Search Results

In general most engine models for control applications have been constructed using regressions fitting and measured engine data. Such techniques have also been used to model the dynamic performance of engines. Unfortunately regression equation models are very complex and do not show directly the physical reality from which they emerge. This has for example made it impossible to write down explicitly the dymanic equations for, for example, the air exchange process in an SI engine in any form other than as the manifold pressure state equation. In recent a publication a Mean Value Engine Model (MVEM) has been constructed for an SI engine which is physically based and which has a simple physical form which can be immediately understood and manipulated.

One of the most important operating modes for SI engines is in the idle speed region. This is because SI engines spend a large part of their time operating in this mode. Moreover, a large measure of operator satisfaction is dependent on an engine operating smoothly and reliably in and around idle. In particular the operator expects that the idle speed will remain constant in spite of the engine loads due to power steering pumps and air conditioning compressors. In the idle speed region an SI engine is thought to be quite nonlinear because the engine loading can be quite significant, thus forcing the engine to be driven through a reasonably large portion of its lower operating range. Many of the earlier studies of idle speed control systems have dealt with linearized models which in principle have limited validity for the problem at hand. In order to improve this situation, it is necessary to deal with the more general nonlinear control problem.

Experimental investigations have been conducted with two identical small scale SI gas engines gen-sets operating on biomass producer gas from thermal gasification of wood. The engines where operated with two different compression ratios, one with the original compression ratio for natural gas operation 9.5:1, and the second with a compression ratio of 18.5:1. It was shown that high compression ratio SI engine operation was possible when operating on biomass producer gas from a TwoStage gasifier. The results showed an increase in the electrical efficiency from 31% to 35% when the compression ratio was increased. The influence of ignition timing on emissions was investigated during high compression ratio operation. It was shown that for λ=1.4 the NOx emission decreases by almost a factor 3, when the timing is retarded from 13° to 7° before top dead center.

Of late there has been a resurgence in studies investigating parameters that quantify combustion knock in both standardized platforms and modern spark-ignition engines. However, it is still unclear how metrics such as knock (octane) rating, knock onset, and knock intensity are related and how fuels behave according to these metrics across a range of conditions. As part of an ongoing study, the air supply system of a standard Cooperative Fuel Research (CFR) F1/F2 engine was modified to allow mild levels of intake air boosting while staying true to its intended purpose of being the standard device for American Society for Testing and Materials (ASTM)-specified knock rating or octane number tests. For instance, the carburation system and intake air heating manifold are not altered, but the engine was equipped with cylinder pressure transducers to enable both logging of the standard knockmeter readout and state-of-the-art indicated data.

Mean Value Engine Models (MVEMs) are simplified, dynamic engine models which are physically based. Such models are useful for control studies, for engine control system analysis and for model based engine control systems. Very few published MVEMs have included the effects of Exhaust Gas Recirculation (EGR). The purpose of this paper is to present a modified MVEM which includes EGR in a physical way. It has been tested using newly developed, very fast manifold pressure, manifold temperature, port and EGR mass flow sensors. Reasonable agreement has been obtained on an experiemental engine, mounted on a dynamometer.

An important paradigm for the modelling of naturally aspirated (NA) spark ignition (SI) engines for control purposes is the Mean Value Engine Model (MVEM). Such models have a time resolution which is just sufficient to capture the main details of the dynamic performance of NA SI engines but not the cycle-by-cycle behavior. In principle such models are also physically based, are very compact in a mathematical sense but nevertheless can have reasonable prediction accuracy. Presently no MVEMs have been constructed for intercooled turbocharged SI engines because their complexity confounds the simple physical understanding and description of such engines. This paper presents a newly constructed MVEM for a turbocharged SI engine which contains the details of the compressor and turbine characteristics in a compact way. The model has been tested against the responses of an experimental engine and has reasonable accuracy for realistic operating scenarios.

