Question

Explain the pros and cons of an HCCI engine. Why isn’t it a viable engine technology at the moment?

Answer 1

pros of HCCI engine are:

1)Since HCCI engines are fuel-lean, they can operate at diesel-like compression ratios (>15), thus achieving 30% higher efficiencies than conventional SI gasoline engines.

2)Homogeneous mixing of fuel and air leads to cleaner combustion and lower emissions. Because peak temperatures are significantly lower than in typical SI engines, NOx levels are almost negligible. Additionally, the technique does not produce soot.

3)HCCI engines can operate on gasoline, diesel fuel, and most alternative fuels.

4)HCCI avoids throttle losses, which further improves efficiency.

Cons of HCCI engine are:

1)

Achieving cold start capability.

High heat release and pressure rise rates contribute to engine wear.

Autoignition is difficult to control, unlike the ignition event in SI and diesel engines, which are controlled by spark plugs and in-cylinder fuel injectors, respectively.

2)HCCI engines have a small power range, constrained at low loads by lean flammability limits and high loads by in-cylinder pressure restrictions.

3) carbon monoxide and hydrocarbon emissions are higher than spark ignition during incomplete combustion.

It isn't viable engine technology at the moment, as the control system is more challenging than using a spark plug or fuel injector to determine ignition timing as in SI and CI engine respectively.