Turbochargers and superchargers are often spoken about in the same breath and whilst there are similarities between the two devices there are also some key differences with regards their use in passenger vehicles.

Both technologies fall into the category of forced induction systems, which enable a vehicle’s engine to produce more power than an equivalent ‘normally aspirated’ engine. This is achieved by compressing the density of air within the fuel/air mix prior to its ignition within the engine’s cylinders. This creates a considerable amount of boost, which can provide up to 50% more power into the engine.

Although they share the same forced induction concept, how the air compression components are powered is the main difference between the two. A supercharger is driven from the engine’s crankshaft by a belt, shaft or chain whereas turbochargers obtain their power from a turbine which harvests energy from the engine’s exhaust gases.

Turbochargers

In simple terms a turbo is an air pump that enables more air to be pumped into the engine at higher pressure. This replicates the effect of having a larger cylinder but with more efficiency. The turbo is made up of two distinct sections; the compressor end and the turbine end. The compressor end (or cold end) is often made from aluminium and experiences temperatures of up to 70°C. Ambient air is drawn into the compressor housing and a compressor wheel compresses the air and accelerates it to very high speeds.

The turbine end (or hot end), is made from cast iron or stainless steel and can reach temperatures of up to 960°C, as the exhaust gases rotate the turbine wheel at speeds of up to 280,000 rpm.  The turbine housing directs exhaust gas from the engine onto the turbine wheel blades, and once it has passed through the turbine wheel, the gas then passes out through the exhaust system as with normally aspirated vehicles.

Once the combustion process starts, this creates a continuous cycle and the turbo makes use of waste energy from the exhaust gases. More air in the cylinder also enables more fuel flow through to the cylinder and therefore achieves more power.

Superchargers

As mentioned above a supercharger is mechanically driven by the engine and increases the amount of air through intake by compressing the air above atmospheric pressure, without creating a vacuum. This forces more air into the engine, providing a boost, which in turn allows more fuel to be added to the charge, and therefore increases the power of the engine. There are two main types of superchargers. Positive Displacement superchargers produce a fixed amount of pressure that doesn’t increase much as the engine increases its RPM. Dynamic Compressors, as the name suggest, produce more pressure as the engine’s RPM increases.

Comparing Turbochargers v Superchargers

Besides how the two devices work (explained above) another key difference is that whilst a supercharger requires engine power to run, a turbocharger runs off waste (exhaust) energy created by the engine. This means that overall turbochargers operate with higher efficiency, utilising exhaust energy which is typically lost in naturally-aspirated and supercharged engines.

Turbochargers provide significantly increased horsepower for engines, especially allowing smaller engines to produce much more power in relation to their size, whilst simultaneously offering better fuel economy. On the other hand, turbochargers tend to provide less boost at lower engine RPMs whilst the turbo spools up; the so called turbo lag.

Superchargers also increase engine horsepower and because they are driven by the engine’s crankshaft, provides good power at low engine RPM without any lag. The trade-off is reduced efficiency, given superchargers use engine power to produce engine power.

The reason why turbochargers are used most commonly in Europe is because the engines are small and four cylinders are standard. Superchargers can deliver their boost at lower RPMs then a turbocharger, whereas the turbocharger works best at high engine speeds. Turbochargers are quieter and superchargers are more reliable. Superchargers are easier to maintain than the complex turbocharger.

In conclusion when you compare superchargers to turbochargers, there is no clear winner. Which option is better depends on the vehicle itself and how it is typically used. As vehicle technology evolves there will always be demand for both as manufacturers and customers search for power and fuel economy efficiencies.

 

‘Machined from Solid’ compressor wheels are the latest in a long line of developments from the OEMs to enter the aftermarket. Here we explore the evolution of the compressor wheel to determine if there are any benefits to using MFS wheels on standard cast wheel applications.
Continue reading “Cast vs MFS Compressor Wheels”

A year on from the Volkswagen emission scandal, speculation is growing about the life-span of diesel engines, fuelled by rumours that Norway is planning to ban all diesel engine passenger cars by 2025 – with other European countries potentially following suit. So do diesel passenger cars have a future? And how realistic is it to carry out such schemes? What impact will the elimination of diesel passenger cars have on the turbo aftermarket?

CO₂ emissions impact the atmosphere and are continuously reported as a key contributor to climate change. The more recent focus on passenger car emissions has been accelerated by the Volkswagen scandal of 2015. The aftermath revealed there was a huge difference between the results of OEM laboratory tests and real-world driving emissions.

As a result, New European Drive Cycle (NEDC) legislation has been revised in line with real-world driving conditions. This has highlighted that European institutions are trying to get a better understanding of emissions from diesel and petrol  cars.

Improving air quality

In a bid to improve air quality in Norway, leading political parties have called for a ban of the sale of all diesel passenger cars by 2025. In contrast, the UK government has set policies in place to push low emission vehicles – which includes diesel passenger cars. It would be much more difficult to implement an outright ban in the UK. The population is considerably larger, with a larger diesel passenger car parc.

Despite a push on low emission vehicles, air pollution remains a hot topic in the UK. As the country prepares to leave the European Union there needs to be clarity on what is going to happen to current air pollution policies.  When the government pushed diesel cars in the early 2000’s, they knew there would be a negative effect on air pollution. But, they believed it would be vastly outweighed by the reduction in greenhouse gas emissions.

As technology advances, zero air pollution and zero emissions should, in hindsight, become easier to achieve. The current political focus appears to be on rectifying the current situation through the regulation of existing technology such as diesel particulate filters (DPF) or selective catalyst reduction (SCR) technology.

