Diesel engines can be 2 stroke or 4 stroke in design. The difference in the diesel comes in its ignition system. It uses compression ignition to ignite a burn in the combustion chamber. The efficiency of a diesel is generally better due to the high compression ratios used. Large diesels are generally of 2 stroke configuration for simplicity. Most road vehicles use the 4 stroke configuration.
The catalytic converter “cat” for short was developed back when carburetor was still being used on production vehicles. They were made to clean up hc or hydrocarbon emissions (unburnt gas) They do so by means of a catalytic reaction, meaning the hc’s chemically change to something not harmful. Catalytic converters have progressed through the years. At one time they had an air tube running to them, because the have to stay close to a correct air to fuel ratio. They would regulate air to control the reaction so that the catalyst would not overheat and burn up. Cats also need some heat to work properly, and do not do well at startup. This is why some manufacturers have had to add pre-cats that heat up quickly so that they pass manufacturer emission requirements. catalytic converters can sometimes malfunction and cause the engine to run poorly and not have much power. Usually if your driving up the interstate and pull over to look under the car it will be glowing if the cat is plugged up. Unfortunately the only true test is to remove it and look inside of the converter. The converters either have beads in them or normally have honeycomb layers. If damaged pieces will probably be turned sideways or fall out when you remove them. Many times you can replace your converter for cheaper, if you use an aftermarket high flow converter. The high flow catalitic converter will probably give you better fuel economy and power due to less restriction. High flow catalitic converters are also safe to pass emission tests if you are required to do so.
Fuel injection has become popular due to the emission restrictions made by the epa. The fuel can be controlled much more precisely, due to all the information presented by the sensors to the ecu. There are different types of fuel injection systems. The first progression was to a throttle body setup. The system was simple and had the advantages of precise control. Unfortunately this system has alot of short comings, being that the fuel was being put in the engine in the same location as the carb. The problem with this is that the fuel “puddles” or drops out of suspension and collects on the intake manifold walls. As the engine demands more power (air) the extra airflow pulls the puddled fuel into the cylinders. When the engine stays at a constant speed the ratio moves from lean to rich inconsistantly. Another problem with this setup is that the fuel still travels through the manifold. Intake manifolds are inconsistent and often flow different amounts of air into different cylinders. This leads to cylinders changing from rich to lean.
Carburetors or carbs for short, have been a way of controlling fueling of engines from the beginning and are still used today in racing such as nascar. The simplicity and ease of tuning is still a favorite of many racing sanctions that dont want to worry about traction control and various other forms of trickery from being hidden inside fuel control boxes. Carbs work off the venturi affect, while the engine is running it is moving air out of the exhaust. On the intake side the engine developes a vacuum. As the air rushes in the carb the diameter of the air opening gets smaller in the middle of the carb. The fuel outlets will be located at the smallest diameter called the venturi. The air coming in the engine must accelerate as it passes through the venturi, trying to fill the vacuum in the intake manifold. The venturi is where the fuel will expel, due to the vacuum being created by the acceleration of the air. The jets, which control the fuel flow are located upstream of the outlets. Most carbs have a low rpm circuit and a high rpm jets called pilot or idle jets and main jets. Like everything in an engine if the carb flows more air it has the ability to make a huge difference in power. Some stock carbs such as carter, webber and quadrajet were a little more complex due to the car manufacturer having to have precise fuel control for emissions compliance. Most racing sanctions such as nascar and nhra use holly carbs for their simplistic nature to tune.
EGR stands for exhaust gas recirculation. It was one of the first methods deployed to fight high nox values. The valve allows a controlled amount of exhaust to be sent back into the intake of the engine. The exhaust has a high content of carbon dioxide and inhibits the peak combustion pressure thus reducing nox. By using this method car manufacturers are allowed to use higher compression ratios. The recirculation occurs in the lower to mid rpm range. The recirculation stops the enging from knocking (detonating) at part throttle, high load conditions. The egr isn’t used or very little at idle. The combustion pressures are not very high due to low engine speed. Also at a little less than full throttle the egr disengages. By disengaging it allows the combustion pressures to raise and make more power. The engine will not detonate at full throttle, unlike part throttle conditions the fuel ratio will be very rich at or close to full throttle to make power.
The 2 stroke engine has always had a problem with hydrocarbon (unburnt gas) emissions. The amount of overlap, the time when the intake and exhaust are both open, can not be controlled as well as a 4 stroke can with it’s valves. This is the same problem that has plagued the rotary engine until recently, when a new port configuration was used on them. Unfortunately another problem with two strokes is that most people want to build them up and make more horsepower. Normally a tuned exhaust is one of the first modifications done, due to a large increase in power for a reasonable amount of money. The purpose of an expansion chamber is to reflect a pressure wave back to the cylinder. If timed correctly in a certain rpm range, this strong pulse will be reflected away from the cylinder which creates a vacuum at the cylinder. The overlap period takes atvantage of this situation as the fresh intake air rushes into the cylinder. As the air fuel mixture fills the cylinder it does a great job of increasing the volume which translates to power.
Disp.——-Layout——Perf. HP/rpm——Torque Lb.ft/rpm