The greatest source of GHG reductions from vehicle in the near and medium term comes from advances in traditional and hybridized internal combustion engine technology. There is a clean opportunity to improve new car fuel economy 30% or more by 2020 and 50% by 2030 at low costs taking into account lifetime fuel savings. Considering the internal combustion engine will continue to dominate the world vehicle fleet in the short and medium term, advances in ICE fuel economy technologies holds the greatest promise to GHG reductions in the road transport sector.
Below is a discussion of different technologies currently available, which offer increases in fuel economy and reduced GHG emissions in an internal combustion engine.
Almost every engine manufacturer is researching options to reduce engine friction losses.
Currently, a lot has been done in this field. For example advanced outlining of the crank with the cylinder concepts has been proposed in which the friction of the piston can be lowered. For advanced techniques we can also think of coatings that will be used in the cylinder and on the piston. At this time a trend is seen of electrifying the auxiliaries which also reduces the engine friction losses. Other friction losses which can be lowered are rolling element bearings, rolling contacts, bore out-of-round/block deformation and ring tension.
In internal combustion engines, gasoline direct injection is a latest variant of fuel injection employed in modern four- stroke petrol engines. The petrol/gasoline is highly pressurized, and injected via a common rail fuel line directly into the combustion chamber of each cylinder, as opposed to conventional multi-point fuel injection that happens in the intake tract, or cylinder port.
In some applications, gasoline direct injection enables stratified fuel charge (ultra lean burn) combustion for improved fuel efficiency, and reduced emission levels at low load.
The major advantages of a GDI engine are increased fuel efficiency and high power output. In addition, the cooling effect of the injected fuel and the more evenly dispersed mixtures allow for more aggressive ignition timing curves. Emissions levels can also be more accurately controlled with the GDI system. The cited gains are achieved by the precise control over the amount of fuel and injection timings which are varied according to the load conditions. In addition, there are no throttling losses in some GDI engines, when compared to a conventional fuel injected or carbureted engine, which greatly improves efficiency, and reduces “pumping losses” in engines without a throttle plate. Engine speed is controlled by the engine control unit/engine management system (EMS), which regulates fuel injection function and ignition timing, instead of having a throttle plate which restricts the incoming air supply. Adding this function to the EMS requires considerable enhancement of its processing and memory, as direct injection plus the engine speed management must have very precise algorithms for good performance and driveability.
Potential fuel economy benefit – [2-8%]
Homogeneous Charge Compression Ignition (HCCI) has characteristics of the two most popular forms of combustion used in IC engines: homogeneous charge spark ignition (gasoline engines) and stratified charge compression ignition (diesel engines). As in homogeneous charge spark ignition, the fuel and oxidizer are mixed together. Rather than using an electric discharge to ignite a portion of the mixture, the density and temperature of the mixture are raised by compression until the entire mixture reacts spontaneously. Stratified charge compression ignition also relies on temperature and density increase resulting from compression, but combustion occurs at the boundary of fuel-air mixing, caused by an injection event, to initiate combustion.
The defining characteristic of HCCI is that the ignition occurs at several places at a time which makes the fuel/air mixture burn nearly simultaneously. There is no direct initiator of combustion. This makes the process inherently difficult to control. However, with advances in microprocessors and a physical understanding of the ignition process, HCCI can be controlled to achieve gasoline engine-like emissions along with diesel engine-like efficiency. In fact, HCCI engines have been shown to achieve extremely low levels of Nitrogen oxide emissions (NOx) without after treatment. The unburned hydrocarbon and carbon monoxide emissions are still high (due to lower peak temperatures), as in gasoline engines, and must still be treated to meet emission regulations. HCCI provides up to a 30-percent fuel savings.
Camless valve activation refers to the elimination of the camshaft that has been used in engines for many years. This is the ultimate evolution of variable valve timing. In this system, valves are controlled by either electromechanical or electrohyrdaulic means with no camshaft present. So, valves can be opened or closed whenever desired, no longer dependent on the cam lobes on the camshaft to operate. These systems will come into production in the next few years. More work needs to be done on the noise and other issues related to their use.
Cylinder deactivation is a technology where the intake and exhaust valves are disabled and prevents fuel injection into some of the cylinders during light load operation. The engine runs temporarily as though it were a smaller engine which substantially reduces pumping losses and improves efficiency.
Turbo or supercharged engines increases the available airflow and specific power level, allowing a reduced engine size while maintaining performance. A supercharger is an air compressor used for forced induction of an internal combustion engine. The greater mass flow-rate provides more oxygen to support combustion than would be available in a naturally-aspirated engine, which allows more fuel to be provided and more work to be done per cycle, increasing the power output of the engine. A supercharger can be powered mechanically by a belt, gear, shaft, or chain connected to the engine's crankshaft.
Turbo-charging uses the exhaust gases to compress the air. Sequential twin-turbo refers to a set up in which the motor utilizes one turbocharger for lower engine speeds, and a second or both turbochargers at higher engine speeds. During low to mid engine speeds, when available spent exhaust energy is minimal, only one relatively small turbocharger, the primary turbocharger, is active. During this period, all of the engine's exhaust energy is directed to the primary turbocharger only, lowering the boost threshold, minimizing turbo lag, increasing power output at low engine speeds and providing the benefits of a small turbo. Towards the end of this cycle, the secondary turbocharger is partially activated (both compressor and turbine flow) in order to pre-spool the secondary turbocharger prior to its full utilization. Once a preset engine speed or boost pressure is attained, valves controlling compressor and turbine flow through the secondary turbocharger are opened completely (the primary turbocharger is deactivated at this point in some applications). At this point the engine is functioning in a full twin-turbocharger form, providing the benefits associated with a large turbo, including maximum power output, without the disadvantages such as increased turbo lag. Either of these devices allows downsizing of the engine, resulting in more fuel efficiency. Potential fuel economy benefit – [2-5%]