Inputs and Outputs of an Engine Management Systems - Assignment Example

Engine Management Systems Name Date Instructor Course Name Inputs (sensors) and outputs of an Engine Management System (EMS) for a spark ignition petrol engine with turbocharger Sensors help cut down fuel consumption and harmful emissions in an engine. They play an important role in boosting the engine efficiency. Sensors function to capture and transmit data about the engine operations. The input sensors include the following: Engine airflow sensor This sensor measures the amount of airflow entering the engine. The engine airflow sensor is important in reducing the carbon (IV) oxide emissions by ensuring the optimum air to fuel ratio. This promotes complete combustion and therefore reduces the CO2 emissions. They also supply information on temperature, humidity and intake air volume. It contains a small computer that calculates the internal current flow. This helps the EMS to adjust the injector pulse width and spark ignition timing (Stone, et, al., 2004) Baro sensor/Manifold absolute pressure sensor (MAP) The pressure sensor measures the air pressure in the intake manifold to determine the air intake. It provides important information which helps the EMS to calculate the amount of fuel to be injected. This promotes the correct air fuel mix and therefore promotes good combustion and reduces emissions. It works by detecting the vacuum pressure created and sends the information to the EMS which adjusts the fuel injections (Andrew, 2014.) The oxygen sensor It analyzes the exhaust fumes to determine the oxygen content so as to ensure that the engine is using the correct amount of fuel. The ideal air fuel ratio maintained by the EMS is 14.7 parts of air to 1 part of fuel. The oxygen sensors are made of materials that detect oxygen content and produce a voltage; the engine coolant temperature sensor detects and communicates the temperature of the vehicle. This controls the action of the radiator fan. If the temperature are too high, the fan rotates quickly and if low slowly (Uk.vdo 2014). Air temperature sensor The Intake Air Temperature sensor (IAT) tells the EMS the temperature of the incoming air. It is usually locate in the air filter. It helps control the overall temperature of the car and performance; the cooler the engine the higher the performance. Knock sensor It is a piezoelectric device that generates some voltage when exposed to vibration. Sensor signal varies in amplitude depending on the intensity of knock. The signals help the EMS to retard the ignition timing to compensate for the knocking which protects the pistons against damage. Throttle position sensor It tells the EMS that the acceleration pedal is being stepped on. The EMS therefore increases the injector pulse width and spark ignition timing. This is after confirming with the MAP. Camshaft position sensor It is electromagnetic in nature. It produces a voltage when a metal passes near it. It therefore communicates to the EMS about the position of the camshaft. The information helps the EMS to calculate the open valve and therefore eject fuel into it. Crankshaft sensor It helps to know the position of the crankshaft and the rotations per minute. This helps to know which injector needs to be activated. It should be synchronized with the camshaft sensor for better engine performance. Actuators include the idle air controller This keeps the rotations per minute of the engine steady. It does not supply information to the EMS but works under the command of it making it an output. It increases the rotations per minute until the temperature of the engine is per the manufacturers specifications in regards to temperature. Throttle valves: they regulate the mixture of air and fuel by increasing or decreasing the volume of incoming air (Obdii, 2014).The EMS also regulates the charging system voltage: cycles the cooling fan on and off, interacts with the anti-lock brake system to reduce power and the automatic temperature control to modulate the temperatures. Methods used by an EMS to calculate spark advance and fuel injection quantity. Fuel injection is a system of delivering fuel into the combustion chamber of an engine. The spark ignition requires a spark to initiate combustion in the chamber. The EMS determines the quantity of fuel to inject based on a number of parameters recorded by the sensors. The EMS therefore controls the both the amount of fuel to be injected as well as the exact time of spark generation (ignition timing) to provide better power and combustion. The following are some of the methods used by an EMS to calculate the spark advance and fuel injection quantity for an open loop control system. The ignition in an open loop system is based on programmed information in the EMS. Ignition timing is selected on the basis of measures that are transmitted from the sensors such as the manifold pressure or coolant temperature (Stone and Ball 2004). The fuel air ratio should be 14.7 parts of air into 1 part of fuel. This ratio is maintained by the electronic fuel injection system (EFI). It controls the amount of fuel injected into each cylinder. The open loop mode of operation utilizes a digital computer and a throttle