Advanced Automotive Powertrain Concepts

In this article, I will be looking into climate change, technological solutions to climate change, technological solutions to climate change, advanced internal combustion engine technology (ICE), hybrid technology such as micro, full, series, parallel and plugin, the carbon dioxide 'well-to-wheel' analysis, biofuels both alcohol and bio-diesel, engine downsizing, hydrogen powertrains, hydrogen fuel cells, a timeline of the future for powertrains, transmissions, mass market technology and a glimmer of hope for the future . Please feel free to skip to the parts most relevant to you.


Climate Change 

As already mentioned in an article about the automotive legislative constraints on emissions, noise and safety, there are warning signs that if we continue 'business as normal' now, the carbon dioxide levels will hit 1000ppm where it needs to be maintained at 450ppm to achieve climate change to acceptable levels. This makes it clear that the future powertrains must produce less carbon dioxide and be more efficient in general.


Technological Solutions

To the problem of climate change, the automotive sector has a few solutions it is setting out:
  • Vehicle technologies - To improve efficiency, cars can be made from lightweight materials, have improved aerodynamics and reduced rolling resistance.
  • Powertrain - There are future powertrains such as advanced gasoline/diesel engines, hybrid (micro start/stop, full, series, parallel or plugin), hydrogen and fuel cell engines using biofuels, electricity, hydrogen internal combustion engines or fuel cells.

Advanced ICE Technology

There have been many improvements to both gasoline and diesel internal combustion engines over the years which have lead to more efficient engines producing less carbon dioxide:
  • Gasoline engines have advanced direct injection which measures the amount of petrol needed into the combustion chamber for stoichiometric ignition. This has led to a 10% fuel economy improvement.
  • Advanced diesel engines have higher pressure common rail diesel fuel injection, up to 2000 bar, which improves fuel economy and emissions.
  • Engines are being downsized and being integrated with a turbo or a supercharger.
  • The manufacturing technology and the product itself are mature in the market and constantly being innovated upon.
  • New NOx after treatment is required for emissions legislation.
  • There is a trend to reduce the particulate levels for both petrol and diesel engines.
  • Saying this, there are always conflicts between reducing carbon dioxide and NOx levels.


Hybrid Technologies

Hybrids are becoming ever more popular because they are cleaner on the environment and much more fuel economical as compared to the typical ICE. There are many different types of hybrid systems:

  • Micro hybrid - This involves a conventional IC engine with a heavy duty smart start system. The engine stops everytime the wheels stop rotating and starts instantaneously as the accelerator pedal is pressed. For this reason, slightly large battery capacities are needed. Stop/start technology helps improve fuel economy mainly around town where vehicles are stopping at traffic lights etc.
  • Full hybrid series - The IC engine drives the electric generator which provides the power to the electric motors which drives the wheels. The IC engine is in no way powering the wheels directly.
  • Full hybrid parallel - This involves an IC engine in parallel with an electric motor/s that drives through transmission so that either power source can drive the wheels through the gearbox. This requires a significantly larger battery.
  • Plugin hybrid - This is the same as a full hybrid parallel with/without an IC engine that has the ability to charge the battery from mains electricity. 

Plugin Hybrid Opportunities

Plugin hybrid vehicles are useful to utilise the surplus base load electricity during overnight charging and can often lead to much cheaper electricity rates too. Hybrid vehicles may be a major contribution for urban/city centre commuter vehicles.
However, there needs to be some improvements in battery performance to delivery a good range, low cost and a high cycle life. At the moment lithium ion (Li-Ion) batteries are being used which need precise charge control but do have a high energy density.

