Topics Tagged ‘Engine’
Nowadays concerns about methanol have increased from the viewpoints of environmental protection and versatility of fuels at a global scale. Energetic research on methanol-fueled automobile engines has been forwarded from the viewpoints of low environmental pollution and the use of alternate fuel since the oil crisis, and they are now being tested on vehicles in various countries in the world. Desire for saving of maintenance cost and labour prevails as well as the environmental problems in the field of marine engines. From these motives scientists have carried out research and development of a methanol fueled marine diesel engine which is quite different from automobile engines in the size, main particulars, working condition and durability.
Although scientists have made a great use of invaluable knowledge from automotive technology, some special studies were necessary due to these differences. Ignition method is a typical one. Dual fuel injection system was tried for trouble-free ignition of methanol fuel. This system is thought to be the most favourable ignition method for marine diesel engines which have to withstand quick load change and accept no misfiring.
Rocket engines that work much like an automobile engine are being developed at NASA’s Marshall Space Flight Center in Huntsville, Ala. Pulse detonation rocket engines offer a lightweight, low-cost alternative for space transportation. Pulse detonation rocket engine technology is being developed for upper stages that boost satellites to higher orbits. The advanced propulsion technology could also be used for lunar and planetary Landers and excursion vehicles that require throttle control for gentle landings.
The engine operates on pulses, so controllers could dial in the frequency of the detonation in the “digital” engine to determine thrust. Pulse detonation rocket engines operate by injecting propellants into long cylinders that are open on one end and closed on the other. When gas fills a cylinder, an igniter—such as a spark plug—is activated. Fuel begins to burn and rapidly transitions to a detonation, or powered shock. The shock wave travels through the cylinder at 10 times the speed of sound, so combustion is completed before the gas has time to expand. The explosive pressure of the detonation pushes the exhaust out the open end of the cylinder, providing thrust to the vehicle.
A major advantage is that pulse detonation rocket engines boost the fuel and oxidizer to extremely high pressure without a turbo pump—an expensive part of conventional rocket engines. In a typical rocket engine, complex turbo pumps must push fuel and oxidizer into the engine chamber at an extremely high pressure of about 2,000 pounds per square inch or the fuel is blown back out.
The pulse mode of pulse detonation rocket engines allows the fuel to be injected at a low pressure of about 200 pounds per square inch. Marshall Engineers and industry partners United Technology Research Corp. of Tullahoma, Tenn. and Adroit Systems Inc. of Seattle have built small-scale pulse detonation rocket engines for ground testing. During about two years of laboratory testing, researchers have demonstrated that hydrogen and oxygen can be injected into a chamber and detonated more than 100 times per second.
NASA and its industry partners have also proven that a pulse detonation rocket engine can provide thrust in the vacuum of space. Technology development now focuses on determining how to ignite the engine in space, proving that sufficient amounts of fuel can flow through the cylinder to provide superior engine performance, and developing computer code and standards to reliably design and predict performance of the new breed of engines.
A developmental, flight-like engine could be ready for demonstration by 2005 and a full-scale, operational engine could be finished about four years later. Manufacturing pulse detonation rocket engines is simple and inexpensive. Engine valves, for instance, would likely be a sophisticated version of automobile fuel injectors. Pulse detonation rocket engine technology is one of many propulsion alternatives being developed by the Marshall Center’s Advanced Space Transportation Program to dramatically reduce the cost of space transportation.
Compared with petrol, diesel is the lower quality product of petroleum family. Diesel particles are larger and heavier than petrol, thus more difficult to pulverize. Imperfect pulverization leads to more unburnt particles, hence more pollutant, lower fuel efficiency and less power.
Common-rail technology is intended to improve the pulverization process. Conventional direct injection diesel engines must repeatedly generate fuel pressure for each injection. But in the CRDI engines the pressure is built up independently of the injection sequence and remains permanently available in the fuel line. CRDI system that uses an ion sensor to provide real-time combustion data for each cylinder. The common rail upstream of the cylinders acts as an accumulator, distributing the fuel to the injectors at a constant pressure of up to 1600 bar. Here high-speed solenoid valves, regulated by the electronic engine management, separately control the injection timing and the amount of fuel injected for each cylinder as a function of the cylinder’s actual need.
In other words, pressure generation and fuel injection are independent of each other. This is an important advantage of common-rail injection over conventional fuel injection systems as CRDI increases the controllability of the individual injection processes and further refines fuel atomization, saving fuel and reducing emissions. Fuel economy of 25 to 35 % is obtained over a standard diesel engine and a substantial noise reduction is achieved due to a more synchronized timing operation. The principle of CRDi is also used in petrol engines as dealt with the GDI (Gasoline Direct Injection) , which removes to a great extent the draw backs of the conventional carburetors and the MPFI systems.
CRDi stands for Common Rail Direct Injection.