How it Works
All Tunits are specifically designed to achieve enhanced diesel performance by modifying the fuel injection parameters and only by the careful interplay of these values and characteristics can the optimum performance of your engine be achieved. The turbo boost pressure is not directly altered (on turbo models) by the Tunit and is only increased via the natural increase in exhaust gases provided by the increased performance. The design and development of the Tunit has come about by the collaboration of some of the top minds in Europe and is the latest and most advanced device available on the market today. Our ongoing development programme ensures we keep up to date with the latest engine management and injection systems.
Every Tunit is designed to be compact and lightweight, the smallest being only 10cm across, the largest being 13.5cm. In most instances the Tunit comes complete with original manufacturers plugs and connections. An original quality harness to fit in-line is also provided. Most Tunits are fitted in 10-20 minutes and all are designed to be easily installed by people of average mechanical capability. If you prefer, we fit the Tunit for you. Fitting is offered by our international network of world wide distributors. Fitting is usually carried out in less than 20 minutes Fitting at any of our distributors does include a try before you buy so as you can be assured of the performance before you purchase. If you wish to remove the Tunit for either fitting on another vehicle or for any other reason it is just as easy.
Adjustable Tuning
Manual Adjustment - All Tunits are adjustable in one form or another. This allows the Tunit to be individually matched to each and every characteristically different vehicle. This can be very important as two cars the same may not react and drive the same. i.e. one VW Golf 110 bhp may produce 105 bhp, the next Golf built on the same day may produce 115 bhp. For this reason we have built in simple methods of reaching your optimum performance.
The Tunit V-CR, V-PD and V-VP models come pre set for the vehicle.Each Tunit has a 9 position rotary switch. Each position will provide a different power level. 1 is the lowest, 9 is the highest. The Tunit II, III and IV also have a manual adjustment and require a simple adjustment on installation to the vehicle.
Lap top Tune
The V-CR,V-VP & V-PD Tunits also have adjustable tuning via a lap top. This is a form of tune uniquely introduced by our company. Lap top tuning does considerably more than the manual adjustment. Once the Tunit is installed you can actually sit in the drivers seat and the Tunit can be re-programmed, by a Tunit distributor, as you drive along. As well as an overall power increase, the power can be moved further down or up the range and the power delivery can be varied to be smooth or aggressive.
Another great advantage of this is that if you decide to enhance your vehicle further, through maybe induction kits, intercoolers etc. you can easily adjust the Tunit to match the new modification so the full potential can be reached. With fixed map devices and chips this is not possible and a new chip or device would be required.
*We recommend a lap top tune if you add other performance parts such as intercooler and induction kit or if you have specific requirements such as heavy towing or large loads.
What is achieved ?
Immediately the increased power and torque can be felt. The throttle response is improved and particularly low and mid range torque is vastly improved, making the overall performance of the vehicle completely different.
When carrying loads and/or towing, the extra power is a also great advantage. The overall drive becomes more pleasurable and the engine in most instances runs smoother.
In independent tests and trials, results of 7-10% extra better fuel economy have been achieved. This obviously varies from vehicle to vehicle and application.
Warranty & Guarantee
The Tunit and its components comes with a full 3 year warranty. This is transferable with the customer to another vehicle. The warranty can be transferred to a separate customer by applying to Tunit with the original owners cutomer details.
Part Exchanges...
If you are happy with the Tunit product but have changed your vehicle or wish the latest type of Tunit then our part exchange scheme could be your answer. Trade in your faithful and trusty Tunit for a new one and save up 40%.
...and Upgrades
Harness upgrades and reprograms are available also if your new vehicle has a similar injection system to your old.
After sales
Every Tunit customer has the full backup and service from Tunit whilst they own a Tunit product. Queries, installation help, upgrades and support are available from your local distributor
Diesel engines and performance tuning
The only difference between petrol and diesel engines is the fuel/ignition systems. The rest, including the intake, exhaust, and intake and exhaust valves is basically the same.