  • Hybrids provide one potential bridge to the next dominant powertrain and every manor manufacturer should offer a solution.
  • It is already a sizeable niche market opportunity but is not a wholesale migration to hybrid technology.
  • Hybrid demand is difficult to predict since is depends on the incremental cost mitigation, emissions based taxation, congestion/pollution charges and market and consumer reaction. In 2010, it is lses than 3% of total sales of vehicles which is still a significant opportunity.
There are a few wider due to the fact that hybrids come with trade-offs to be managed:
  • Recyclability - batteries and new constraints.
  • Safety of the new package constraints in a crash as well as the electrical integrity issues.
  • Weight of the additional vehicle systems.
  • Packaging of the new systems to maintain usability.
  • Customer acceptance for the usability and familiarity with the technology,

Hybrid Summary

Hybrid vehicles are...
  • ...an interim solution improving emissions.
  • ...an attractive market proposition.
  • ...an exciting technical challenge.
  • ...a stepping stone to the next dominant powertrain technology (alternative fuel engines, fuel cells and hydrogen internal combustion engines).
  • ...a positive industry response to climate change.
But, it is not the single solution to the climate change challenge with multiple technologies continuing to emerge to meet complex market fragmentation needs. 

Additional Technologies

  • Biofuels/hydrogen
  • Engine downsizing
  • Turbo and supercharging
  • Flywheel hybrids such as Flybrid - This combines a flywheel with an electric motor for energy recovery and reuses it by charging the battery pack or supercapacitors. This does add weight byt is a much simpler control strategy than mechanical systems.
  • Electric vehicles with advanced batteries - These include vehicles such as the Nissan Leaf with a price of £23,990 including the £5,000 electric vehicle Government incentive. It has a range of 100 miles cruising without the air conditioning or heater on and uses a laminated Lithium Ion battery. This type of battery has a limited life and are expensive to replace. Therefore, there are some serious concerns about the depreciation of electric vehicles. This is why some electric vehicles such as the Renault Twizy have a hire for the batteries at £45/month.
  • Regenerative braking
  • Consumer behaviour, driver education and road congestion management

Carbon Dioxide 'Well-to-Wheel' Analysis

The below analysis makes clear the amount of g/km in carbon dioxide each of the most major powertrains consume. For gasoline and diesel, the majority if done by the consumer with a litle done in transporting the fuel to fuel stations. Hybrid is not as efficient as people would have thought since the electricity produced for hybrids usually comes from coal power stations that pump out tons of carbon dioxide. Bio-ethanol is a good alternative for combating climate change since the fuel is produced by plants which take COout of the air (and then the consumer puts it back into the air). However, the main problem with this is that there is simply not enough space to grow enough biofuels to meet consumer needs (if there was, we couldn't because land needs to be used to grow food). Hydrogen fuel cells, again, are actually quite high in carbon dioxide levels because of how the electricity is generated. Therefore, it is only renewable electricity combined with hydrogen fuel cells that produce the lowest carbon dioxide levels of around 35g/km. Saying this, the biggest areas we can improve is with the gas, diesel and hybrid systems as well as how we produce the electricity from power stations.
Carbon dioxide (CO2) levels for different powertrains

Biofuels - Alcohol /Bio-Diesel

As mentioned above, biofuels appear to be a virtuous solution. They have huge environmental benefits and low carbon dioxide levels. As of 2010, 5% of transport fuel has to be renewable. 
The problem is simply that there is not enough land mass for a major contribution. Already, 50% of USA grain production is committed to biofuel and, because of this, food prices are rising. This causes those least able to feed themselves to be hit hardest by biofuel production.

However, there is hope. Gasoline replacement for a proportion of petroleum fuel using ethanol is produced from 2nd or 3rd generation biofuel. This utilises the waste cellulosic material from agriculture or wood products to make E85 ethanol. There are already some bio-diesel and aviation fuels that are made from organic oils suh as rape seed and maize. 

But, there is insufficient land mass to fully replace all fossil fuels for transport. There are huge technical issues to overcome moving beyond the current 5% biofuel usage in existing engine technology.


Engine Downsizing

All manufactured are working on smaller lighter engines with higher specific power outputs. Examples include the Ford 1.0 litre 3 cylinder Ecoboost 100-200PS, Jaguar Limo-Green project, Lotus 3 cylinder engine which is being developed with several manufacturers in combination with series hybrids and the Ford Ecoboost 2.0 Direct Injection Petrol Turbo.


