09-11-2012, 03:59 PM
RECENT ADVANCES IN IC ENGINES
RECENT ADVANCES IN IC ENGINES.doc (Size: 2.54 MB / Downloads: 49)
Abstract
The key drivers for new engine technology namely
•Changing Customer Expectations.
• New Environmental Regulations on Emissions & Noise.
• Increasing Fuel Costs.
• Availability of Alternate Fuels.
• New Emerging Markets & Segments.
• Increasing Competition
are causing today’s engineers to think in the direction of more efficient and economical engines. Despite large improvements in engine efficiency over many years the average fuel consumption remained the same between 1985 to 1998. CO2 emissions are directly proportional to fuel consumption and believed to be contributing to the increase in global temperature. Thus improvement of fuel economy is a most critical challenge facing the engineers.
New technology in various IC engine systems, be it the fuel system, ignition system, designs of crankshafts, valves, pistons etc. alongwith the application of non-related fields like Thermography to IC engines may help in realizing the full potential of IC engines. Preference is now being given to cost effective means of exhaust emission control involving new designs of engine parts than the more complex “exhaust after treatment processes”. Recent IC engines have already reached significant levels of performance thanks to continual research in engine design and technology. The new designs have totally changed the way a conventional IC engine used to work!
Introduction
It is no accident that as the twenty-first century dawns, engine manufacturers have stepped up the pace of IC engine development to a speed not seen in the century or so since the first IC engine was patented. Like so many other technical developments in history, the current progress in IC engine technology is the result of several seemingly unconnected developments. This paper describes various such developments in the field.
Latest Technologies in Internal Combustion engines:
Variable Valve Timing
Several engine manufacturers are experimenting with systems that would allow infinite variability in valve timing. The camshafts on some Ferrari engines are cut with a three-dimensional profile that varies along the length of the cam lobe. At one end of the cam lobe is the least aggressive cam profile, and at the other end is the most aggressive. The shape of the cam smoothly blends these two profiles together. A mechanism can slide the whole camshaft laterally so that the valve engages different parts of the cam. The shaft still spins just like a regular camshaft -- but by gradually sliding the camshaft laterally as the engine speed and load increase, the valve timing can be optimized.
Valvetronic Engines:
The Valvetronic engine is the world's first engine without a throttle butterfly. Valvetronic varies the timing and the lift of the intake valves. The Valvetronic system has a conventional intake cam, but it also uses a secondary eccentric shaft with a series of levers and roller followers, activated by a stepper motor. Based on signals formerly taken mechanically from the accelerator pedal, the stepper motor changes the phase of the eccentric cam, modifying the action of the intake valves. Valvetronic reduces maintenance costs, improves cold start behavior, lowers exhaust emissions, and provides a smoother running engine. Valvetronic does not need specific fuel grades or fuel qualities because of its fine atomization of fuel. Because Valvetronic allows the engine to breathe more freely, fuel consumption is reduced by 10%. Valvetronic minimizes “pumping loss” by reducing valve lift and the amount of air entering the combustion chambers.
Compared with conventional twin-cam engines with finger followers, Valvetronic employs an additional eccentric shaft, an electric motor and several intermediate rocker arms, which in turn activates the opening and closing of valves. If the rocker arms push deeper, the intake valves will have a higher lift, and vice-versa. Thus, Valvetronic has the ability to get deep, long ventilation (large valve lift) and flat, short ventilation (short valve lift), depending on the demands placed on the engine.
New Teflon Pads pistons:
The Cummins V28 engines have used a new technology for their pistons- they have two teflon pads and the pistons also incorporate a cutback headland. Extensive testing in laboratory and field has shown that the Teflon padded pistons will eliminate cylinder liner water jacket cavitation corrosion and increase cylinder liner life and hence engine life. The cutback feature has been found to consistently reduce oil consumption and blobye. The advantages include:
1. Improved oil consumption
2. Increased piston and cylinder liner life
Pads are removable and interchangeable Teflon pad (piston need not be replaced since the wear takes place only on the Teflon pads).
Variable Compression Ratio:
This technology makes use of the fact that change in the compression ratio in the cylinder improves its performance.