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Classical Engine Design Calculations Using Spreadsheets. A.C.Erskine, R.Ali, G.G.Lucas, A.Hughes. Classical methods of design and analysis of engine components are in danger of fragmentation and falling into disuse because of their ad hoc development and lack of continuity of personnel. It is argued that although advanced and comprehensive numerical methods of analysis have recently become available to engine designers, classical techniques still have a useful role to play in the design office. To retain their continual use and to enhance it, it is necessary to translate and integrate the existing classical techniques into user friendly computer software. This has been achieved in a software package, CEDS, discussed in this paper. The software is quick and easy to use allowing rapid parametric studies in the early stages of design of components.

Computerisation of Classical Engine Design Techniques using Spreadsheets. A.C.Erskine, R.Ali, G.G.Lucas, A.Hughes. Traditionally, engine components have been analysed using models with sufficient simplification to enable solutions to be calculated by hand. With the increasing availability of powerful computers these ‘classical’ techniques are being forgotten in favour of more accurate, but more complex and time consuming, finite element methods. This paper discusses the benefits of using classical analysis techniques and describes a user-friendly, spreadsheet based system for their application. The Classical Engine Design System (CEDS) is quick and simple to use making parametric studies in the early design stages easy. These can be used to evaluate the feasibility of a design in order to justify time and money spend on further, more detailed analysis. Microsoft's Excel spreadsheet package, running on a P.C., has been used as a basis for the software.

The use of the throttle valve in the intake of the spark ignition engine is one reason for the lower part load efficiency of this engine when compared with the compression ignition engine. The need for the throttle valve can be avoided by the disablement of individual cylinders. A microprocessor is being used to operate on the fuel injection to the inlet ports as a means to disable the cylinders. It is being programmed such that the cylinders disabled, cycle by cycle, can be varied in order to keep all the cylinders hot and to minimise the amplititude of the vibrations of the power unit on its mountings. Further, the number of cylinders disabled, cycle by cycle, can be varied in order to provide a fine control of engine power output. The control system is described and the results of the experimental test work are presented.

An electronically controlled fuel system has been developed which enables the injection timing and fuel delivery to be adjusted from engine cycle to cycle using a small micro-computer and a solenoid operated injector. The injector uses a powerful solenoid to control the needle lift of a standard injector and employs pressure time metering to regulate the fuel delivery. The microcomputer is used to determine the required timing pulses which are used to control the current in the solenoid. The maximum delivery of the injector is 60mm3/injection and the system has been successfully tested on an 1800 cc IDI four cylinder engine fitted with Pintaux fuel injectors.

Measurements have been made of the rate of flame propagation, the cylinder pressure and the combustion rate for twenty one spark ignition engine combustion chamber designs. These show that, for a given compression ratio, the flame speed is not significantly affected by chamber design. However, the rate of combustion, the pressure history and cyclic dispersion are greatly affected. A computer simulation has been developed which uses a simple but effective integration technique to determine the combustion chamber geometric parameters. This, too, shows that combustion chamber design has a marked effect on combustion rate and that the effect is due to the degree of compactness of the chamber. The paper includes also work on spark plug position and dual spark plugs.

This paper describes the performance and emissions of a spark-ignited engine using a dual-Fuel mixture of petrol and a small flow rate of hydrogen. Such an engine can be run at all speeds with a wide-open throttle and the specific fuel consumption and B.T.E. figures indicate a greater part load efficiency than those from a throttled engine. Similar results are also presented using a higher compression ratio of 11.7:1. Emissions data indicate reduced levels of CO, CO2, and NOx at part load due to the very lean mixtures used. No problem of backfiring has been experienced since the concentration of hydrogen is very low. Work is continuing on the storage of the hydrogen in a suitable hydride and on a mechanism to introduce the hydrogen directly into the engine cylinder, rather than into the intake system.

