1 Modeling and control of fuel to air ratio in an internal combustion engine with unknown evaporation time and fuel fraction impinging manifold's wall Ali I. Hassan 1 , Hayder J.Kurji 2 , Najah F. Jasim 3 Mechanical Engineering Department, College of Engineering, University of Karbala. Abstract: In this paper we develop a model for fuel to air ratio (FAR) in internal combustion engine (I.C.E). Based on this model, we can represent the FAR in terms of the fuel injected to the manifold, evaporation time, and the part of fuel that impinges the wall. This model is derived in this paper from other models existing in the literature in (I.C.E). The importance of this proposed model is represented in providing a controllable dynamics that allows us to design a control law for achieving a desired FAR in spite of unknown evaporation time and injected fuel fraction impinging the wall. This usefulness of the model is demonstrated in this paper throughout designing a control law to make the FAR tracks a desired value using Routh-Herwitze criterion. Both of the proposed model and control law are proved mathematically. Moreover, a numerical simulation is performed and shows the validity of the proposed model and designed controller. Nomenclature FAR Fuel-to-Air Ratio Time constant of fuel film evaporation (s). ff  n Fraction of injected fuel. ff m Mass of intake fuel film(kg). . ) kg/s ( Mass flow rate a, b Negative and positive constants respectively 1 Introduction In the last decade, increasing attention has been devoted to the study of transient phenomena related to the operation and the design of Engine Control Systems (ECS) to design suitable compensation strategies for mixture strength excursions and to assure good conversion levels for pollutant gases in catalytic converters. In order to accomplish exhaust regulations, an accurate control of Air fuel ratio has to be guaranteed both in steady state and transient conditions, estimating correctly the air mass flow at the injector location and injecting the fuel in the right amount and with the appropriate time dependence. This goal can be reached making use of engine control strategies based on both online measurements and dynamic model estimations. Many engine dynamic models have been described 1 omer2006a@yahoo.com 2 heyder_gurji@yahoo.com 3 jasimn2@asme.org