Their only disadvantage is their low efficiency at part loads due to losses by throttling the air. Spark-ignition engines can run very smoothly and at low noise level and are therefore expecially suitable for passenger cars. d = Acceptable range to be maintained by closed-loop control of air–fuel mixture via λ control. λ < 1, excess of fuel λ = 1, stoichiometric mixture λ > 1, excess of air.Λ = stoichiometric / The left side is measured before the catalyst the right side is measured after the catalyst. Because a mixture ratio close to stoichiometry must be provided within the cylinder under all air conditions (temperature, pressure), output control can be achieved only by altering air density, which is done by throttling the intake air. For petrol (and for diesel fuel as well), this is ∼14.5 kg of air per kilogram fuel (λ = 1). The ignition of the fuel mixture by an electric spark is possible only when conditions are close to being stoichiometrically correct, that is, only when the quantity of oxygen in the air is correct for complete oxidation of the hydrocarbons. The spark-ignition engine works with a mixture of air and atomized fuel produced by fuel injection into the induction pipe (widely used), by fuel injection into the combustion chamber (increasing in application), or in the carburetor (classical method, rarely used today). The knock resistance of a fuel depends on the composition of the hydrocarbon mixture and additives, some of which act as knock inhibiters (lead, tetraethyl, and tetramethyl). ![]() High octane numbers approaching 100 are sought. ![]() The thermal efficiency depends mainly on the compression ratio ɛ, which is limited by the knock tendency (i.e., tendency toward spontaneous ignition of the fuel, which is characterized by the octane number). 20A) is the universal engine for all fuels of low inflammability, especially gasoline (a mixture of several hydrocarbons), but also liquefied petroleum gas (LPG), liquefied natural gas (LNG), methanol and ethanol (alcohols), and hydrogen. Hans Joachim Förster, Hermann Gaus, in Encyclopedia of Physical Science and Technology (Third Edition), 2003 IV.C.1 Spark-Ignition Engine ![]() Through the results obtained it was intended to establish whether 60% is a practical limit for the approach or whether there would be benefit in further downsizing, and that such a downsized engine could in itself provide a route to a 35% reduction in vehicle tailpipe CO 2 (importantly, without the use of hybridization other than a Stop/Start system). Consequently the Ultraboost project was formed with the major tasks of specifying, designing, building and operating an engine with a minimum of 60% downsizing factor. To date production downsized engines have generally been configured with a DF in the region of approximately 40%, with one research engine shown with this value at 50%. There are significant synergies with other commonplace technologies such as direct injection (DI) and camshaft phasing devices, too. ![]() This is normally done by pressure charging the engine, with turbocharging generally being favoured because it allows some exhaust gas energy recovery. These savings can help to offset the additive technologies required to recover the power output, because some means of increasing specific output has to be provided to retain installed power in a vehicle. Thermal losses also improve and, in the case of downsizing and ‘decylindering’ from a Vee-configuration engine to an in-line one, crevice volume losses can be markedly reduced and there are potentially significant bill of materials (BOM) and manufacturing cost savings, too. Where η mech is the mechanical efficiency, p ¯ brake is the brake mean effective pressure (BMEP) and p ¯ ind is the gross indicated mean effective pressure (IMEP). At the same time, the mechanical efficiency increases, this being defined as The advantages of downsizing a 4-stroke spark-ignition (SI) engine stem chiefly from shifting the operating points used in the engine map for any given flywheel torque, so that the throttle is wider-open to the benefit of reduced pumping losses. To the OEM the attractions of a downsizing strategy include that gasoline engine technology is very cost-effective to produce versus diesel engines (especially when the costs of the exhaust after treatment (EAT) system are included), that there are still significant efficiency gains to be made due to the losses associated with the 4-stroke Otto cycle, and that pursuing the technology does not entail investing in completely new production facilities (as would be required by a quantum shift to electric or fuel-cell vehicles, for example). Where DF is the downsizing factor, V Swep t NA is the swept volume of a naturally-aspirated engine of a given power output and V Swep t Downsized is the swept volume of a similarly-powerful downsized alternative. Eqn 1 DF = V Swep t NA − V Swep t Downsized V Swep t NA ,
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