After posting about the Honda clean diesel ad (earlier post), I decided to do some quick side-by-side comparisons using three models of the Honda Accord: the Accord Diesel featuring the new, clean 2.2 i-CTDi engine touted in the ad (picture at right), the new Accord Hybrid, and two gasoline sedans. The outcome: the Accord Diesel (using petroleum diesel) offers the lowest fuel consumption and the lowest CO2 emissions, even surpassing the Accord Hybrid.
In a sense, it’s not a fair comparison—the cars, even though they are of the same model family, target different consumers with different levels of performance and features. (Furthermore, the diesel isn’t offered in the US.) Honda opted to create a performance hybrid with its Accord, thereby somewhat reducing the fuel consumption and CO2 emissions benefits. Had the company implemented its IMA hybrid drive with a smaller, more efficient gasoline engine, the results would be much better.
Nevertheless, the comparison across different powertrains in the same model is interesting. The table below compares the Accord Hybrid, the Accord Diesel 2.2 i-CTDi Sport, the EX Sedan and the LX V-6.
|2005 Accord Hybrid Sedan||2005 Accord i-CTDi Sport||2005 Accord EX||2005 Accord LX-V6|
|1. Grams CO2/km for all vehicles except the diesel estimated by using a factor of 19.36 pounds CO2 per gallon of gasoline (2.32 kg/liter). Actual result will vary with driving pattern, fuel composition, and so on.|
|Power Output (hp)||16|
|Acceleration 0-60 (seconds)||7.5||9.3||9.4||8.0|
|Combined mpg (US)
Comparing the i-CTDi and the EX highlights some of the efficiency and benefits of the diesel platform. Although the gasoline engine is slightly larger, the diesel offers incrementally better acceleration (due to the greater low-rpm torque), 33% better fuel consumption and approximately 25% less CO2.
The amount of CO2 emitted by a car is dependent on the composition of the fuel burned, the completeness of the combustion, and the total amount of fuel consumed. Gallon for gallon, diesel fuel will produce more CO2 than gasoline—but because diesels tend to be more fuel efficient, a diesel delivering equivalent performance to a gasoline engine will produce less carbon dioxide than its gasoline counterpart—exactly what we see in the table above. A diesel engine burning a biodiesel blend will improve upon that even more dramatically.
By maintaining a larger engine in the Accord Hybrid to optimize power and performance for the driving experience, Honda traded off some potential gains in fuel economy and CO2 emissions.
Honda offers a terrific animated introduction to the technology of the diesel i-CTDi here. It’s well worth the look if you are interested in how Honda designed and engineered this engine.