body fuel-metering actuator and a set of sensors as discussed above. The computer then processes the signals to determine the correct fuel flow rate fixed by time to open the fuel injectors. These injectors are solenoid in nature. The following systems calculate the fuel injection in a open loop system (Horner, 2014) The mass air flow electronic fuel injector. The mass airflow sensor is normally fitted near the air filter box or near the throttle. It measures the volume of air going to the engine and transmits its recordings to the EMS. The EMS then uses them to calculate the volume of fuel needed to be injected. The most common type of mass flow air sensor is the hot wire design. Here, air flows over a heated wire whose temperature is above the inlet air. The air draws away heat as it flows therefore the amount of heat needed to hit the wire is directly proportional to the amount of air (Davis 2001). The EMS compares the mass air inflow with other sensors data and determines the engine’s state. It then refers to the electronic map to find the appropriate air/fuel ratio. After determining this, it selects the fuel injector pulse width required to meet the input signals. Use of speed density The speed sensors normally measure the speed of the engine in rotations per minute and load. The mass air flow is directly proportional to fuel injection and this leads to steady and constant ratio between the two. The mass airflow affects the manifold absolute pressure (MAP).The EMS uses the MAP to calculate the air flow and the fueling requirements. Therefore, the use of speed density in calculating the fuel ejection is highly sensitive to temperature since temperature affects the density of air. Production based speed density computers also utilize information from the oxygen sensor mounted on the exhaust. The computer compares the air to fuel ratio and then adjusts the fuel delivery. These promote complete combustion of fuel (Horner, T. H, 2014) A knock sensor is also utilized in the speed density method of measurement. It detects the vibrations emitted from the engine and then delays ignition time of the fuel and air. This prevents damage of the engine from excessive pressures. Comparison between the two methods According to Horner (2014), The Mass Air Flow is normally more accurate as compared to the speed density method. This is because the density of air is affected by many parameters for example temperature. This therefore makes it important to control the temperature in a speed density method. The use of MAF can also tolerate major engine changes. The speed density systems do not tolerate major engine changes without computer reprogramming. Such reprogramming normally requires a specialist. Method used to calculate spark advance Ignition timing system provides an electric spark at the proper timing for combustion to occur. The system uses data from the sensors to determine the best time to ignite. It uses manifold pressure data, engine rotations per minute, crankshaft position and temperature data. The ignition system must be timely to ignite and promote proper flame propagation. The timing should also prevent knocking therefore avoid ignition when the pressures in the combustion cylinder are high. This would damage the cylinder. The following parameters assist in the EMS in determining the ignition timing in the following way.MAP: if the MAP is increased, the spark ignition is decreased to prevent knocking (Andrew, 2014.) The correction of MAP is first done before ignition in case it is too high. Engine RPM; the RPM data helps the EMS to determine the spark advance. Generally, the spark advance increases with increase in the engine RPM until a certain maximum is reached upon which the ignition spark remains constant. Knock sensor: it senses the presence of excessive pressures in the cylinders. This helps the EMS in delaying the ignition timing, as this would damage the cylinder. The ignition spark is then delivered once the knock has ceased. Modification of an open loop to a closed loop using lambda (oxygen) sensor The open loop system does not provide feedback of the result of the EMS. There is no sensing of the exhaust gas concentration to determine the oxygen concentration and combustion. The open loop system ignores the Lambda (oxygen) therefore the decisions of the EMS are based entirely on the Manifold Air Pressure sensor (Hilliard 1994)The closed loop system contains a Lambda sensor which measures the concentration of oxygen in the exhaust gas and gives a feedback to the EMS. This helps it to adjust the air flow rate. This is important in maintaining the air fuel ratio. An open loop system can be modified to a closed loop system by fitting a lambda sensor. This sensor could be a narrow band sensor or a wide band sensor. These sensors analyze the composition of exhaust gas and give feedback to the EMS so as to adjust the air fuel mixture ratio. This changes the composition of the exhaust gases thereby reducing the harmful emissions that are not completely combusted. The closed loop also promoted the efficient operation of a 3 way catalytic converter. These converters chemically change the exhaust gas constituents to reduce emissions of hydrocarbons. They