Every time the plug sparks, minute particles of material are worn away from the electrodes. This phenomenon is called spark erosion. Over time, this process increases the spark plug gap between the centre and the earth/ground electrode. If the gap becomes too large, misfi ring will occur.
To extend the service interval of vehicles, the service life of the spark plug must be increased.
Some manufacturers are fi tting multi electrode Safety fi rst
Sight and hearing impaired people can be particularly vulnerable so drivers need to be aware of this and take extra care.
169
spark plugs as original equipment to achieve this.
Multi electrode spark plugs can have two, three or four ground electrodes depending on the service life requirement of the manufacturer. However, no matter how many ground electrodes the plug has, every time the spark plug fi res, only one spark occurs between the centre electrode and the ground electrode, which has the lowest required voltage or the least distance to travel between the centre and the ground electrode.
Key fact
No matter how many ground electrodes the plug has, every time the spark plug fi res, only one spark occurs between the centre electrode and the ground electrode
The spark plug plays a vital role in the quest to improve ignition quality, engine performance, reduce emissions and reduce fuel consumption. Spark plugs that employ small diameter centre and sometimes ground electrodes can offer benefi ts in several areas. These fi ne wire plugs require less voltage to create the spark, have a more consistent spark position, better gas fl ow around the fi ring position and experience less quench effect than other designs. As the electrodes erode during use it is necessary to compensate for the use of smaller electrodes by some means, otherwise the plugs would have an unacceptable (short) service life.
Key fact
Fine wire plugs require less voltage to create a spark.
By using small chips of special precious metals such as platinum or even iridium which are welded to the tips of the electrodes it is possible to increase the service life signifi cantly whilst maintaining the highest ignition performance. These metals are extremely hard and have very high melting points thus making them ideal for use in this hostile environment.
Safety fi rst
Remember, all ignition systems are high voltage.
Some modern vehicles use a direct fuel injection system and these vehicles demand high ignition quality and extreme anti-fouling performance.
NGK has developed a plug that has several special features designed to offer the required performance.
Essentially, a very projected fi ne wire spark plug with platinum electrodes is combined with a semi-
surface discharge design. The resulting plug has three ground electrodes, two of which are mostly redundant unless in extreme circumstances the plug becomes very carbon fouled. At this point the spark will discharge across the insulator nose to one of the side electrodes preventing a misfi re and unburned fuel reaching the catalyst. This type of plug must only be use in the specifi c applications as listed in the NGK catalogues.
2.8.2 V6 diesel with electric turbocharging
Audi’s new (2017/18) V6 diesel includes a new electrically enhanced turbocharger system, as well as a new integrated NOx and PM after treatment suite. It is expected that in the year 2030, more than 80% of newly registered cars and light trucks will still have an internal combustion engine on board and the number of diesel engines is likely to remain stable at today’s levels. Many of those diesels could be electrically turbocharged. This is likely due to the uptake of diesel engines in the USA.
Figure 2.320 Spark plug electrodes, left to right: multi- electrode, iridium wire, hybrid. (Source: NGK Plugs)
Figure 2.321 Audi V6 diesel with electric turbo.
(Source: Audi Media)
170
Defi nition
PM: Particulate matter.
NOx:Nitrogen oxides.
It is claimed that using the e-turbo will easily gain you a lead of at least two car lengths in the fi rst two seconds at the traffi c lights! This illustrates the clear benefi t of the system in that turbo lag is all but eliminated as the turbo compressor can be brought up to speed almost instantly. Other new features are to be incorporated:
Piston rings have been optimized for minimal friction.
The crankcase and new cylinder heads have separate coolant loops.
A new thermal management system improves effi ciency.
The turbocharger and the fully variable-load oil pump have been updated.
The engine will include a NOx storage catalytic converter that has been combined with a diesel particulate fi lter and SCR injection in a single unit.
Defi nition
SCR: Selective catalytic reduction.
The engine package satisfi es the most stringent of emissions legislation, including Euro 6 and reduces CO2 emissions by an average of 15 g/km. Emission and economy issues are what manufacturers are working towards with all their new developments.