So all the different methods of getting more power still apply! More airflow equates to more horsepower, so adding a Turbocharger, or a supercharger, or Nitrous Injection all work just fine! Generally chip tuning works too on modern turbo diesels. The same result is produced by manually increasing the boost level, and subsequent fuelling. The only problem is the way the fuel is burned is slow so 5000 rpm is about it for a car diesel engine! All the tuning does is increase torque lower down the rev range. Consequently conventional tuning brings little gain on a diesel.
Never try adding extra diesel fuel via the air intake though! It will pre ignite during the compression cycle... You may run over your own crankshaft! If you need extra fuel because you have fitted a turbo, turned up the boost level, or fitted Nitrous Injection you must either fool the normal injection system into giving more fuel, or add Propane (because it will not ignite due to compression alone) in the intake system.
This works because Propane (or LPG, Methanol, or high octane petrol) have a high Octane Rating. Octane is a measure of the fuels ability to not ignite under compression alone! So the ignition point in a diesel still depends on the normal Diesel injection pump's timing. The extra Propane fuel is ignited by the diesel burning as it Self ignites upon injection via the injector. Diesel is very low Octane, so the heat of compression alone is enough for reliable ignition as it is injected.
The latest models that can be emproved by Diesel Performance Tuning
20-12-2007
AUDI
New A4 TDI 2,0 TDI FROM 2008
CHEVROLET
Captiva 2.0 VCDI
Lacetti 2.0 TCDI
Nubira 2.0 TCDI
DODGE
Avenger 2.0 CRD
FIAT
Scudo 2.0 JTD
Scudo 2.0 JTD
FORD
New Mondeo 2,0 TDCi 2007
Ranger 2,5 TDCI
Transit 2.4 TDCI
Hyundai
i 30 1.6 CRDI
JEEP
Compass 2.0 CRD
Land Rover
Range Rover 3,7 TDV8
MERCEDES
E 420 CDI V8
GL 320 CDI
E 420 CDI V8
E 420 CDI V8
Mitsubishi
Lancer 2.0 DiD
OPEL
Astra D 1,7 CDTI
Astra D 1,7 CDTI
Corsa D 1,7 CDTI
Corsa D 1,7 CDTI
Peugeot
4007 2,2 HDI
Boxer 2.0 HDI
VW
Tiguan 2,0 TDI
Volvo S80 D5
14-06-2007
The Tuningbox® is 100% compatible with Diesel vehicles with particle filters (FAP - DPF)
15-05-2007
Tuningbox® unit now avaible for: :
Alfa Roméo 159 1.9 JTD 120HP & 150HP
Alfa Roméo 166 2.4 JTD 185HP & 200HP
Alfa Roméo 159 2.4 JTD 200 HP
Alfa Roméo 166 2.4 JTD 186 HP
Alfa Roméo 166 2.4 JTD 200 HP
Alfa Roméo Brera 2.4 JTD 200 HP
>
Audi
Audi A4 2.7 TDI V6 180HP
Audi A4 3.0 TDI V6 233 HP
Audi A5 3.0 TDI V6 233 HP
Audi A6 3.0 TDI V6 233HP
Audi Allroad Quattro 2.7 TDI
Audi Allroad Quattro 3.0 TDI
Audi Q7 3.0 TDI
>
BMW
BMW 335D - 730 D 231HP
BMW X3 3.0 D 218HP
BMW X3 3.0 S D 286HP
BMW X5 3.0 D 231HP
>
Cadillac BLS 1.9 D 150HP
>
Chevrolet Captiva 2.0 TDI
Chevrolet Epica 2.0 TDI
>
Citroën C8 2.0 HDI 107HP
C8 2.0 HDI 120HP
Citroën Jumper 2.8 HDI 145HP
Citroën Jumper 3.0 HDI 157HP
Citroën Jumper 2.2 HDI
>
Hyundai i 30 1.6 CRDI
>
Iveco Daily xx-14 HPI 136HP
>
Jaguar X-Type 2.2 D 145CH
>
Jeep Compass 2.0 CRD
>
Ford Fiat Croma 2.4 JTD 200 HP
Fiat Ducato 2.2 HDI
Fiat Punto 1.3 CDTI 90 HP
Ford Focus 2.0 TDCI 136HP
Ford Galaxy 1.8 TDCI 100HP
For S-Max 2.0 TDCI DPF
Ford Transit 2.4 TDCI
>
Jeep Commander 3.0 V6 CRD
KIA Carens 2.0 CRDi 140HP
Kia Ceed 1.6 CRDI
Kia Ceed 2.0 CRDI
Kia Cerato 1.5 CRDI
Kia Cerato 2.0 CRDI
Kia Rio 1.5 CRDI
Kia Cerato 1.6 CRDI
>
Lancia Musa 1.3 JTD 16v
Lancia Phedra 2.0 JTD
Lancia Ypsilon 1.3 JTD 16V
>
Mazda BT 50 2,5 L
>
