Diesel Engine vs. EV: Which is better?

Are diesel engines better than EVs? Or the other way around? Let's have a quick look under the hood.

Diesel Engine vs. EV: Which is better?
diesel versus EV 1, 2

Diesel versus EV, fight! Which of these two vehicle propulsion types is better than the other?

SEE ALSO: THE DIFFERENCE BETWEEN GASOLINE AND DIESEL ENGINES

As you will soon find out, this is not as simple a question to answer as it might seem on the surface. Whilst you are likely to have an opinion on the matter, the truth is a little more nuanced than you might initially believe.

Are electric cars better than diesel?

In order to determine which is better, you really need to define the metrics you are referring to. In other words, better how?

If we are talking about fuel efficiency, noise pollution, and air quality, then EVs are clearly the outright winner. If, however, we are talking about torque or initial price, then Diesel engined cars will win.

But it must be born in mind that some components of EVs can be particularly bad for the environment during assembly and decommission. Especially their batteries

diesel versus EV batteries
Source: depositphotos

The answer really does depend on what is important to you. For many, fuel economy, range, initial price, and after-sales maintenance costs are likely the decisive factors when buying a new car.

Depending on the type of vehicle, and desired use, you may have your hand forced. For instance, if you need a vehicle that packs a lot of pulling power, you will need a diesel engine - hands down. 

Whilst there has been some headway made in developing EV trucks, for example, diesel engined versions are likely going to dominate the market for some time to come.

But, as EV technology develops it is not out of the question to see diesel usurped in the near future. Whilst companies, like Tesla, believe electric trucks will be cleaner and cheaper to operate than their diesel counterparts, it's not a done deal.

Those in favor of diesel engines will tell you, that for long-haul freight fleets, range and recharging will be a huge hurdle for massive 18-wheelers than domestic-sized cars.

A spokesman for the engine maker Cummins Inc., John Mills, told Bloomberg that, “Right now, we don’t think it’s viable,”

“more viable where you have shorter routes, less loads and you’re able to recharge.”

Advertisement

Whilst diesel and EV engines have their pros and cons, ultimately it will come down to personal choice and practical requirements from the vehicle in question by the buyer. Unless Government intervention forces their hand here too.

Is an electric car really more efficient?

This is a tricky one to answer easily. Whilst there are plenty of claims that EVs are no more efficient than internal combustion engines, you must bear in mind that these sources might be ever so slightly biased.

According to the US Department of Energy’s Office of Energy Efficiency and Renewable Energy, “EVs convert about 59%–62% of the electrical energy from the grid to power at the wheels. Conventional gasoline vehicles only convert about 17%–21% of the energy stored in gasoline to power at the wheels.”

Advertisement

But we are talking here about diesel engines, they can at least double this claim for gasoline engines.

Of the electricity delivered and stored in the EVs battery, it is estimated that between 85% and 90% of that is efficiently used by the car's electrical motor. In other words, that is the amount of energy used for useful work by the machine.

Vehicles

Diesel Cars Are Cleaner Than Some EVs, New Study Suggests

The difference between the overall efficiency claimed by the US Department of Energy’s Office of Energy Efficiency and Renewable Energy and an EVs motor efficiency can be accounted for by losses attributed to charging and discharging the battery and, for some charging (for some cars), converting AC to DC current and back again.

Advertisement

To hash out the point a bit more, here is an interesting discussion by Brian Feldman on Quora. But remember this discussion talks about gasoline engines, for reference diesel fuel has about 38 kWh per gallon (8.3 kWh/l)  and modern diesel engines tend to be around 70 mpg (29.7 km/l). roughly:-

“Consider the Tesla Model S, which has an available 85 kWh battery and a 265-mile range. 

Consider a similar gas-powered car, which gets 35 mpg. Gasoline contains about 33 kWh of energy per gallon. 

The Tesla uses 320 Wh/mile of energy (85 kWh/265 miles). The gas powered car uses 940 Wh/mile of energy (33 kWh/35 miles). 

Advertisement

Once the energy is on board (not counting the efficiency of the power generation, oil refining, or charging), the Tesla is using only about a third as much energy as the comparable gasoline-powered car.”

Based on our average figures supplied for diesel engines, EVs are still more efficient, by about a third, based on this basic calculation.

"But", you might ask, "that electricity is generated from fossil-fuel powered power plants". Whilst this is certainly true for a large proportion of grid-supplied electricity around the world, is this really fair?

After all, for diesel internal combustion engines, the oil needs to be found, extracted, refined and transported to fuel stations before it is ever pumped into the tank. This is, more or less, comparable to the supply of fossil fuels to power plants for electrical generation. 

Advertisement

But as each country's energy mix starts to integrate more and more renewable and low-emission sources (nuclear, wind, solar etc), the gap between diesel and EV will only continue to expand on this front.

But in the spirit of fairness, this doesn't begin to consider the impact of biodiesels with regards to future sustainability and environmental impact.

The Pros and Cons of EV and Diesel Engines

For ease of reference, and with thanks to allstarcard.co.uk, we have created the following table to explore the pros and cons of both types of engine. This is not intended, in any way, to be comprehensive and is just for illustrative purposes.

Advertisement
Pros
Electrical Vehicles Diesel Engines
Zero emissions (excluding grid-supplied generation) Lower lifetime cost than petrol because of lower depreciation
Minimal noise pollution and a quiet traveling experience Engines last longer and tolerate much higher mileages than petrol
Zero road tax and congestion charging More efficient (by around 25% compared to petrol) so fuel costs are less, providing pump prices stay close. Diesel’s better mpg becomes more pronounced over long distance journeys. Some diesel engines can even be more fuel-efficient than a petrol hybrid
Presents a green image - but not a tangible benefit Produce less CO2, so road tax is lower than petrol - but depends on the policy
High residual value Higher torque or pulling power means a mid-range acceleration of larger diesel cars is often better than sports cars. This pulling power is why diesel is used for commercial vehicles: it can pull much greater loads than any other option here
Instant acceleration Tend to depreciate at a lower rate than petrol/gasoline engines
Initial costs can be reduced from Government incentives and tax breaks Diesel engines can deal with various fuel types beyond conventional diesel. Biodiesels could be a game changer for diesel engines in the future
Maintenance costs are much lower over the vehicles lifetime compared to internal combustion engines  
Cons
Electrical Vehicles Diesel Engines
Expensive to buy More expensive than petrol to buy (historically)
Limited range Produce nitrous oxides, hydrocarbons, and particulates, so not necessarily greener than petrol and definitely at a disadvantage compared to EVs
Extensive time to recharge Insurance is higher for diesel engines rather than petrol engines, by up to 15% - because they cost more to replace or repair
Scarcity of recharging points Engines generally require a little less routine servicing but if they do go wrong, repair costs are higher. Latest figures show diesel engines are slightly less reliable than petrol
Electricity is usually generated by fossil fuel power stations so in essence defeats the purpose of ‘going green’ Volatile fuel price
Danger to pedestrians of silent approach Oil is a finite resource

Please note that the above is a rough summary of each type of engines' pros and cons - it isn't comprehensive by any means. At the end of the day, your particular needs and wants will ultimately drive (excuse the pun), your choice of engine. 

But, as time goes by, the pressure is likely to mount on diesel engines from environmentalists the world over. If oil does become scarcer and prices rise, basic economics might well be "straw that broke the camels back" for any battle between EVs and diesel engines.

Unless biodiesel can "save its bacon" in the future. Only time will tell.