Benefits

There are many benefits to diesel engines. It has been well publicised that today’s diesel passenger cars are the cleanest ever, with high tech filters capturing 99% of particulates. Since the introduction of the Euro emission regulations in 1992 diesel particulate matter has reduced significantly and is currently at the same level as petrol applications at 0.005 g/km. NOx emissions have also significantly reduced and are just 0.02 grams behind petrol passenger cars.

Overall, diesel engines are more efficient to run and contain more energy per litre than petrol engines. Diesels have led the way in turbocharger technology, with petrol applications now quickly following suit. Despite these positives, the Norwegian national parliaments are committed to the ban of diesel passenger cars. They currently lead the way in electric vehicle sales due to tax exemptions, free charging points and parking benefits.

The ‘demonisation’ of diesel

Since the Volkswagen scandal diesel passenger car sales have seen a downward trend; the Group’s Audi division has seen their market share drop from 69% to 67% in the first four months of 2016. Consumer research suggests the scandal has been a major contributing factor in this downturn. Buyers are seeking out petrol applications that match the performance and fuel efficiency of their diesel counterparts, as well as hybrid and electric vehicles.

Although diesel is often in the firing line, it isn’t just these cars that create the problems; it extends to vans, buses, taxis and petrol engines too. For example, diesel road traffic is responsible for about 40 per cent of London’s NOX emissions. Government policies to reduce carbon emissions have indirectly promoted and incentivised the use of diesel over petrol. Which as lead to an increase in the number of diesel cars on the road.

With this in mind, countries calling for a ban of diesel cars need to consider other contributors to vehicle air pollution which are varied. Any new policies should consider the impact to these groups and the effect they will have on the automotive industry as a whole.

In terms of the turbo aftermarket, there are still plenty of turbochargers that will need repair. Due to the adoption of turbos on petrol applications, this will continue for many years to come.

As the global car industry faces increased scrutiny following the Volkswagen emission scandal, there is no doubt that this revelation will have an impact on our market and the future of diesel, but to what extent?

Volkswagen has admitted that it circumvented the emissions control system in over 480,000 2.0-liter diesel vehicles sold in the United States since 2008, to meet strict NOx emission test regulations.

Euro Emission Standards

European emission standards define the acceptable limits for exhaust emissions of new vehicles sold in EU member states and were first introduced in 1992.

Euro 1 (July 1992)  Initiated the switch to unleaded petrol and the universal fitting of catalytic converters to petrol cars to reduce carbon monoxide (CO).

Euro 2 (January 1996)  Further reduced the limit for CO emissions and introduced different emissions limits for diesel and petrol vehicles.

Euro 3 (January 2000)  Added a separate NOx limit for diesel engines and introduced separate Hydrocarbon (HC) and NOx limits for petrol engines.

Euro 4 (January 2005)  Concentrated on cleaning up emissions from diesel cars, reducing particulate matter (PM) and oxides of nitrogen (NOx). Some Euro 4 diesel cars were fitted with particulate filters.

Euro 5 (September 2009)  Tightened the limits on particulate emissions from diesel engines and all diesel cars needed particulate filters to meet the new requirements. For the first time, a particulates limit was set for petrol engines.

Euro 6 (September 2015)  Imposed a significant reduction in NOx emissions from diesel engines (a 67% reduction compared to Euro 5). Also established similar standards for petrol and diesel.

Overall, since Euro 1, PM levels have been reduced by 96% and NOx levels by 87%. To achieve this, new technologies have been developed and adapted to fit vehicle exhaust systems.

Emission Reducing Technologies

Catalytic converters, originally launched in the 1970’s, were designed to clean up CO and HC particulates released as part of the engine combustion process. They react to temperature, converting CO and HC to Carbon Dioxide and water. The reaction depends upon a certain temperature being achieved so they do not work as efficiently in colder
climates.

DPF’s were introduced from January 2005 where diesel particulate levels were reduced to extremely low levels. This reduces the allowable size of PM released to the atmosphere. Reducing the size of PM from the combustion process to this level was not technically possible. This meant all diesel vehicles after September 2009 were fitted with a filter to capture soot and other harmful particles, preventing them entering the atmosphere. A DPF can remove around 85% of the particulates from the exhaust.

To tackle the reduction of NOx, Selective Catalytic Reduction (SCR) systems were introduced in 2010. The SCR system is where Urea (AdBlue) is injected into the exhaust post combustion. In the exhaust, the fluid is converted into ammonia (NH3) which reacts with the NOx in the ‘NOx accumulator,’ breaking the chemical bond and converting NOx into Nitrogen and water. SCR technology alone can achieve NOx reductions by up to 90%, and is one of the most cost-effective and fuel-efficient technologies available to help reduce diesel engine emissions. However, in real world driving conditions, the SCR systems do not work as efficiently and can produce much higher emissions when compared to laboratory testing conditions.

Not over yet…

When the emission levels were set, most engine manufacturers didn’t believe that they were achievable in the set time frames. In the absence of revised levels, the manufacturers have made great progress developing the new DPF and SCR systems. However, the method for testing and proving that the systems do actually achieve the set levels have been flawed; this has allowed manufacturers to achieve the correct levels in lab conditions. But, these do not relate to the actual emissions produced in real world driving conditions. This is now at the heart of the VW scandal.

Find out more about what’s going on in the industry…

 

Parts Design Improvements -There has been much discussion within the automotive repair industry about the differences between using OEM parts and the aftermarket equivalent repair parts. In this article, with a focus on turbochargers; we explore the benefits associated with using high quality repair parts and why such parts can actually improve a turbo repair.   Continue reading “Melett Parts Design Improvements – Better than OE?”