Mercedes G 320 CDI
Mercedes GL 320 CDI
Mercedes R 280 CDI
Mercedes Sprinter 218 CDI
MercedesSprinter 318 CDI
MercedesSprinter 418 CDI
Sprinter 518 CDI
MercedesViano 3.0 CDI
>
Mini ONE D 1.6
>
MITSUBISHI Outlander 2.0 DiD
Mitsubishi Pajero 3.2 DID 160HP
Pajero 3.2 DID 170HP
Mitsubishi L 200 3.2 DID
>
NISSAN Navara 3.0 150HP
Nissan Note 1.5 dCI
Nissan Qashqai 1.5 Dci
Qashqai 2.0 Dci
>
Opel Corsa 1.3 CDTI
>
Peugeot 807 2.0 HDI 107HP
Peugeot Boxer 2.8 JTD 145HP
Peugeot Boxer 2,2 HDI
Boxer 3.0 JTD Multijet 157HP
>
Renault Clio 1.5 dCI 103HP
Renault Laguna 2.0 dCI DPF 150HP
Renault Megane 2.0 dCi 150HP
Renault New Traffic 2.0 dCI 90HP
Renault New Traffic 2.0 dCi 114 HP
Renault Scenic 2.0 dCi 150HP
Renault Vel Satis 3.0 dCI V6 181HP
>
Seat Leon 2.0 TDI DPF 170HP
>
SSANGYONG Actyon 200 DXI 2.0
>
Toyota Yaris 1.4 D4D-90HP
>
VW Multivan T5 1.9 TDI 102 HP
VW Passat 2.0 TDI 170HP
VW TransVan 1.9 TDI
VW TransVan 2.5 TDI
>
Volvo C 70 2.4 D5
Volvo C 30
Volvo XC 90
Diesel engine
Diesel engines use compression ignition, a process by which fuel is injected after the air is compressed in the combustion chamber causing the fuel to self ignite. By contrast, a gasoline engine utilizes the Otto cycle, in which fuel and air are mixed before ignition is initiated by a spark plug. Most diesel engines have large pistons, therefore drawing more air and fuel which results in a bigger and more powerful combustion. This is effective in large vehicles such as trucks, diesel locomotives and SUV's.
Like many other inventions, the credit for the invention of the diesel engine is in dispute. While Rudolf Diesel is the patent holder and popularly recognized inventor of his namesake engine, Herbert Akroyd Stuart and Charles Richard Binney had previously patented a compression ignition engine designed to run on coal dust. The credit for the invention thus hinges on whether compression ignition or oil fuel is considered the defining property. Diesel's patent (No. 7241) was filed in 1892.[1] However, Herbert Akroyd Stuart and Charles Richard Binney had already obtained a patent (No. 7146) in 1890 entitled: "Improvements in Engines Operated by the Explosion of Mixtures of Combustible Vapour or Gas and Air" which described the world's first compression-ignition engine.[2] Akroyd-Stuart constructed the first compression-ignition oil engine in Bletchley, England in 1891 and leased the rights to Richard Hornsby & Sons, who by July 1892, five years before Diesel's prototype, had a diesel engine working for Newport Sanitary Authority. By 1896, diesel tractors and locomotives were being built in some quantity in Grantham. Importantly, Diesel's airblast injection system did not become part of subsequent "diesel" engines. From around 1910, manufacturers building diesel engines under patent from MAN began building engines with 'solid' injection systems, where fuel is delivered to the cylinder by a high pressure jerk-pump rather than compressed air. This system was invented by Herbert Akroyd Stuart and used on Ruston-built oil engines. MAN continued to build engines to Diesel's original design into the 1920s. By this time Robert Bosch had developed the spring-loaded fuel injector, which provided greater accuracy than the simple nozzle of earlier systems. All mechanical-injection diesel engines built from the 1920s onwards used some form of jerk-pump and spring-nozzle injection. No engine has been built to Diesel's original design since the 1930s.
