 | This article relies largely or entirely on a single source .(May 2024) |
In engine technology, a reverse-flow or non-crossflow cylinder head is one that locates the intake and exhaust ports on the same side of the engine. The gases can be thought to enter the cylinder head and then change direction to exit the head. This is in contrast to the crossflow cylinder head design.
The main advantage of the reverse-flow cylinder head is that both the entering inlet charge and the exiting exhaust gas cause a tendency to swirl in the same direction in the combustion chamber. [1] In a crossflow head the inlet and exhaust gases promote swirl in opposite directions so that during overlap the swirl changes directions. The constant swirl during overlap which results in a reverse-flow cylinder head promotes better mixing, hence better scavenging of the end gas. The fact that the inlet charge must change direction before exiting the exhaust makes it less likely that fresh mixture will exit the exhaust before mixing during overlap. Overall this improves volumetric efficiency and reduces emissions.
In carbureted engines, poorly atomized fuel reduces efficiency and power at lower rpm (at higher rpm the large air speed keeps the mixture in suspension). The inlet manifold of a reverse-flow cylinder head may be connected to the exhaust by a heat riser to transfer further heat, improving low rpm response and emissions as a result.
Costs can be reduced in production engines by casting the inlet and exhaust manifolds as one unit. This also transfers further heat to the inlet eliminating the need for manifold heating and other related devices. Such an engine is overall simpler, and has improved cold starting.
The reverse flow design is generally considered[ according to whom? ] to be inferior to a crossflow design in terms of ultimate engineering potential for two reasons. Firstly, there is limited space when inlet and exhaust ports are arranged in a line on one side of the head meaning a reduction in port area compared to a crossflow head. This mainly affects power delivery at high rpm by limiting airflow. Secondly, since inlet and exhaust manifolds are both on the same side of the engine and in close proximity, the inlet manifold and carburetor (if applicable) are heated by the exhaust. This heating reduces the density of the inlet charge and hence the volumetric efficiency of the engine. In a spark-ignition petrol engine the heat also increases the likelihood of pre-ignition or detonation which limits the allowable compression ratio reducing both power and efficiency.[ citation needed ]
Engineering has found a number of solutions to the first problem such as staggering the ports by placing the inlet ports on a higher level than the exhausts. This way larger ports can be used while still leaving enough room for flanges and fasteners. This brings with it the problem that the exhaust ports have a tighter turn radius. This problem is somewhat offset by the larger port. Another popular solution, as used in the BMC A-Series and Holden 6-cylinder engines is the siamesed port. In this configuration one large port feeds 2 adjacent cylinders. The gain in area comes from effectively removing the material between 2 adjacent ports. This solution encourages charge robbing, where one cylinder "robs" the charge from the port leaving the next one with less mixture. This happens because the 2 cylinders which share the port are not equally spaced in terms of firing order. For example, the Leyland Mini with its 1-3-4-2 firing order has the 1 and 2 inlets siamesed and the 3 and 4 inlets siamesed. First the number 3 sucks the mixture out of the port, then there is less left for number 4. While number 1 and 2 are sucking the port again fills with mixture and the process repeats leaving the number 1 and 4 cylinders always lacking mixture. Also the siamese port can make both acoustic and inertial ram air tuning less effective due to the irregular pulse. One should keep in mind that larger ports are only necessary at higher rpm and that small ports are desirable at low rpm to improve air speed. Due to charge robbing and lower air speeds, large siamesed ports are more suited to high rpm race motors.
The heat problem can be minimized by staggering the ports in terms of height and using heat proof wraps and coatings on the exhaust header to the point that it poses a negligible problem. The heat can also be used as an advantage.