2.8.3 Water injection
Even advanced petrol/gasoline engines waste roughly a fi fth of their fuel. This is mostly at high engine speeds, where some of the fuel is used for cooling instead of for propulsion. Water injection means that it does not have to be that way. Particularly when accelerating quickly or driving on the motorway, the injection of additional water makes it possible to reduce fuel consumption by up to 13%.
Key fact
Even advanced petrol/gasoline engines waste roughly a fi fth of their fuel.
The fuel economy offered by this Bosch technology comes especially to the fore in three- and four- cylinder downsized engines: in other words, in precisely the kind of engines to be found in any average midsize car.
This technology can make cars more powerful as well. Water injection can deliver an extra kick in any turbocharged engine. This is because earlier ignition angles mean that the engine is operated even more effi ciently. On this basis, engineers can coax additional power out of the engine, even in powerful sports cars.
The basis of this innovative engine technology is a simple fact: an engine must not be allowed to overheat. To stop this happening, additional fuel is injected into nearly every SI engine on today’s roads.
This fuel evaporates, cooling parts of the engine block.
With water injection, Bosch engineers have exploited this physical principle. Before the fuel ignites, a fi ne mist of water is injected into the intake duct. Water’s high heat of vaporization means that it provides effective cooling.
Key fact
Water’s high heat of vaporization means that it provides effective cooling.
This is also the reason only a small additional volume of water is needed: for every one hundred kilometres driven, only a few hundred millilitres are necessary.
As a result, the compact water tank that supplies the injection system with distilled water only has to be refi lled every few thousand kilometres. If the tank should run empty, the engine will still run smoothly, albeit without the higher torque and lower consumption provided by water injection.
Figure 2.322 Water injection can produce extra boost for the turbocharged engine. (Source: Bosch Media)
171 2.8.4 Cylinder deactivation
The purpose of cylinder deactivation technology is to reduce fuel consumption on petrol/gasoline engines.
Large capacity engines were renowned for poor fuel consumption under low speed and torque conditions.
This ineffi ciency is known as pumping loss and is used to describe a situation where an engine that is unable to draw in a suffi cient quantity of air and fuel mixture on the inlet stroke, to produce high cylinder pressure during compression.
Low pressure in an engine cylinder results in low effi ciency because more fuel is required to compensate for the lack of pressure and the ability to draw fuel into the cylinder. To deactivate a cylinder of a running engine whilst retaining balance, driveability and emission targets is a challenge. The best method of deactivation, therefore, is to disconnect the valve operating mechanism. If the inlet and exhaust valves of the deactivated cylinder are closed, no gases can enter or exit. This also prevents an increase in exhaust emissions. Fuel injection to the deactivated cylinder is also switched off.
Key fact
Low pressure in an engine cylinder results in low effi ciency because more fuel is required to compensate for the lack of pressure
Volkswagen use a cylinder deactivation technology on smaller engines (1.4 lt. for example). Their method employs a system of cam lobes that are splined to the camshafts. In the normal working position the cam lobes are aligned with the valves. To deactivate the cylinder a pin is engaged with a scroll that moves the cams out of alignment with the rockers and prevents the valve from opening. The pin is solenoid operated.
In this state the valve rockers run on a concentric part
of the shaft. After the sliding component has moved, the pin is retracted. To re-activate the valves a second pin is engaged with the scroll and the cams move back to their normal position. The switchover process occurs during half of a camshaft rotation.
The VW active cylinder technology (ACT) system shuts down the second and third cylinders during low and medium loads and therefore reduces fuel consumption. It is active over an engine speed range of 1400 to 4000 rpm a torque output range of about 25 to 100 Nm. When the driver demands acceleration, this is detected by the pedal sensor and both cylinders are re-activated without any noticeable change. The system has no detrimental effects on smooth running of the engine. Changes are made to ignition timing and the throttle valve position to ensure a smooth transition. If the system detects irregular driving, cylinder shut-off is deactivated.
Honda use a different deactivation system. This employs rockers that are connected and disconnected by hydraulically operated locking pins. One rocker always remains in contact with the profi le of the cam and, when connected by the pin, operates a second rocker that in turn operates the valve. When deactivation is required oil pressure, controlled by a solenoid valve, forces the locking pin out of engagement with the second rocker. This prevents the valve from opening. This technology has been used in hybrid models since the year 2000.