Early history timeline
* 1862: Nicholas Immel develops his coal gas engine, similar to a modern gasoline engine.
* 1891: Herbert Akroyd Stuart,Wally Godfrey was the brains of the diesel engines Bletchley perfects his oil engine, and leases rights to Hornsby of England to build engines. They build the first cold start, compression ignition engines.
* 1892: Hornsby engine No. 101 is built and installed in a waterworks. It was in the MAN truck museum in Stockport, and is now in the Anson Engine Museum in Poynton. T.H. Barton at Hornsbys builds an experimental version where the vaporiser was replaced with a cylinder head and the pressure increased. Automatic ignition was achieved through compression alone (the first time this had happened), and the engine ran for six hours. Diesel would achieve much the same thing five years later, claiming the achievement for himself.
* 1892: Rudolf Diesel develops the principles of his proposed Carnot heat engine type motor which would burn powdered coal dust. He is employed by refrigeration genius Carl von Linde, then Munich iron manufacturer MAN AG, and later by the Sulzer engine company of Switzerland. He borrows ideas from them and leaves a legacy with all firms.
* 1892: John Froelich builds his first oil engine powered farm tractor.
* 1893: August 10th — Diesel builds a working version of his ideas.
* 1894: Witte, Reid, and Fairbanks start building oil engines with a variety of ignition systems.
* 1896: Hornsby builds diesel tractors and railway engines.
* 1897: Winton produces and drives the first US built gas automobile; he later builds diesel plants. On February 17th, Diesel builds his first working prototype, which narrowly avoids a catastrophic explosion in Augsburg. The engine was not really ready for market until 1908, thanks to other people's improvements.
* 1897: Mirrlees, Watson & Yaryan build the first British diesel engine under license from Rudolf Diesel. This is now displayed in the Anson Engine Museum at Poynton, Cheshire, UK.
* 1898: Busch installs a Rudolf Diesel type engine in his brewery in St. Louis. It is the first in the United States. Rudolf Diesel perfects his compression start engine, patents, and licences it. This engine, pictured above, is in a German museum. Burmeister & Wain (B & W) of Copenhagen, Denmark buy rights to build diesel engines.
* 1899: Diesel licences his engine to builders Krupp and Sulzer, who become famous builders.
* 1902: F. Rundlof invents the two-stroke crankcase, scavenged hot bulb engine.
* 1902: A company named Forest City started manufacturing diesel generators.
* 1903: Ship Gjoa transits the ice-filled Northwest Passage, aided with a Dan kerosene engine.
* 1904: French build the first diesel submarine, the Z.
* 1908: Bolinder-Munktell starts building two stroke hot-bulb engines.
* 1912: First diesel ship MS Selandia is built. SS Fram, polar explorer Amundsen’s flagship, is converted to an AB Atlas diesel.
* 1913: Fairbanks Morse starts building its Y model semi-diesel engine. US Navy submarines use NELSECO units. Rudolf Diesel died mysteriously when he took a ship (SS Dresden) to cross the English Channel.
* 1914: German U-Boats are powered by MAN diesels. War service proves engine's reliability.
* 1920s: Fishing fleets convert to oil engines. Atlas-Imperial of Oakland, Union, and Lister diesels appear.