When forced induction is used, large port flow is not as important as it is when an engine is naturally aspirated. This means that the generally inferior flow of a reverse-flow head is less of a disadvantage. In the early days of turbo charging a reverse-flow head allowed the compressor outlet of a turbocharger to blow directly into the inlet manifold with either a blow-through or draw-through carburettor and no intercooler. This allowed the use of shorter inlet plumbing which decreased turbo lag and lowered flow restriction. Modern turbocharged configurations utilizing intercoolers and fuel injection are more difficult to plumb up to a reverse-flow head and are ideally suited to a cross flow head where the turbo is on the exhaust side of the engine, the charge crosses through an intercooler in front of the engine and into the inlet manifold on the other side.
The reverse flow head was ideally suited to a production carbureted engine due to its low rpm performance and ease of manufacture. The design could be modified for high performance by porting (in particular siamese) and isolating the inlet manifold from the exhaust header. The configuration is also perfect for carbureted non-intercooled turbo-charging. However, the advent of fuel injection and electronic ignition has made most of the reverse-flow head's advantages redundant in a modern engine and as a result the design has lost its popularity. The reverse-flow head still enjoys some popularity among enthusiasts including Leyland Mini, Chrysler Slant-6, Holden and Ford Inline 6 fans. In fact some Australian Ford enthusiasts consider the 250 2V reverse-flow head to be superior to the Honda designed[ citation needed ] cross-flow head that replaced it.
In an internal combustion engine, a turbocharger is a forced induction device that is powered by the flow of exhaust gases. It uses this energy to compress the intake air, forcing more air into the engine in order to produce more power for a given displacement.
In engineering, the Miller cycle is a thermodynamic cycle used in a type of internal combustion engine. The Miller cycle was patented by Ralph Miller, an American engineer, U.S. patent 2,817,322 dated Dec 24, 1957. The engine may be two- or four-stroke and may be run on diesel fuel, gases, or dual fuel. It uses a supercharger or a turbocharger to offset the performance loss of the Atkinson cycle.
A two-strokeengine is a type of internal combustion engine that completes a power cycle with two strokes of the piston in one revolution of the crankshaft. In a two-stroke engine, the end of the combustion stroke and the beginning of the compression stroke happen simultaneously, with the intake and exhaust functions occurring at the same time.
A stratified charge engine describes a certain type of internal combustion engine, usually spark ignition (SI) engine that can be used in trucks, automobiles, portable and stationary equipment. The term "stratified charge" refers to the working fluids and fuel vapors entering the cylinder. Usually the fuel is injected into the cylinder or enters as a fuel rich vapor where a spark or other means are used to initiate ignition where the fuel rich zone interacts with the air to promote complete combustion. A stratified charge can allow for slightly higher compression ratios without "knock," and leaner air/fuel ratio than in conventional internal combustion engines.
A four-strokeengine is an internal combustion (IC) engine in which the piston completes four separate strokes while turning the crankshaft. A stroke refers to the full travel of the piston along the cylinder, in either direction. The four separate strokes are termed:
In a piston engine, the cylinder head sits above the cylinders, forming the roof of the combustion chamber. In sidevalve engines the head is a simple plate of metal containing the spark plugs and possibly heat dissipation fins. In more modern overhead valve and overhead camshaft engines, the head is a more complicated metal block that also contains the inlet and exhaust passages, and often coolant passages, Valvetrain components, and fuel injectors.
Engine tuning is the adjustment or modification of the internal combustion engine or Engine Control Unit (ECU) to yield optimal performance and increase the engine's power output, economy, or durability. These goals may be mutually exclusive; an engine may be de-tuned with respect to output power in exchange for better economy or longer engine life due to lessened stress on engine components.
A crossflow cylinder head is a cylinder head that features the intake and exhaust ports on opposite sides. The gases can be thought to flow across the head. This is in contrast to reverse-flow cylinder head designs that have the ports on the same side.
The GM Ecotec engine, also known by its codename L850, is a family of all-aluminium inline-four engines, displacing between 1.2 and 2.5 litres. Confusingly, the Ecotec name was also applied to both the Buick V6 Engine when used in Holden Vehicles, as well as the final DOHC derivatives of the previous GM Family II engine; the architecture was substantially re-engineered for this new Ecotec application produced since 2000. This engine family replaced the GM Family II engine, the GM 122 engine, the Saab H engine, and the Quad 4 engine. It is manufactured in multiple locations, to include Spring Hill Manufacturing, in Spring Hill, Tennessee, with engine blocks and cylinder heads cast at Saginaw Metal Casting Operations in Saginaw, Michigan.