The Bosch cylinder deactivation system can facilitate the deactivation of cylinders that are not required within part-load operations in almost every gasoline engine. This saves fuel and thus reduces CO 2
Figure 2.323 Valves operating normally (left), valve closed (right) and cylinder deactivated.
(Source: Volkswagen Media) Figure 2.324 Honda cylinder deactivation mechanism
172
emissions. The Bosch system deactivates the hydraulic valve lifters to prevent the valves opening.
This section has outlined three methods of cylinder deactivation:
locking pins and a second rocker splined moveable cams
deactivation of hydraulic lifters.
It is quite likely that more methods will be introduced because the system has great potential for reducing consumption and emissions.
2.8.5 Dynamic skip fi re
Dynamic Skip Fire (DSF) is an interesting extension of cylinder deactivation technology in which any of the cylinders for automobile engines are fi red or skipped (deactivated) on a continuously variable basis. The engine control system commands the appropriate number and sequence of fi red cylinders to deliver the instantaneous torque demanded from the engine. This enables fully optimized combustion and reduced engine pumping losses, thereby increasing fuel effi ciency.
Operating the engine in a dynamic skip fi re
manner alters the torque excitations on the vehicle powertrain, which could lead to unacceptable NVH characteristics. Tula’s novel fi ring decision and control algorithms manage noise and vibration algorithmically to maintain a high-quality driving experience.
Defi nition
NVH: Noise vibration and harshness.
This interesting technology from Tula integrates advanced signal processing with sophisticated powertrain controls to create the ultimate variable displacement engine. The result is optimal fuel effi ciency at the lowest cost.
2.8.6 Diesel particulate fi lters
The main approach to lowering of diesel engine emissions comprises internal engine improvements.
This is because improved fuel combustion prevents, as far as possible, the formation of pollutants and reduces fuel consumption. In this respect, automobile manufacturers and their component suppliers have already achieved a great deal.
A diesel particulate fi lter (DPF) is a device designed to remove diesel particulate matter or soot from the exhaust gas of a diesel engine. Wall-fl ow diesel particulate fi lters usually remove 85% or more of the soot and under certain conditions can attain soot removal effi ciencies of close to 100%.
Defi nition
DPF: Diesel particulate fi lter.
The most common fi lter is made of cordierite (a ceramic material that is also used as catalytic converter cores). Cordierite fi lters provide excellent fi ltration effi ciency, are (relatively) inexpensive, and have thermal properties that make packaging them for installation in the vehicle simple. The major drawback is that cordierite has a relatively low melting point (about 1200°C) and cordierite substrates have been known to melt down during fi lter regeneration. This is mostly an issue if the fi lter has become loaded more heavily than usual, and is more of an issue with passive systems than with active systems, unless there is a system breakdown.
Cordierite fi lter cores look like catalytic converter cores that have had alternate channels plugged – the plugs force the exhaust gas fl ow through the wall and the particulate collects on the inlet face.
Figure 2.325 DSF Operation tracking engine
torque demand. (Source: Tula, www.tulatech.com) Figure 2.326 Cordierite fi lter cores
173
The second most popular fi lter material is silicon carbide, or SiC. It has a higher (2700°C) melting point than cordierite, however it is not as stable thermally, making packaging an issue. Small SiC cores are made of single pieces, while larger cores are made in segments, which are separated by special cement so that heat expansion of the core will be taken up by the cement, and not the package. These cores are often more expensive than cordierite ones, however they are manufactured in similar sizes, and one can often be used to replace the other.
Ceramic fi bre fi lters are made from several different types of ceramic fi bres that are mixed together to form a porous media. This media can be formed into almost any shape and can be customized to suit various applications.
The particulate fi lter shown as Figure 2.327 is made of sintered metal and lasts considerably longer than current ceramic models, since its special structure offers a high storage capacity for oil and additive combustion residues. The fi lter is designed in such a way that the fi ltered particulates are very evenly deposited, allowing the condition of the fi lter to be identifi ed more reliably and its regeneration controlled far better than with other solutions. This diesel particulate fi lter is designed to last as long as the vehicle itself.
The two main DPF systems are those with additive and those without. To enable a vehicle to operate without an additive the particulate fi lter must be fi tted close to the engine. Because the exhaust gases will not have travelled far from the engine they will still be hot enough to burn off the carbon soot particles.