* 1922: Mack Boring & Parts Company is established.
* 1924: First diesel trucks appear.
* 1928: Canadian National Railway employs a diesel shunter in their yards.
* 1930: Edward McGovern Sr., founder of Mack Boring & Parts Company, opens the first diesel-only engine institute in North America.
* 1930s: Clessie Cummins starts with Dutch diesel engines, and then builds his own into trucks and a Duesenberg luxury car at the Daytona speedway.
* 1930s: Caterpillar starts building diesels for their tractors.
* 1933: Citroën introduced the Rosalie, a passenger car with the world’s first commercially available diesel engine developed with Harry Ricardo.
* 1934: General Motors starts a GM diesel research facility. It builds diesel railroad engines—The Pioneer Zephyr—and goes on to found the General Motors Electro-Motive Division, which becomes important building engines for landing craft and tanks in the Second World War. GM then applies this knowledge to market control with its famous Green Leakers for buses and railroad engines.
* 1934-35: Junkers Motorenwerke in Germany starts production of the Jumo aviation diesel engine "family", the most famous of these being the Jumo 205, of which over 900 examples are produced into the outbreak of World War II.
* 1936: Mercedes-Benz builds the 260D diesel car. AT&SF inaugurates the diesel train Super Chief.
* 1936: Airship Hindenburg is powered by diesel engines.
How diesel engines work
In mechanical terms, the internal construction of a diesel engine is similar to its gasoline counterpart—components such as pistons, connecting rods and a crankshaft are present in both. Like a gasoline engine, a diesel engine may operate on a four-stroke cycle (similar to the gasoline unit's Otto cycle), or a two-stroke cycle, albeit with significant dissimilarity to the gasoline equivalent. In both cases, the principal differences lie in the handling of air and fuel, and the method of ignition.
A diesel engine relies upon compression ignition to burn its fuel, instead of the spark plug used in a gasoline engine. If air is compressed to a high degree, its temperature will increase to a point where fuel will burn upon contact. This principle is used in both four-stroke and two-stroke diesel engines to produce power.
Unlike a gasoline engine, which draws an air/fuel mixture into the cylinder during the intake stroke, the diesel aspirates air alone. Following intake, the cylinder is sealed and the air charge is highly compressed to heat it to the temperature required for ignition. Whereas a gasoline engine's compression ratio is rarely greater than 12:1 to avoid damaging preignition, a diesel's compression ratio is usually between 14:1 and 25:1. This extremely high level of compression causes the air temperature to increase to 700 to 900 degrees Celsius (1300 to 1650 degrees Fahrenheit).
As the piston approaches top dead centre (TDC), fuel oil is injected into the cylinder at high pressure, causing the fuel charge to be nebulized. Owing to the high air temperature in the cylinder, ignition instantly occurs, causing a rapid and considerable increase in cylinder temperature and pressure (generating the characteristic Diesel "knock"). The piston is driven downward with great force, pushing on the connecting rod and turning the crankshaft.
When the piston nears bottom dead centre the spent combustion gases are expelled from the cylinder to prepare for the next cycle. In many cases, the exhaust gases will be used to drive a turbocharger, which will increase the volume of the intake air charge, resulting in cleaner combustion and greater efficiency.
The above sequence generally describes how a diesel operates. However, there are striking differences between the four-stroke and two-stroke versions:
Four-Stroke
The cycle starts with the intake stroke, which begins when the piston is near top dead centre. The intake valve is opened, creating a passage from the exterior of the engine (generally through an air filter assembly), through the intake port in the cylinder head and into the cylinder itself. As the piston moves toward bottom dead centre, a partial vacuum develops, causing air to enter the cylinder. In the case of a turbocharged engine, the air is rammed into the cylinder at higher than atmospheric pressure. As the piston passes through bottom dead centre, the intake valve closes, sealing the cylinder.
The compression stroke begins as the piston passes through bottom dead centre and starts upward. Compression will continue until the piston approaches top dead centre. The energy required for the compression stroke comes from the momentum of a flywheel on the crankshaft as well as (in multi-cylinder engines) other pistons in their power stroke.
