Carlos Ghosn, the CEO of Nissan and Renault, has proclaimed that
battery-powered vehicles will account for 10 percent of global new-car
sales by 2020. Mr. Ghosn, of course, is planning to introduce at least
four electric cars in the next three years. Independent analysts,
however, such as Tim Urquhart of IHS Global Insight, believe that
battery-powered vehicles will remain at less than one percent of the
new-car mix in 2020.
Carlos Ghosn, the CEO of Nissan and Renault, has proclaimed that
battery-powered vehicles will account for 10 percent of global new-car
sales by 2020. Mr. Ghosn, of course, is planning to introduce at least
four electric cars in the next three years. Independent analysts,
however, such as Tim Urquhart of IHS Global Insight, believe that
battery-powered vehicles will remain at less than one percent of the
new-car mix in 2020.
But they won’t be the same IC engines that power vehicles today. With
federal fuel-economy standards getting tougher by 35 percent over the
next five years, IC efficiency must improve dramatically—if not, we’ll
all be forced to drive econoboxes.
After speaking with key powertrain engineers and some independent
inventors, we’ve examined some of the technologies that can achieve this
improved efficiency.
Spraying fuel directly into a gasoline engine’s combustion chambers
instead of its intake ports isn’t a new idea—the World War II ME109
German fighter plane used it. The Japanese-market Mitsubishi Galant was
the first car to combine direct injection with computer-controlled
injectors in 1996. Direct injection (DI) costs more than port injection
because the fuel is sprayed at 1500–3000 psi rather than 50–100 psi, and
the injectors must withstand the pressure and heat of combustion.
But DI has a key benefit: By injecting fuel directly into the cylinder
during the compression stroke, the cooling effect of the vaporizing fuel
doesn’t dissipate before the spark plug fires. As a result, the engine
is more resistant to detonation—a premature and near-explosive burning
of the fuel, producing a knocking sound and pounding the pistons with
pressure and heat—and can therefore operate with a higher compression
ratio—about 12:1 instead of 10.5:1. That alone improves fuel economy by
two to three percent.
And DI also offers the possibility of lean combustion because the fuel
spray can be oriented so that there is always a combustible mixture near
the spark plug. That could yield five percent more efficiency.
Several European carmakers are already using this lean-burn strategy.
Unfortunately, lean combustion causes higher tailpipe emissions of NOx
(oxides of nitrogen), which run afoul of America’s tighter limits.
Catalysts that can solve this problem don’t like the high sulfur content
in American gasoline. New catalysts promise to reduce emissions.
Meanwhile, expect direct injection to become universal by 2020.
Direct -Injection
TURBO
Modern engines achieve power levels that we could only dream about 20
years ago. The downside is that during routine driving, most engines are
loafing—and 300-hp engines are inefficient when they’re only putting
out the 30 ponies needed to push an average sedan down the highway. When
an engine’s throttle is barely cracked open, there’s a strong vacuum in
the intake manifold. During the intake stroke, as the pistons suck
against this vacuum, efficiency suffers.
The classic solution to this problem is to make an engine smaller. A
small engine works harder, running with less vacuum, and is consequently
more efficient. But small engines make less power than big ones.
To make big-engine power with small-engine fuel economy, many companies
are turning to smaller engines with turbochargers, direct fuel
injection, and variable valve timing. These three technologies work
together to their combined benefit.
Forcing additional air into an engine’s combustion chambers with a
turbocharger definitely boosts power; car manufacturers have been doing
this for years. But in the past, in order to avoid harmful detonation,
turbocharged engines needed lower compression ratios, which compromised
efficiency.
As we’ve seen, direct fuel injection helps solve this problem by cooling
the intake charge to minimize detonation. Second, if the variable valve
timing extends the time when both the intake and the exhaust valves are
open, the turbocharger can blow fresh air through the cylinder to
completely remove the hot leftover gases from the previous combustion
cycle. And since the injectors squirt fuel only after the valves close,
none of it escapes through the exhaust valve.
