What are the main methods of fuel deliver in an SI engine Wh

What are the main methods of fuel deliver}\' in an SI engine? What method is used in most modern automobiles? Why? ANS. Why is an engine with port injection vs. carburetion more likely to have fuel dilute the lubricating oil? ANS. Why did some aircraft engines in World War II have water injection? What is the physical phenomenon? ANS. What is the difference between multipoint port injection systems and a common rail system? ANS.

Solution

Qno1. The main method of delivery in an SI engine

Modern fuel delivery systems are designed depending on the type of fuel used and the performance required by the automobile. A fuel delivery system also ensures the cleanliness of the fuel. Electronic injection system are more popular now a days. The main difference between electronic injection and mechanical injection is that an electronic system is controlled by a complex microprocessor control unit (sometimes called an electronic control unit or ECU), which is basically a miniature computer. This computer is fed with information from sensors mounted on the engine. These measure factors such as the air pressure and temperature in the air intake, the engine temperature, accelerator position and engine speed. All this information allows an electronic system to meter the fuel far more accurately than the simple mechanical system, which relies on sensing the airflow alone.The modern fuel delivery system uses Fuel pump relays. It produces adequate volume and pressure is the bottom line for fuel pump performance. A fuel pump relay is an electric switch that is directed on or off by the power train control module (PCM). When the ignition key is turned on initially for a period of three seconds in order to pressurize the system, and the next time the key goes to start, the PCM helps to activate the fuel pump relay again. Once the engine starts, the PCM gets signals from the crankshaft sensors to either turn off the pump or keep it running. Modern vehicles have an inertia switch to turn off the pump in the event of any accident. Anti-theft devices helps to deactivate the fuel pump in case if it detects tampering. Modern filters and regulators, pulse modulated fuel pumps, fuel system diagnostic are some important features of the modern fuel delivery system.

Qno2:

Fuel dilution is one of the phenomena occur more readily in port injection engines than engine having carburetor. The factors contributing to oil dilution are fuel properties and oil/cooling water temperatures in multipoint-injection engines. Gasoline like fuel has lower viscosity and lower boiling point. In addition to these factors, fuel injection timing is another factor that increases fuel dilution in direct-injection engines. Fuel may impinge on and adhere to the cylinder liner wall sometime that also cerate lube oil dilution. While in case of carburetion we generally use fuel air mixture and the fuel sticking to cylinder liner is low.

Qno3

Detonation, in any engine, should always be avoided by either lowering inlet temperatures, using higher octane fuel, retarding ignition, hence lowering engine output, lowering engine blow-by (a situation in which high crankcase pressure sends oil fumes back inside the combustion chamber), running the engine a little richer than at the stoechiometric ratio, lowering the compression ratio and/or boost pressure,Water injection is used to lower in-cylinder temperatures and burn the air/fuel mixture more efficiently thus helping avoid detonation. For gaining higher compression ratio without knocking water injection was used

Qno4

CRDi consists of a common rail which holds fuel at a very high pressure (~1400 bar) and injects diesel directly into the cylinder during the transition from compression stroke to power stroke. Due to the high pressure injection, the fuel burns efficiently and hence power and fuel efficiency figures are improved.

MPFI on the other hand is simply multi point fuel injection. Here, the carburetor is replaced with a MAP sensor and injection points in the intake manifold. the MAP sensor relays to the ECU as to the amount of air entering the manifold and accordingly the quantity of fuel to be injected into the cylinder heads is ascertained (to maintain the best possible air-fuel mixture as per the requirements).