The power stroke occurs as the piston reaches top dead centre at the end of the compression stroke. At this time, fuel injection occurs, resulting in combustion and the production of useful work.
The final stroke is the exhaust stroke, which begins as the piston approaches bottom dead centre following ignition. The exhaust valve in the cylinder head is opened and as the piston starts upward, the spent combustion gases are forced out of the cylinder. Near top dead centre the intake valve will start to open before the exhaust valve is fully closed, a condition referred to as valve overlap. Overlap produces a flow of cooling intake air over the exhaust valve, prolonging its life. Following the completion of the exhaust stroke the cycle will begin anew.
Two-Stroke
Intake begins when the piston is near bottom dead centre. Air is admitted to the cylinder through ports in the cylinder wall (there are no intake valves). Since the piston is near bottom dead centre, aspiration due to atmospheric pressure isn't possible. Therefore a mechanical blower or hybrid turbocharger (a turbocharger that is mechanically driven from the crankshaft at low engine speeds) is employed to charge the cylinder with air. In the early phase of intake, the air charge is also used to force out any remaining combustion gases from the previous power stroke, a process referred to as scavenging. As the piston passes through bottom dead centre, the exhaust valve(s) will be closed and, owing to the pressure generated by the blower or turbocharger, the cylinder will be filled with air. Once the piston starts upward, the air intake ports in the cylinder walls will be covered, sealing the cylinder. At this point, compression will commence. Note that exhaust and intake actually occur in one stroke, the period during which the piston is near the bottom of the cylinder.
As the piston rises, compression takes place and near top dead centre, fuel injection will occur, resulting in combustion, driving the piston downward. As the piston moves downward in the cylinder it will reach a point where the exhaust valves will be opened to expel the combustion gases. Continued movement of the piston will expose the air intake ports in the cylinder wall, and the cycle will start anew. Note that the cylinder will fire on each revolution, as opposed to the four-stroke engine, in which the cylinder fires on every other revolution.
Cold weather and diesels
In cold weather, diesel engines can be difficult to start because the mass of the cylinder block and cylinder head absorb the heat of compression, thus preventing ignition. Spark ignition engines undergo the same problem, though they have the added benefit of a spark plug to help cause ignition. The main reason diesel engines take a long time to warm up in cold weather is the lack of a throttle. Spark ignition engines are throttled, so only the right amount of air comes in at a time. This is less efficient, but spark plugs only work near the stoichiometric, or the proper ratio of air to fuel for complete and most efficient combustion, mixture of fuel and air. Diesel engines accept a cylinder full of air and measure in the right amount of fuel. So each time the intake valve on a diesel opens, a full charge of cold air enters the cylinder. This cools the cylinder back down. The heat gained from each combustion process therefore can only cause a gain in temperature that is much, much smaller than it would be in a spark ignition engine.
Some engines use small electric heaters called glow plugs inside the cylinder to help ignite fuel when starting. Some even use resistive grid heaters in the intake manifold to warm the inlet air until the engine reaches operating temperature. Engine block heaters (electric resistive heaters in the engine block) connected to the utility grid are often used when an engine is turned off for extended periods (more than an hour) in cold weather to reduce startup time and engine wear. In the past, a wider variety of cold-start methods were used. Some engines, such as Detroit Diesel engines and Lister-Petter engines, used a system to introduce small amounts of ether into the inlet manifold to start combustion. Sabb marine engines and Field Marshall tractors (amongst others) used slow-burning solid-fuel 'cigarettes' which were fitted into the cylinder head as a primitive glow plug. Lucas developed the 'Thermostart', where an electrical heating element was combined with a small fuel valve. Diesel fuel slowly dripped from the valve onto the hot element and ignited. The flame heated the inlet manifold and when the engine was turned over the flame was drawn into the combustion chamber to start combustion. The most extreme cold-starting system was probably that developed by International Harvester for their WD-40 tractor of the 1930s. This had a 7-litre 4-cylinder engine which ran as a diesel, but was started as a petrol engine. The cylinder head had valves which opened for a portion of the compression stroke to reduce the effective compression ratio, and a magneto produced the spark. An automatic ratchet system automatically disengaged the ignition system and closed the valves once the engine had run for 30 seconds. The operator then switched off the petrol fuel system and opened the throttle on the diesel injection system.