In automotive engineering, an exhaust manifold collects the exhaust gases from multiple cylinders into one pipe. The word manifold comes from the Old English word manigfeald and refers to the folding together of multiple inputs and outputs.
An inlet manifold or intake manifold is the part of an internal combustion engine that supplies the fuel/air mixture to the cylinders. The word manifold comes from the Old English word manigfeald and refers to the multiplying of one (pipe) into many.
The Toyota JZ engine family is a series of inline-6 automobile engines produced by Toyota. As a replacement for the M-series inline-6 engines, the JZ engines were 24-valve DOHC engines in 2.5- and 3.0-litre versions.
Lean-burn refers to the burning of fuel with an excess of air in an internal combustion engine. In lean-burn engines the air–fuel ratio may be as lean as 65:1. The air / fuel ratio needed to stoichiometrically combust gasoline, by contrast, is 14.64:1. The excess of air in a lean-burn engine emits far less hydrocarbons. High air–fuel ratios can also be used to reduce losses caused by other engine power management systems such as throttling losses.
Alfa Romeo Twin Spark (TS) technology was used for the first time in the Alfa Romeo Grand Prix car in 1914. In the early 1960s it was used in their race cars (GTA, TZ) to enable it to achieve a higher power output from its engines. And in the early and middle 1980s, Alfa Romeo incorporated this technology into their road cars to enhance their performance and to comply with stricter emission controls.
The anti-lag system (ALS) is a method of reducing turbo lag or effective compression used on turbocharged engines to minimize turbo lag on racing or performance cars. It works by retarding the ignition timing and adding extra fuel to balance an inherent loss in combustion efficiency with increased pressure at the charging side of the turbo. This is achieved as an excess amount of fuel/air mixture escapes through the exhaust valves and combusts in the hot exhaust manifold spooling the turbocharger creating higher usable pressure.
The Honda F-Series engine was considered Honda's "big block" SOHC inline four, though lower production DOHC versions of the F-series were built. It features a solid iron or aluminum open deck cast iron sleeved block and aluminum/magnesium cylinder head.
In an internal combustion engine, twin-turbo is a layout in which two turbochargers are used to compress the intake fuel/air mixture. The most common layout features two identical or mirrored turbochargers in parallel, each processing half of a V engine's produced exhaust through independent piping. The two turbochargers can either be matching or different sizes.
Barra is a name for an engine range created by Ford Australia, including the inline-6 and unrelated SOHC V8 in the Ford Australia Falcon between 2002 and 2016. The inline-6 engines are unique to the Australian manufactured Falcon and Territory and were developed and manufactured in Geelong, Victoria. The Barra was first introduced in the BA Falcon, named after the "Barramundi" code name used during the development of the BA update engine. The V8 engine, from Windsor, Ontario, were discontinued with the FG model whereas the I6 engines continued production until 26 September 2016, coinciding with the end of production of the Falcon and Territory on 7 October.
A carbureted compression ignition model engine, popularly known as a model diesel engine, is a simple compression ignition engine made for model propulsion, usually model aircraft but also model boats. These are quite similar to the typical glow-plug engine that runs on a mixture of methanol-based fuels with a hot wire filament to provide ignition. Despite their name, their use of compression ignition, and the use of a kerosene fuel that is similar to diesel, model diesels share very little with full-size diesel engines.
An internal combustion engine is a heat engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal combustion engine, the expansion of the high-temperature and high-pressure gases produced by combustion applies direct force to some component of the engine. The force is typically applied to pistons, turbine blades, a rotor, or a nozzle. This force moves the component over a distance. This process transforms chemical energy into kinetic energy which is used to propel, move or power whatever the engine is attached to.