Turbocharging - fuel efficiency and the path to EV's

Contributor: Peter Els
Posted: 03/14/2017
Rate this Article: 
Average: 4 (1 vote)

EU emission targets have driven significant changes to drivetrain technology in the automotive industry over the last 20 years. Demands for reduced CO2 and NOx pollution have led OEMs to invest in a range of technologies such as turbocharging and downsized engines to meet ever more stringent directives. However, in light of the VW diesel scandal and improved test cycles due for implementation in the coming years, even more efficiency gains are required, and it remains to be seen which technologies will prove effective in the long term.

In general terms the automotive sector has been ‘on the path’ to electrification for some time, but the electric vehicle revolution that some predicted has failed to materialize as of yet. The EV and Hybrid markets do continue to make ground, though, and increasing investment tied to rapidly improving technology suggests that more growth is on the horizon.

The ultimate aim, of course, is to improve fuel efficiency to reduce emissions, and to that end turbocharging has been a key technology. Very few manufacturers still offer naturally aspirated engines in passenger cars, and we have seen a continual trend of downsizing engines and incorporating turbochargers to boost power. The benefits of such technologies may have been overestimated by the automotive industry, and ‘real world’ emissions have been found to exceed quoted figures quite substantially.

The industry has to react, and there are already signals that the next decade may see OEMs move in a different direction, both in terms of engine sizing and electric and hybrid drivetrains.

Legislation Driving Growth

EU regulations demand that new cars sold after 2015 in the European Union emit no more that 130 g CO2/km - equivalent to approximately 5.6 l/100 km of petrol or 4.9 l/100 km of diesel. By 2021 this limit will be reduced to 95 grams of CO2 per kilometer, with a phase in period from 2020.

To this end both the EU and the automotive industry pushed diesel technology as an answer to the emission problem, as diesel engines emit around 15% less CO2 compared to petrol engines. Tax breaks on diesel engines and better fuel efficiency fueled growth in the sector, and much of the EU vehicle market is still dominated by diesel engines.

To meet emission targets, manufacturers have introduced various technologies including exhaust gas recirculation and selective catalytic reduction, and a significant trend has been to downsize engines and fit them with turbochargers for increased power.

The official testing procedure in place in Europe is the NEDC which will remain in place until 2019, but from 2017 onwards the Worldwide Harmonized Light Vehicles Test Procedure (WLTP) will run parallel while it is being introduced and targets are translated between the test procedures.

Targets are applied to a fleet of vehicles, and electric vehicles have counted as 0 g/km towards fleet averages, while cars that emit less than 50 g/km CO2 on NEDC test cycles have been eligible for super credits to aid overall compliance with the limits. Such credits are due to be reintroduced for a second phase from 2020 as new targets are implemented. The EU Parliament has proposed a 2025 target in the range of 68-78 g/km CO2 - with a review and impact assessment due to take place in 2017.

Turbocharging and Downsizing

One of the most vital technologies in reducing emissions has been turbocharging, and three-cylinder engines with a 1 liter or lower capacity have become commonplace in small compact vehicles. Europe has been the leader in the adoption of turbocharging technology, and a look at key supplier Honeywell’s predictions for the turbo market in its 2015 annual report demonstrate a level of confidence within the motor industry.

  • Adoption of turbocharged 3-cylinder and 4-cylinder gasoline and diesel engines is emerging as a huge growth trend globally for fuel efficient entry-level and mid-range vehicles. Honeywell sees an industry compound average growth rate (CAGR) of 30 percent through 2020 resulting in sales of seven million 3-cylinder turbocharged engines by 2020.
  • Globally, 4-cylinder engines will continue to represent 75 percent of the turbocharged light vehicle industry in 2020. Honeywell forecasts this turbo engine family will have a seven percent CAGR through 2020.
  • By 2020 more than two million light new vehicles per year will be launched with multi-stage boosting systems.
  • Globally, diesel engines will continue to be an important share of light vehicle sales at nearly 20 percent, due to their lower fuel consumption and CO2 emissions.
  • Penetration of hybrid powertrains, including ‘plug-ins’, will be up four points to seven percent of the global light vehicle market. Approximately 25 percent of these vehicles will use turbocharged engines, compared to ten percent today, opening the door to potential future enhancement with electric boosting and energy recovery.