Such systems fell out of favour when electrical glow plug systems proved to be the simplest to operate and produce. Direct-injection systems advanced to the extent that cold-starting systems were not needed and then electronic fuel injection systems rendered most cold-start system unnecessary.
Diesel fuel is also prone to "waxing" or "gelling" in cold weather, terms for the solidification of diesel oil into a partially crystalline state. The crystals build up in the fuel (especially in fuel filters), eventually starving the engine of fuel and causing it to stop running. Low-output electric heaters in fuel tanks and around fuel lines are used to solve this problem. Also, most engines have a "spill return" system, by which any excess fuel from the injector pump and injectors is returned to the fuel tank. Once the engine has warmed, returning warm fuel prevents waxing in the tank. Fuel technology has improved so that with special additives waxing rarely occurs in all but the coldest weather.
A vital component of all diesel engines is a mechanical or electronic governor, which limits the speed of the engine by controlling the rate of fuel delivery. Unlike Otto-cycle engines, incoming air is not throttled and a diesel engine without a governor can easily overspeed, resulting in its destruction. Mechanically governed fuel injection systems are driven by the engine's gear train. These systems use a combination of springs and weights to control fuel delivery relative to both load and speed. Modern, electronically controlled diesel engines control fuel delivery and limit the maximum rpm by use of an electronic control module (ECM) or electronic control unit (ECU). The ECM/ECU receives an engine speed signal, as well as other operating parameters such as intake manifold pressure and fuel temperature, from a sensor and controls the amount of fuel and start of injection timing through electric or hydraulic actuators to maximize power and efficiency and minimize emissions.
Controlling the timing of the start of injection of fuel into the cylinder is a key to minimizing emissions, and maximizing fuel economy (efficiency), of the engine. The timing is usually measured in units of crank angle of the piston before top dead centre. For example, if the ECM/ECU initiates fuel injection when the piston is 10 degrees before TDC, the start of injection, or timing, is said to be 10° BTDC. Optimal timing will depend on the engine design as well as its speed and load.
Advancing the start of injection (injecting before the piston reaches TDC) results in higher in-cylinder pressure and temperature, and higher efficiency, but also results in elevated engine noise and increased oxides of nitrogen (NOx) emissions due to higher combustion temperatures. On the other hand, delayed start of injection causes incomplete combustion, reduced fuel efficiency and an increase in black exhaust smoke, containing a considerable amount of particulate matter (PM) and unburned hydrocarbons (HC).
Early fuel injection systems
The modern diesel engine is a combination of two inventors' creations. In all major aspects, it holds true to Rudolf Diesel's original design, that of igniting fuel by compression at an extremely high pressure within the cylinder. However, nearly all present-day diesel engines use the so-called solid injection system invented by Herbert Akroyd Stuart for his hot bulb engine (a compression-ignition engine that precedes the diesel engine and operates slightly differently). Solid injection raises the fuel to extreme pressures by mechanical pumps and delivers it to the combustion chamber by pressure-activated injectors in an almost solid-state jet. Diesel's original engine injected fuel with the assistance of compressed air, which atomized the fuel and forced it into the engine through a nozzle (a similar principle to an aerosol spray). This is called an air-blast injection. The size of the gas compressor needed to power such a system made early diesel engines very heavy and large for their power outputs, and the need to drive a compressor lowered power output even more. Early marine diesels often had smaller auxiliary engines whose sole purpose was to drive the compressors to supply air to the main engine's injector system. Such a system was too bulky and inefficient to be used for road-going automotive vehicles.