In these systems, an oxidising catalytic converter will be integrated into the particulate fi lter. In other systems, the particulate fi lter is fi tted some distance from the engine and as the exhaust gases travel along
the exhaust they cool. The temperatures required for ignition of the exhaust gas can only be achieved using an additive.
Use of an additive lowers the ignition temperature of the soot particles and, if the engine management ECU raises the temperature of the exhaust gas, the fi lter can be regenerated. Regeneration is usually necessary after between 300 and 450 miles, depending on how the vehicle is driven. The process takes about 5–10 minutes and the driver shouldn’t notice it is occurring, although sometimes there may be a puff of white smoke from the exhaust during regeneration. The additive is stored in a separate tank and is used at a rate of about 1 litre of additive to 3000 litres of fuel. It works by allowing the carbon particles trapped in the particulate fi lter to burn at a signifi cantly lower temperature than would usually be required (250–450 oC rather than 600–650oC).
On-board active fi lter management can use a variety of strategies:
engine management to increase exhaust
temperature through late fuel injection or injection during the exhaust stroke (the most common method)
use of a fuel borne catalyst (the additive) to reduce soot burn-out temperature
a fuel burner after the turbo to increase the exhaust temperature
a catalytic oxidizer to increase the exhaust temperature, with after injection
resistive heating coils to increase the exhaust temperature
microwave energy to increase the particulate temperature.
Not running the regeneration cycle soon enough increases the risk of engine damage and/or Figure 2.327 Diesel particulate fi lter. (Source: Bosch Media)
Figure 2.328 Different fi tting methods for DPF
174
uncontrolled regeneration (thermal runaway) and possible DPF failure.
There are two types of regeneration – passive and active. Passive regeneration takes place, automatically, on motorway-type runs in which the exhaust
temperature is high. If the exhaust is so hot enough to ignite the soot particles, the regeneration process can carry on continuously and steadily across the platinum coated catalytic converter.
Key fact
There are two types of DPF regeneration – passive and active.
Once the storage capacity of the particulate fi lter has been exhausted, the fi lter must be regenerated by passing hot exhaust gases through it which burn up the deposited particulates. To produce the necessary high exhaust gas temperatures, the EDC alters the amount of air fed to the engine as well as the amount of fuel injected and the timing of injection. In addition, some unburnt fuel can be fed to the oxidizing catalytic converter by arranging for extra fuel to be injected during the expansion stroke. The fuel combusts in the oxidizing catalytic converter and raises the exhaust temperature even further.
A signifi cant number of people don’t use motorways so passive regeneration will be possible only occasionally. In the case of a fi lter without additive when the soot loading reaches about 45% the ECU switches off the EGR and increases the fuel injection period so there is a small injection after the main injection. These measures help to raise the engine exhaust temperature to over 600ºC, which is high enough to burn off the soot particles.
A warning light is triggered at a 55% soot loading. In such circumstances the car needs to be driven hard in a lower gear so the temperature in the particulate fi lter will be suffi cient to burn off the soot. If the driver ignores the warning and continues to use the car as normal, the soot will continue to build until it reaches 75%. Additional warnings will then be given using the malfunction indication lamp (MIL). It will not now be possible to clear the DPF by driving and it may
need to be replaced – if loading reaches 95% then the DPF will need to be replaced.
Key fact
The DPF regeneration process that involves heating and burning of the soot is controlled by the engine management system.
2.8.7 Oil fi lter modules
The company Mahle has developed an oil fi lter module that is already installed in over a million vehicles. The unit includes an integrated oil/water heat exchanger.
However, this does not require plumbing into the coolant as it is designed to connect via its baseplate, which is sealed with O rings, and held in place by four simple self-tapping screws.
The housing is a glass fi bre polyamide and has a built-in pressure relief valve. There is also a drain screw on the bottom to prevent spills as the unit is changed.
Another interesting development in oil changing is a complete module that contains the oil and fi lter, and can be changed as one complete unit in just a few minutes. An electric oil pump is used to fi ll the unit Figure 2.329 Sectioned view of a new fi lter
Figure 2.330 Oil fi lter module. (Source: Mahle)