utilize the information obtained from the lambda sensors. They remove 98 % of exhaust harmful gases by turning any carbon based gas to carbon (IV) oxide (Andrew, 2014.) The lambda sensor tells the EMS the state of the gas. The EMS then adjusts to make the ratio ideal and by so doing, it uses its output which is the composition of the exhaust gas to modify input. This leads to less harmful emissions. How control can be extended using sensor information from a knock sensor. A knock sensor is a piezoelectric device that generates some voltage when exposed to vibration. Sensor signal varies in amplitude depending on the intensity of knock. The signals helps the EMS to retard the ignition timing to compensate for the knocking which protects the pistons of the engine from damage (Horner 2014) Combustion knock normally cause the engine to vibrate due to cylinder pressure. The knock sensor information helps to identify the knocking cylinder. As a result, ignition timing is delayed on that cylinder. This prevents damage from the excessive pressure. Knock sensors signal feedback and determine the degree of detonation taking place. This is normally accomplished by filtering out other background noise and vibrations. This leads to retardation of ignition only when real vibrations are present. Control can be extended using the knock sensor information by helping the engine to generate optimum spark timing. This ensures that the engine run on the knock threshold. This impeccable timing of the spark leads to better engine performance. The information can also be used in controlling each cylinder individually. This ensures that all the cylinders in the engine are running at the knock threshold. This ensures best spark timing and provides the best power and fuel efficiency (Hilliard, 1994). The knock threshold is the point where the power and fuel supply is at its best. The combustion at the knock threshold is smooth from the point of ignition to the cylinder walls. The pressure of the unburned fuel /air mixture is at the desired level for ignition to occur. The benefits and issues of EMS control of wide-band lambda sensors Lambda sensors analyze the composition of exhaust gas after combustion and provide feedback to the EMS for it to adjust the air fuel ratio for complete combustion to occur. The correct air fuel ratio also known as stoichiometric ratio should be 14.7:1 ideally. The wide band lambda sensor is located in the exhaust stream and measures the oxygen in the exhaust gas. It then transmits this information to the EMS which maintains the amount of fuel injected into the engine to compensate for excess air or excess fuel. This promotes complete combustion and reduces the amount of toxic emissions (Hilliard, 1994) The wide band lambda sensor works by using a supplied voltage to create a chemical reaction. The chemical reaction in turn creates a current based on the gas mixture. These sensors have to be heated for them to work properly. The benefit of wide band sensors is that they result in most efficient combustion (Norman 2014) this is achieved by ensuring proper fuel to air ratio. As a result, there is a reduction in the hydrocarbon emissions that are normally as a result of incomplete combustion. Conclusion In conclusion, Apart from promoting efficient combustion, the lambda sensors also promote excellent fuel economy. This is by ensuring complete combustion of fuel takes place for energy needed. This reduces the fuel wastages. They also promote efficient catalyst action. The catalysts normally convert the exhaust gas to less polluting. They use information from the lambda sensors to carry out the chemical conversion of the exhaust gas. They also need a certain operating temperature. Finally, the wide band lambda sensors lead to a closed loop system which is more efficient as it utilizes the feedback to adjust the fuel air ratio. References Andrew, D. (2014.). Teglerizer retrieved from http://www.teglerizer.com/fi/bem/Basics of engine management.html [Accessed 15 Nov. 2014]. Davis, M. (2001). Electronic Fuel Injection Mass Flow vs. Speed Density- Car Craft Magazine. [online] Hot Rod. Available at: http://www.hotrod.com/how-to/engine/electronic-fuel-injection [Accessed 15 Nov. 2014]. Hilliard, J. (1994). Fuel injection system in an open loop. In Fuel economy in road vehicles powered by spark ignition engines. New York: Plenum Press. Horner, T. H, (2014). Knocking. Engine knock detection using spectral analysis techniques, 1, 7-62. Norman, J. (2014). Affordable Fuel Injection - How Fuel Injection Works. [online] Affordable-fuel-injection.com. Available at: https://www.affordable-fuel- injection.com/how-fuel-injection-works.html [Accessed 15 Nov. 2014]. Obdii (2014). Introduction to engine management systems. [online] Available at: http://www.obdii.com/articles/Intro_to_Engine_Management.html [Accessed 15 Nov. 2014]. Stone, R. and Ball, J. (2004). Automotive engineering fundamentals. Warrendale, Pa.: SAE International. Uk.vdo (2014). VDO - Fuel Supply Systems. Retrieved on 17th/ 11/2014from http://uk.vdo.com/generator/www/uk/en/vdo/main/products_solutions/passenger_cars/replacement_parts/fuel_supply_systems/fuel_systems_en.html [Accessed 15 Nov. 2014]. Read More