Hydrogen Powertrains

Hydrogen is a new emerging market for future powertrains:
  • It is an energy vector - Hydrogen is not an energy source in the sense that it does not occur naturally.
  • It would prove useful it produced from renewable sources. If major renewable infrastructures are constructed, this could prove to be a long term solution.
  • It is a good solution to deliver zero emissions in urban environments.
However, there are some problems with hydrogen powertrains too:
  • Hydrogen has a low energy density which limits its transportation range.
  • The storage and distribution of hydrogen has proved to be challenging.
  • To store liquid hydrogen at -253 degrees Celsius has proved to be even more challenging.
  • Hydrogen powertrains are not beneficial is the hydrogen is harvested from the power produced by fossil fuel energy.
  • Hydrogen fuel cells are extremely expensive, with a high volume fuel tank costing an estimated $12,500/unit.
  • If liquid hydrogen is to be used, the transportation is of the liquid is a problem as in order to keep it as a liquid, some of the hydrogen needs to evaporate off to keep the rest at the low temperature. An experiment to make 36 buses in 12 cities around the world for 27 months hydrogen fuel cells was created. The liquid hydrogen was supplied from Holland. Although 45 tonnes of the liquid hydrogen was produced, only 18 tonnes made it to fuel the buses.

Hydrogen Fuel Cells

Hydrogen fuel cells work by converting hydrogen and oxygen (from the atmosphere) into electricity which forms water as the waste product. It reverses the process of electrolysis of water when splitting into hydrogen and oxygen using electricity.


Timeline of Powertrain

With all this talk of future and current powertrains, how long can we expect to see each technology last or enter into the consumer market?
  • Advanced gasoline internal combustion engines  - Another 30+ years because they are low cost, reliable, familiar and there is already existing capital and refuelling infrastructures.
  • Modern clean diesel internal combustion engines - Another 40+ years because diesels are generally more fuel efficient and there are some essential challenges to overcome such as fuel quality and emissions.
  • Hybrid powertrains - Will become 10-15% of the market because they are beneficial in urban areas and can be combined with advanced fuel powertrains.
  • Hydrogen internal combustion engines - A bridging technology. The emissions of such engines have been realised in the long term. Therefore, you can expect for this area of powertrain to increase in funding and popularity to improve transport emissions.
  • Fuel cells - Impact in 20-30 years. This is the endgame for the hydrogen economy and is the most environmentally neutral powertrain to date.

Transmissions

  • There are trends to increase the number of manual ratios since this will help improve fuel economy.
  • 5 speed gearboxes are the standard at the moment but will move to 6 speed.
  • Automatics will have increased gears too, ranging from 5 - 8 gears for improve fuel economy.
  • Auto shift manuals will increase to improve fuel economy with refinement matching automatics.
  • There will be an increased trend to DSG (direct shift gearbox).

It's all about Affordable Mass Market Technology

To achieve 70h/km COcars will need all of the following technologies:
  • Light weight materials
  • Reduced frontal area for reduced drag
  • Aerodynamic aids
  • Rolling resistance reductions
  • Smaller turbo/supercharged engines
  • Hybrid technology
  • Regenerative braking
  • Bio-fuels/improves fossil fuels
...and still appeal to the consumers. There will be far more powertrain technology alternatives tailored to customer usage in future vehicles than in the past. COemissions and climate change are a total systems issue and not solely the responsibility of vehicle manufacturers. Heavy commercial vehicles and buses will use similar technology to those found in cars but the COchallenge will be even more difficult.


A Glimmer of Hope

It is not all bad news! Here is a glimmer of hope:
  • The sunlight which hits the Earth every hour is sufficient to meet all of man's energy needs for a whole year.
  • Basic scientific research is needed to efficiently capture solar energy.
  • Solar power could provide plentiful hydrogen at low cost.
  • The catalyst technology is not mature.
  • Artificial photosynthesis
  • It is true we need fundamental chemistry breakthroughs which is all probably around 50 years away.