Tests on a single-cylinder engine have shown that the flame speed and lean extinction limir may be increased by the fitment of a “vortex generator” in the engine intake. This consists of a nest of delta wings which generates a vortex system in the inlet air flow. The results show that this vortex generator should be of variable geometry and replace the conventional throttle. The main instrumentation on the engine consists of a flame logger which accepts amplified signals from ionisation probes set in the engine combustion chamber. The logger is gated to count those flames which travel across the combustion chamber during a set crank angle period. Information from this instrumentation is presented in the form of graphs describing the effect of vortex generator blockage ratio, mixture strength, engine speed, load and spark timing upon the percentage number of flames which cross the chamber and apparent flame speed.

Emissions of nitric oxide and hydrocarbons are affected by various parameters, combustion duration interval being one of them that can alter the levels of nitric oxide in the exhaust. To some extent hydrocarbon emission depends upon the temperature particularly near the walls. Changes in combustion duration interval alters pressure history in the chamber by changing maximum pressure, rate of pressure rise and the time required for the maximum pressure to occur. This study looks at the relative effects of this on the nitric oxide formation and investigates the hydrocarbon emission when the flame initiation point is changed.

The development of a hot wire anemometry system to study the turbulent flow conditions in spark ignition engine combustion chambers is described. Measurements of a ‘mean’ flow velocity and a fluctuating flow velocity within certain frequency bandpass ranges are reported under ‘motoring’ engine conditions during the ‘combustion period’ of the engine cycle. Two types of combustion chamber design have been investigated - a ‘squish’ design and a cylindrical disc design.

The highest concentrations of NO appear in the exhaust of a spark ignition engine when it is operated slightly on the lean side of stoichiometry. A suggested method of control therefore is to run the engine at an off-stoichiometric air/fuel ratio where the nitric oxide emission is low. Operating the engine in the fuel rich region entails high emissions of carbon monoxide and unburned hydrocarbons and is not compatible with the idea of conserving fuel energy. Therefore, it is advisable to run the engine in the lean mixture region. A number of models have been developed in the past to predict NO emission levels by the use of the rate kinetic reactions: In these the oxygen atom concentration has been assumed to be that at equilibrium and this has been justified on the basis that the rate of heat release is greater than the rate of NO formation.

The temperature history at a location in the combustion chamber of a spark ignition (SI) engine is determined by using the intensity of radiation from the recombination continuum CO + O ↠ CO2 + hv. The flame was initiated separately at two locations in the combustion chamber while the radiation was monitored at one location thereby making the arrangement somewhat equivalent to monitoring the radiation from two different gas zones in the chamber. Agreement between the predicted temperature history with heat transfer and the experimental temperature measurements was found to be good around the stoichiometric region but large differences were noticed when the engine was run at lean mixture strengths.

The formation of nitric oxide in the combustion chamber of a spark ignition engine is formulated by developing a simple model. The state of the gas in the chamber and its thermal properties are estimated during a complete cycle. The estimation of the nitric oxide formation is based on the Zeldovich mechanism and assumes the burned gas either in a fully mixed or unmixed state. A simple heat transfer relation is used to estimate the heat loss from the gas to the chamber walls. The effect of the position of the ignition source relative to the exhaust port is also taken into account, and the predicted nitric oxide concentrations are compared with experimental results from a single-cylinder variable compression ratio IFP engine. It is found that the nitric oxide concentration predicted by the model agrees well over most of the operating range with the experimentally measured nitric oxide concentrations in the exhaust gas.

The mathematical model of the compression, combustion, and expansion phases of the Renault IFP variable compression ratio research engine reported here is an attempt to combine as many as possible of the basic characteristics of engine combustion. Finite rates of flame propagation and heat release are computed on the basis of Semenov's theory. To allow for the effects of turbulence, Semenov's estimate of laminar burning velocity is multiplied by a term derived from flame speed measurements in the engine. Dissociation of the burned gases is compensated by chemical equilibrium and heat transfer data due to Annand. The computer model makes possible a parametric study of the effects of variables such as mixture composition, spark timing, compression ratio, engine speed, exhaust residuals and injected water as a means of controlling certain obnoxious emissions resulting from use of propane, isooctane, and benzene fuels. Experimental data corroborate the accuracy of the model.