By Professor Roy Douglas, CTO and Co-Founder CATAGEN

Hybrid cars (HEVs) are becoming a popular alternative to conventional petrol and diesel cars as many of us still struggle to take the big step towards full battery electric cars (BEVs).  HEVs offer better fuel economy and hence lower running costs while making us feel that we are doing our bit to save the planet by reducing our emissions footprint.  The key contribution is better fuel consumption and hence lower carbon emissions.  But the big question is how much?

Let’s take a typical family car as an example.  This car, with a diesel engine, will return about 45mpg (6.2 l/100km) on average and about 40mpg for inner city driving, and the petrol version about 30mpg (9.4 l/100km) with 24mpg inner city.   In a similar hybrid (HEV), there are 3 main feature that contribute to savings in fuel consumption:

1.     Start/stop technology allows the engine to be stopped when the car is stationary and improves fuel economy by about 3mpg (10%).

2.     Electric only mode can be used during low speed driving where engines are inefficient and can give a further improvement of around 5mpg (17%).

3.     Regenerative braking, where braking force is provided by the electric motors, captures the kinetic energy of the car as electrical energy and will deliver a further 7mpg (21%).

Adding all of these together gives an overall improvement of about 15mpg (50%) on average both for fuel economy and CO2 emissions.  So our family car as a hybrid will have 60mpg (4.7 l/100km, 125 g/km CO2) as a diesel HEV and over 45mpg (6.2 l/100km, 150 g/km CO2) as a petrol HEV.  This benefit will depend on driving conditions so someone motorway driving will see a lesser benefit and in-town driving will be better.

Where we will all notice this most is in our pocket with reduced running costs.  At current UK fuel prices, the diesel car example would see costs reducing from 12p/mile to 9p/mile (25%) and the petrol car from 17p to 11p (35%).  Interestingly, the benefits for the petrol car are greater reducing the gap to diesel. Similar percentage benefits are seen over a wide range of cars with larger benefits for larger cars.  One final point is that a plug-in hybrid (PHEV) can reduce running costs even further.  On electrical power, this cost will be about 5p/mile: perhaps not as much as you might expect but significant.  So with a typical PHEV giving about 25 to 30 miles EV range, this can generate good monthly saving on fuel and large reductions of CO2 emissions on the road to Net Zero Emissions.

Bio – Professor Roy Douglas
Roy is Chief Technical Officer, a Director and one of the founders of Catagen Ltd.  He is also Professor of IC Engines Technology in the School of Mechanical and Aerospace Engineering at Queen’s University, Belfast.  He has over 40 years of experience in the areas of engine research and development, systems modelling and automotive after-treatment.  For the past 25 years, his research has concentrated on improving the performance of automotive after-treatment systems, with particular emphasis on applied catalysis at the interface between chemistry and engineering.  He is keenly interested in improved air quality through application of ultra-low emissions technology on the roadmap to zero tailpipe emissions for the automotive industry.

He has published over 100 technical papers with 4 granted patents: he has supervised over 40 PhD research students and over 20 Post-doctoral research fellows; he has research earnings of over £20 million and he is involved in current research projects valued at £7.5 million.

He is a senior member of the School of Mechanical & Aerospace Engineering and a member of the school management team.  He is currently a member of the Automotive Council Technical Committee in the UK and a member of the International Advisory Board for the Virtual Vehicle Research Centre at TU Graz, Austria.