines at High Mean Effective Pressures and Their use in Ships

Diesel Engines at High Mean Effective Pressures and Their use in Ships

A Theoretical Investigation into the Porting of a Two-Cycle High Mean Effective Pressure Internal Combustion Engine

The paper is an attempt to determine on paper the sizes of ports and their timing to attain a high mean effective pressure—that is, a mean effective pressure of the order of 200 lb. per sq. in. as is usual in present day high-duty four-cycle engines—in a two-cycle engine of the half-stroke sleeve type. In the course of this attempt the various unknown factors influencing the accuracy of the results are pointed out and comments are made about these factors.