Internal Combustion Engines Hybrid Powertrains and Fuel Cells

The following section primarily discusses passenger car engines and fuels. The internal combustion engine is more than 100 years old, yet full of life. Further development regarding increased efficiency (or reduced fuel consumption) has by no means been reached. The internal combustion engine will be the primary power plant for decades to come in spite of what might be said otherwise. Admittedly, the internal combustion engine, in particular the gasoline engine, is fairly bad at low loads typical for passenger car applications. The gasoline engine can be improved by applying variable valve timing, cylinder deactivation, downsizing and supercharging, startstop automatic, gasoline direct injection and reduced friction. All told, the potential might end up in excess of over 30%. Some of these elements are already used today, however, on a too-limited basis. For instance, it is hard to understand why downsizing and supercharging are not used much more — the benefits in fuel consumption are some 10%. Or why do we not use start-stop automatic devices much more? The benefits can also reach 10%. The diesel engine, being better in fuel economy when compared to the gasoline engine, can also be made more efficient by improving supercharging, start-stop automatic, combustion characteristics and reduced friction. The potential might reach some 20% or more.

The picture is not complete without talking about exhaust gas emissions. Today, the passenger car engine, provided it incorporates the latest technologies, is no longer polluting the environment — it is in fact an air cleaning device (SULEV-standard, gasoline). These excellent results were achieved because of exhaust gas emission regulations implemented in California. Compared to 1970 (when legislation got started), nitric oxides were reduced by 99%, hydrocarbons by 99.8% and carbon monoxide by 93% (SULEV-standard). It is interesting to note that these improvements were not achieved because of an initiative of the automotive industry — this industry said it would not be necessary and that it would be very expensive to reduce emissions!

The next step to reduce CO2-emissions is to switch to natural gas. Natural gas is definitely a transition fuel on the long way to a sustainable energy future. ETH Zurich, together with the Swiss Federal Laboratories for Materials Testing and Research (EMPA) and others developed a novel passenger car gas engine with supercharging, high compression ratio, exhaust gas recirculation and a new gear box leading to a reduction of 33% in CO2 emission when compared to a sister engine of the same power fuelled with gasoline.

Next, with more complexity comes the hybrid powertrain. As mentioned earlier, internal combustion engines, particularly the gasoline engine, do show average driving cycle efficiencies of below 20%. With a hybrid powerplant, low loads are covered by an electric motor with efficiencies far higher than those of the internal combustion engine. This motor can be reversed to operate as a generator to recover brake energy and thus further enhance cycle efficiency. All told, hybrid powerplants, depending on driving the cycle considered, can improve the fuel consumption by 20% or more. Figure 5 shows a schematic of a hybrid powertrain.

- CI or SI engine

- engine with start/stop automatic

- electric motor for deep part load

- no ZEV-operation

- recuperation

- different types of batteries

- supercap

- no battery charging from grid

- 5-speed transmission for engine

- 1-speed for electric motor

Fig. 5. Scheme of hybrid powertrain parallel hybrid engine

0000

electric motor h=K)

transmission wheel

Fig. 6. Scheme of ETH Zurich Hybrid III

Table 1. Results of ETH Zurich Hybrid III

Guide to Alternative Fuels

Guide to Alternative Fuels

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