Mean Value Engine Models (MVEMs) are dynamic models which describe dynamic engine variable (or state) responses as mean rather than instantaneous values on time scales slightly longer than an engine event. Such engine variables are the independent variables in nonlinear differential (or state) equations which can be quite compact but nevertheless quite accurate. One of the most important of the differential equations for a spark ignition (SI) engine is the intake manifold filling (often manifold pressure) state equation. This equation is commonly used to estimate the air mass flow to an SI engine during fast throttle angle transients to insure proper engine fueling. The purpose of this paper is to derive a modified manifold pressure state equation which is simpler and more physical than those currently found in the literature. This new formulation makes it easier to calibrate a MVEM for different engines and provides new insights into dynamic SI engine operation.

With the tightening of exhaust emission standards, wide bandwidth control of the air/fuel ratio (AFR) of spark ignition engines has attracted increased interest recently. Unfortunately, time delays associated with engine operation (mainly injection delays and transport delays from intake to exhaust) impose serious limitations to the achievable control bandwidth. With a proper choice of sensors and actuators, these limitations can be minimized provided the port air mass flow can be accurately predicted ahead in time. While the main objective of this work is to propose a complete AFR controller, the main focus is on the problems associated with port air mass flow prediction.

The liquefied natural gas (LNG)-fueled ships were provisioned to meet the strict emission legislation in the marine application since 2000. However, the scientific approach of burning the low-emission natural gas in lean combustion uncovered that the engine suffers from high methane slip emission. Serious questions are raised about the quantity of methane slip during marine conditions when the load varies in multiple frequencies and amplitudes. Previous studies by these authors explained how methane slip increases during load oscillation. This paper examined several practical methods to reach stable combustion in transient conditions to reduce the methane slip. Employing Proportional-Integral-Derivative (PID) controllers in a closed loop, implementing open-loop lookup tables, model predictive controller (MPC), and an innovated solenoid method are performed in a high-fidelity medium-speed natural gas spark-ignition (SI) engine model.

Mean value engine models (MVEMs) seek to predict dynamically the mean values of important SI engine variables such as the crank shaft speed, the manifold pressure and the theoretical air/fuel ratio (lambda). Previous work also shows that such models can be made quite accurate, both for stationary and transient operating modes. Because these models can be made mathematically simple and compact, they are also tractable for direct mathematical and physical analysis. In this paper an analysis of a mean value engine model is carried out which reveals the underlying structure of the problems which face engine control system designers. In particular it is shown that an SI engine is extremely nonlinear and time dependent. Because of this, conventional control strategies using conventional sensors cannot be made to operate correctly in the transient regime. An “ideal” nonlinear compensator is also described for the fueling dynamics which works over a wide operating range.

Long term stoichiometric Air/Fuel Ratio (AFR) control of an SI engine is at the present mainly maintained by table mapping of the engine's fresh air intake as a function of the engine operating point. In order to reduce a stationary error in the AFR to zero the table based control normally works in conjunction with a PI feedback from a HEGO sensor. The effective bandwidth of this feedback loop is quite small and seldom exceeds 2 Hz. This is altogether too small for accurate transient AFR control. This paper presents a new λ (normalized Air/Fuel Ratio) control methodology (H∞ control) which has a somewhat larger bandwidth and can guarantee robustness with respect to selected engine variable and parameter variations.

Long term control of the AFR (Air/Fuel Ratio) of spark ignition engines is currently accomplished with a selvoscillating PI control loop. Because of the intake/exhaust time delay, the oscillation frequency and hence bandwidth of this loop is small. This paper describes a new approach to the design of this control loop using a novel observer system. In this way the bandwidth of this important loop is increased by a factor of 2 - 6 times, leading to more accurate overall AFR control. Moreover the observer approach is so robust and allows such feedback levels that it reduces significantly the accuracy required in the calibration of the base fuel control system with which it is be used. It can be used with either conventional- or advanced observer based- base fuel strategies.