Solid injection systems are lighter, simpler, and allow for much higher speed, and so are universally used for automotive diesel engines. Air-blast systems provide very efficient combustion under low-speed, high-load conditions, especially when running on poor-quality fuels, so some large marine engines use this injection method. Air-blast injection also raises the fuel temperature during the injection process, so is sometimes known as hot-fuel injection. In contrast, solid injection is sometimes called cold-fuel injection.
The vast majority of diesel engines in service today use solid injection and the information below relates to that system. In the diesel engine, only air is introduced into the combustion chamber. The air is then compressed to about 600 pounds per square inch (41 bar), compared to about 200 pounds per square inch (14 bar) in the gasoline engine. This high compression heats the air to about 1,000 °F (538 °C). At this moment, fuel is injected directly into the compressed air. The fuel is ignited by the heat, causing a rapid expansion of gases that drive the piston downward, supplying power to the crankshaft. In Diesel's manuals, he described the supply of compressed gas into the cylinder to promote the final burn.
Advantages of the diesel engine are numerous. It burns considerably less fuel than a gasoline engine performing the same work. It has no ignition system to attend to. It can deliver much more of its rated power on a continuous basis than can a gasoline engine. The life of a diesel engine is generally longer than a gasoline engine. Although diesel fuel will burn in open air, it will not explode unless compressed.
Some disadvantages to diesel engines are that they are very heavy for the power they produce due to the required heavy design, and their initial cost is much higher than a comparable gasoline engine.
Mechanical and electronic injection
Older engines make use of a mechanical fuel pump and valve assembly that is driven by the engine crankshaft, usually from the timing belt or chain. These engines use simple injectors that are basically very precise spring-loaded valves that open and close at a specific fuel pressure. The pump assembly consists of a pump that pressurizes the fuel and a disc-shaped valve that rotates at half crankshaft speed. The valve has a single aperture to the pressurized fuel on one side, and one aperture for each injector on the other. As the engine turns, the valve discs will line up and deliver a burst of pressurized fuel to the injector at the cylinder about to enter its power stroke. The injector valve is forced open by the fuel pressure, and the diesel is injected until the valve rotates out of alignment and the fuel pressure to that injector is cut off. Engine speed is controlled by a third disc, which rotates only a few degrees and is controlled by the throttle lever. This disc alters the width of the aperture through which the fuel passes, and therefore how long the injectors are held open before the fuel supply is cut, which controls the amount of fuel injected.
This contrasts with the more modern method of having a separate fuel pump which supplies fuel constantly at high pressure to each injector. Each injector has a solenoid, is operated by an electronic control unit, which enables more accurate control of injector opening times that depend on other control conditions, such as engine speed and loading, resulting in better engine performance and fuel economy. This design is also mechanically simpler than the combined pump and valve design, making it generally more reliable, and less noisy, than its mechanical counterpart.
Both mechanical and electronic injection systems can be used in either direct or indirect injection configurations.
Older diesel engines with mechanical injection pumps could be inadvertently run in reverse, albeit very inefficiently, as witnessed by massive amounts of soot being ejected from the air intake. This was often a consequence of push starting a vehicle using the wrong gear.
Indirect injection
An indirect injection diesel engine delivers fuel into a chamber off the combustion chamber, called a prechamber or ante-chamber, where combustion begins and then spreads into the main combustion chamber, assisted by turbulence created in the chamber. This system allows for a smoother, quieter running engine, and because combustion is assisted by turbulence, injector pressures can be lower, which in the days of mechanical injection systems allowed high-speed running suitable for road vehicles (typically up to speeds of around 4,000 rpm). The prechamber had the disadvantage of increasing heat loss to the engine's cooling system, and restricting the combustion burn, which reduced the efficiency by 5% – 10%. Indirect injection engines were used in small-capacity, high-speed diesel engines in automotive, marine and construction uses from the 1950s, until direct injection technology advanced in the 1980s. Indirect injection engines are cheaper to build and it is easier to produce smooth, quiet-running vehicles with a simple mechanical system. In road-going vehicles most prefer the greater efficiency and better controlled emission levels of direct injection.