Developments in the interim, however, may adversely affect the trend of downsizing, and there are signs that OEMs may move away from the concept of ever smaller engines.

New Regulations Leading to New Trends

The issue - which has rarely been out of the news this year - is in the test standards. The NEDC has been shown to give an inaccurate representation of real world driving conditions, and therefore emissions, and the new WLTP procedures will give a far more accurate picture of emissions - particularly NOx emissions.

In 2012 the World Health Organisation (WHO) reclassified diesel engine exhaust from ‘probably carcinogenic’ to ’carcinogenic’, and NOx emissions are increasingly coming under the microscope. As diesel vehicles emit around four times the NOx emissions of gasoline engines, the tightening of global regulations will hugely affect the European market which is heavily penetrated by diesel vehicles in comparison to the US and Asian markets. However, starting in 2017 all new cars will be subject to realistic ‘on-road’ testing, and all new models must comply by 2019.

The Euro IV 2015 targets for NOx emissions from diesel vehicles stood at 80 mg/km, but it has become clear that although manufacturers could meet these targets in NEDC test cycles, they are some way off in real driving conditions. The International Council of Clean Transport (ICCT), which was central to the diesel emissions scandal, said in a report that technologies exist to control both CO2 and NOx emissions and are being deployed by manufacturers, but that a “high conformity factor is indicative of poor emissions performance”.

The EU has proposed factors of 2.1 for 2019 and 1.5 for 2021 in respect of the initial Euro IV target - a move designed to assist manufacturers as they adjust to new regulations and test cycles, but one which has angered environmental campaigners.

A report by Reuters suggests that OEMs may be ready to move away from smaller engines as they continue to meet the regulatory challenges. GM, says Reuters, will not replace its 1.2 liter diesel when the engines are updated to a new architecture in 2019. VW has said it will replace its 1.4 liter three-cylinder engine with a 1.6 liter four-cylinder model for cars such as the Polo, and Renault is planning to enlarge its 1.6 liter R9M diesel engine - which had previously replaced a 1.9 liter model in 2011.

VW has also given a clear indication of its direction of travel this year, by committing to its ‘Strategy 2025’ vision, whereby the car-maker aims to sell between two to three million electric vehicles annually by 2025.

Electric Vehicle Market Development

It appears that the industry is ready for the widespread adoption of electric vehicles, but with several challenges on that particular path the interim period will be one of a mixture of technologies to. Cost and range of batteries, charging infrastructure and performance are hurdles to overcome, and many are predicting a rapid growth in hybrid technology in the coming years.

Globally the electric vehicle market passed the landmark of two million plug-in EVs on the road by the end of 2016, and some experts are tentatively suggesting the revolution is finally underway. Sales of electric vehicles reached a 1 % market share in Europe in 2015, and the total number of EVs on the road in the EU now stands around the 500,000 mark.

The growth of electric and plug-in hybrid vehicles is difficult to quantify, and several interesting estimates have been made by various interested parties. Large component supplier Schaeffler Technologies AG & Co of Germany predicts that by 2030 around 38% of global vehicles will be hybrids, with 10 % pure electric vehicles. Another supplier to the industry, GKN, suggests that 20 % of all vehicles will be electric by 2030, and 25 % will be hybrids. In the shorter term most estimates center on a market penetration figure of 5 % for EVs by 2025, although VW are aiming for a huge 25 % of its vehicle sales, while Mercedes expects EVs to make up 15-20 % of its sales by 2025.


As ever in the auto industry, there are several factors to consider in terms of meeting the challenges of reduced emissions. Lightweighting, downsizing and turbocharging have made significant contributions to fuel efficiency gains, but as a concept, downsizing may have reached its limits. Turbocharging will continue to be a significant technology as a bridge towards hybrid and electric powertrains, but it will be in conjunction with the increasing use of exhaust gas control technologies to meet new test standards. In the near future ‘downsizing’ may consist of taking a smaller engine and adding an electric motor, as hybrid technologies come to the fore.

Peter Els
Contributor: Peter Els