The first engine in America with all three of these elements was the
base 2.0-liter four-cylinder in the 2006 Audi A4. It had a 10.5:1
compression ratio—as high as many naturally aspirated engines—despite a
peak boost pressure of 11.6 psi. It produced 200 horsepower and 207
pound-feet of torque.
Ford’s EcoBoost system is nothing more than direct injection and
turbocharging. Dan Kapp, Ford’s director of advanced powertrain
engineering, says that this technology will spread across the company’s
cars and trucks. “Nothing else delivers double-digit improvements in
fuel efficiency at a reasonable cost.”
In the future, Ford expects to replace its 5.4-liter V-8 with a
3.5-liter EcoBoost V-6; its 3.5-liter V-6 with a 2.2-liter EcoBoost
inline-four; and its 2.5-liter inline-four with a 1.6-liter EcoBoost
inline-four. In each downsizing, peak power should be similar, low-end
torque should be about 30 percent greater, and fuel economy should be
10-to-20 percent higher. The only downside will be an added charge of
$1000 or so to the price of DI-turbo vehicles to pay for the additional
hardware.
BMW, Mercedes, Toyota, and Volkswagen are planning similar engines—some
using superchargers instead of turbochargers. Turbocharging with direct
injection will continue to expand.
Later in the decade, we will see a second generation of these engines,
using higher boost pressures. This will allow further engine downsizing
to achieve an additional 10-percent efficiency improvement.
Making this happen will require cooled exhaust-gas recirculation to
control detonation and either staged or variable-geometry turbos to
limit customary lag. Those technologies are already in use on diesel
engines, but a gas engine’s higher exhaust temperatures pose durability
problems that must be solved before carmakers can deploy these
technologies.
Variable- Displacement
Another way to improve the efficiency of a big engine is to turn off
some of its cylinders. Since the throttle must be opened farther to get
the same power from the remaining cylinders, intake-manifold vacuum goes
down and efficiency goes up.
In real-world driving, this can produce a fuel-economy improvement of
five percent, at a fairly low cost. The technology is particularly cost
effective on pushrod, two-valve engines, which is why we’ve seen
variable displacement on GM and Chrysler V-8s.
Honda uses variable displacement on its 24-valve V-6 engines, but the
additional hardware to close the multiplicity of valves adds cost.
Moreover, shutting off some cylinders on a V-6 generates more vibration
and noise problems than it does with a V-8 because V-6s have coarser
firing impulses and poorer inherent balance. The active engine mounts
and variable intake manifolds needed to solve these problems add further
costs.
Variable valve timing & Lift
The simplest implementation of variable valve timing started about 25
years ago, using a two-position advance or retard of either an engine’s
intake or exhaust camshaft to better match the engine’s operating
conditions. Today, most four-valve-per-cylinder DOHC engines have
continuously variable phasing on both the intake and the exhaust
camshafts.
About 20 years ago, Honda introduced a more elaborate approach with its
VTEC system, which shifted between two (and later, three) separate sets
of cam lobes—one for high-speed operation and one for low. VTEC can also
simply turn off one of a cylinder’s two intake valves under light
loads. In 2001, BMW went a step further with its Valvetronic system,
which can continuously vary the opening stroke of the intake valves to
optimize engine power and efficiency. Furthermore, this extensive
control of the intake valves serves to replace a throttle plate, which
eliminates vacuum and therefore reduces pumping losses.
Though they provide efficiency benefits, variable-lift systems are
complex and expensive. Development continues on purely electronic
systems that could replace camshafts and simply open and close an
engine’s valves according to a computer. But electronic valve-opening
mechanisms are also costly and consume significant power. GM Powertrain
VP Dan Hancock suggests that a two-stage valve-lift mechanism can
deliver 90 percent of the benefits of fully variable lift. Moreover,
Ford’s Kapp says that the benefits of variable valve lift are limited
when combined with EcoBoost (DI turbo).
On the other hand, BMW, with its latest single-turbo, direct-injection
3.0-liter inline-six (N55) that’s replacing the twin-turbo (N54) across
the lineup, has done just that by adding Valvetronic to its DI-turbo
configuration. Combined with the move from a six-speed automatic to an
eight-speed, the change is said to provide 10 percent more miles per
gallon.
